QP34- 


Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 

Open  Knowledge  Commons  (for  the  Medical  Heritage  Library  project) 


http://www.archive.org/details/kirkeshandbookof1889kirk 


BL0QD-5PECTRA  COMPARED  WITH  SPECTRUM  DFARGANQ-LAf 


1  Spectrum  oP  Ardand-lamp  with  Fraunhoters  lines  in  position. 

2  Spectrum  oF  Oxyhaemoqlobin  in  diluted  blood. 

3  5pectrum  dP  Reduced  rTsemDCilobin. 

4  Spectrum  oF  Carbonic  oxide  Haemoglobin. 

5  Spectrum  oP  Acid  liaematin  in  etherial  solution. 

6  Spectrum  oP  Alkaline  Plsmatin. 

/  Spectrum  dF  ChloroForm  Extract  nF  acidulated  Dx-Bile. 

8  5pectrumaF  MethafmoOjQbin. 

f)  Spectrum  dF  Haemochromaden. 

10  Spectrum  oF  PlaematoporpKyrin. 

\tad  aj'tiie  above  Spectra  hare  been  /{rami  fivm  observations  by  MTKIepraik  ECS 


KIEKES'  HANDBOOK  OF   PHYSIOLOGY 


HAND-BOOK 


OF 


PHYSIOLOGY 


W.  MORRANT  BAKER,  F.R.C.S. 

surgeon  to  st.  Bartholomew's  hospital  ;  member  of  the  court  op  examiners  of  the  royal 

college  of  surgeons  ;  examiner  in  surgery  in  the  university  of  london  and 

at  the  royal  college  of  physicians  j  late  lecturer  on  physiology 

at  st.  bartholomew's  hospital, 


VINCENT  DORMER  HARRIS,  M.D.  Lond. 

FELLOW  OF  THE  ROYAL    COLLEGE    OF    PHYSICIANS  ;      EXAMINER    IN    ELEMENTARY    PHYSIOLOGY   AT  THE 

CONJOINT    BOARD    OF    THE    ROYAL    COLLEGES    OF    PHYSICIANS  AND   SURGEONS  ;    DEMONSTRATOR 

OF  PHYSIOLOGY  AT  ST.  BARTHOLOMEW'S   HOSPITAL  ;   PHYSICIAN  TO  THE  VICTORIA 

PARK   HOSPITAL   FOR   DISEASES   OF  THE   CHEST 


TWELFTH     EDITION 


REARRANGED,     REVISED     AND    REWRITTEN,    AND    WITH 
FIVE   HUNDRED    ILLUSTRATIONS 


NEW  YORK 
WILLIAM     WOOD     &     COMPANY 

56  &  58  Lafayette  Place 
1  8  8  9 


press  or 

8TETTIHER,    LAMBERT     4    CO., 

22,   24  &  26  READE  ST., 

NEW  YORK. 


(8 


PREFACE  TO  THE  TWELFTH  EDITION. 


It  has  been  found  necessary  to  make  a  considerable  number  of 
alterations  in  the  Twelfth  Edition  of  Kirkes'  Physiology.  Many  of 
these  have  been  in  the  earlier  chapters,  and  in  the  sections  on  The 
Blood,  The  Heart,  and  The  Muscular  System ;  while  the  chapters  on 
The  Nervous  System,  on  The  Keproductive  Organs,  and  on  Develop- 
ment have  been  re-arranged  and  to  a  great  extent  re-written.  About 
fifty  new  illustrations  have  been  added.  In  those  chapters  which  treat 
of  the  subjects  of  which  the  junior  student  is  expected  to  exhibit  a 
knowledge  at  his  first  examination,  some  details  which  may  be  omitted 
on  first  reading  have  been  printed  in  smaller  type;  they  must  not, 
however,  be  considered  for  this  reason  to  be  unimportant. 

Without  attempting  to  enumerate  all  the  important  text-books  on 
Physiology  and  monographs  on  physiological  subjects  of  which  use  has 
been  made  in  preparing  the  present  edition,  and  to  the  authors  of 
winch  we  beg  to  record  our  obligations,  we  would  mention  especially 
those  of  Drs.  Gaskell,  Gowers,  Halliburton,  and  Wooldridge ;  Landois 
and  Stirling's  Text-book,  and  the  works  of  the  late  Prof.  F.  M.  Bal- 
four. Dr.  Gowers  has  kindly  allowed  us  to  copy  several  of  the 
diagrams  from  his  works  on  the  Nervous  System. 

Our  thanks  are  due  to  Dr.  T.  W.  Shore,  who  has  kindly  helped  us 
in  revising  and  seeing  through  the  press  certain  sections,  particularly 
those  relating  to  biological  questions. 

Mr.  Daniellson  has  undertaken,  as  in  the  two  previous  editions,  the 
drawings  upon  wood  and  the  engraving  of  all  the  new  illustrations,  and 
has  carried  out  the  work  with  much  skill. 

W.  MORRANT  BAKER. 
VINCENT  D.  HARRIS. 


IV  PREFACE    TO    T^E    TWELFTH    EDITION.1 

In  the  preparation  of  the  present  edition  it  seems  only  right  to 
state,  that  while  I  am  responsible  with  my  colleague,  Dr.  Yincent  D. 
Harris,  for  the  general  supervision  of  the  work  in  its  passage  through 
the  press,  he  has  undertaken  the  labor  of  investigation  and  the  arrange- 
ment of  the  details.     Many  parts,  moreover,  he  has  re-written. 

And  to  him  has  fallen  in  chief  part  the  difficult  task  of  selecting 
from  the  many  new  facts  and  observations  which  have  been  published 
within  the  last  few  years  such  as  can  fitly  find  "a  place  in  a  handbook 
for  students. 

W.  MORRANT  BAKER. 

September,  1888. 


CONTENTS. 


CHAPTER   I. 


The  Phenomena  of  Life, 


PAGE 

1 


CHAPTER   II. 

The  Structure  of  the  Elementary  Tissues, 
Cells, 

Nucleus, 

Intercellular  Substance, 

Fibres, 

Tubules,   . 

Epithelium,  . 

Connective  Tissues, 

The  Fibrous  Tissues, 

Cartilage, 

Bone, 


15 
15 
16 

17 
18 
18 
19 
29 
32 
40 
44 


CHAPTER  III. 

The  Blood,    ....... 

Quantity  of  Blood,    . 

Coagulation  of  the  Blood,  . 

Conditions  affecting  Coagulation,    . 

The  Blood-Corpuscles,     . 

Physical  and  Chemical  Characters  of  Red  Blood-Cells, 

The  White  Corpuscles,  or  Blood-Leucocytes,    . 

Chemical  Composition  of  the  Blood, 

The  Serum,  ...... 

Gases  contained  in  the  Blood, 

Blood-Crystals,     ...... 

Derivatives  of  lhemoglobin, 

Development  of  the  Blood,         . 

Uses  of  the  Blood,     ..... 

CHAPTER   IV. 

Circulation  of  the  Blood,  . 

The  Systemic,  Pulmonary,  and  Portal    Circulations, 


57 
r.7 
58 
66 
70 
70 
74 

;: 

78 
81 
84 
86 
91 
94 


95 

96 


VI 


CONTENTS. 


The  Heart,  ...... 

Structure  of  the  Heart  and  its  Valves, 

Structure  of  the  Arteries,  Capillaries,  and  Veins, 
Physiology  of  the  Heart, 
Physiology  of  the  Arteries, 
Physiology  of  the  Capillaries, 
Physiolog3r  of  the  Veins, 

Velocity  of  the  Circulation, 

Velocity  of  the  Blood  in  the  Arteries,    . 

"        "      Capillaries, 

"         "      Veins, 
Velocity  of  the  Circulation  as  a  whole, 


Peculiarities  of  the  Circulation  in  Different 
Circulation  in  the  Brain, 
Circulation  in  the  Erectile  Structures,    . 
Agents  concerned  in  the  Circulation, 
Discovery  of  the  Circulation, 
Proofs  of  the  Circulation  of  the  Blood, 


Parts, 


97 
97 

105 
115 
134 
153 
156 

158 
159 
160 
160 
161 

162 
162 
163 
165 
165 
165 


CHAPTEE   V. 

Respiration,  .... 

Position  and  Structure  of  the  Lungs, 
Structure  of  the  Trachea  and  Bronchial  Tubes 
Structure  of  the  Lungs  and  Pleura, 
Mechanism  of  Respiration, 
Respiratory  Movements, 
Quantity  of  Air  respired, 
Vital  or  Respiratory  Capacity, 
Force  exerted  in  Respiration, 
Changes  of  the  Air  in  Respiration,  . 
Changes  produced  in  the  Blood  by  Respiration, 
Mechanism  of  various  Respiratory  Actions, 
Influence  of  the  Nervous  System  in  Respiration 
Effects  of  Vitiated  Air — Ventilation, 
Effect  of  Respiration  on  the  Circulation, 
Apnoea — Dyspnoea — Asphyxia, 


167 
168 
170 
174 
178 
179 
184 
184 
186 
187 
193 
193 
197 
199 
200 
204 


CHAPTER  VI. 

Food  and  Diet,        ..... 

Classification  of  Foods, 

Foods  containing  chiefly  Nitrogenous  Bodies, 
"  "       Carbohydrate  Bodies, 

"  "  "      Fatty  Bodies, 

Substances  supplying  the  Salts,    . 

Liquid  Food,    ..... 


208 
209 
210 
212 
213 
213 
213 


CONTENTS. 


Vll 


Pood  and  Diet — continued. 
Effects  of  Cooking, 
Effects  of  an  Insufficient  Diet, 

Starvation, 
Effects  of  Improper  Food, 
Effects  of  too  much  Food, 
Diet  Scale, 


CHAPTER    VII. 


Digestion, 


Passage  of  Food  through  the  Alimentary  Canal, 

Mastication,  ....... 

The  Teeth,     ....... 

Insalivation,         ....... 

The  Salivary  Glands  and  the  Saliva, 

Structure  of  the  Salivary  Glands,  .... 

The  Saliva,     ....... 

Influence  of  the  Nervous  System  on  the  Secretion  of  Saliva, 
The  Pharynx,  ...... 

The  Tonsils,         ....... 

The  Oesophagus  or  Gullet,    ..... 

Swallowing  or  Deglutition,        ..... 

Digestion  of  Food  in  the  Stomach, 

Structure  of  the  Stomach,  ..... 

Gastric  Glands,  ...... 

The  Gastric  Juice,  ...... 

Functions  of  the  Gastric  Juice,        .... 

Movements  of  the  Stomach,        . 

Influence  of  the  Nervous  System  on  Gastric  Digestion,     . 

Digestion  of  the  Stomach  after  Death, 

Vomiting,       ....... 

Digestion  in  the  Intestines,      ..... 
Structure  of  the  Small  Intestine,      .... 
Structure  of  the.  Large  Intestine,  .... 

The  Pancreas  and  its  Secretion,       .... 
Structure  and  Functions  of  the  Liver,  .... 

The  Bile, 

The  Liver  as  a  Blood-elaborating  Organ, 

Succus  Entericus,      ...... 

Summary  of  the  Changes  which  take  place  in  the  Food  during 
through  the  Small  Intestine,        .... 

Summary  of  the  Process  of  Digestion  in  the  Large  Intestine, 
Movements  of  the  Intestines,  .... 

Influence  of  the  Nervous  System  on  Intestinal  Digestion, 
Defalcation,  ....... 

■Gases  contained  in  the  Stomach  and  Intestines, 


its 


Till 


CONTENTS. 


CHAPTEE   VIII. 

Absorption,  ...... 

The  Lacteal  and  Lymphatic  Vessels  and  Glands, 
Properties  of  Lymph  and  Chyle, 
Absorption  by  the  Lacteal  Vessels, 
Absorption  by  the  Lymphatic  Vessels, 
Absorption  by  Blood-vessels, 

CHAPTER    IX. 

Animal  Heat,  ..... 

Variations  in  Bodily  Temperature, 
Sources  of  Heat,  .... 

Loss  of  Heat,  .... 

Production  of  Heat,        .... 
Inhibitory  Heat-centre, 


PAGE 

298 
298 
308 
309 
310 
311 


316 
316 
318 
320 
322 
323 


CHAPTER   X. 


Secretion, 


325 


CHAPTER  XL 

The  Structure  and  Functions  op  the  Skin, 


340 


CHAPTER    XII. 

The  Structure  and  Functions  op  the  Kidneys, 
Structure  of  the  Kidneys, 
Structure  of  the  Ureter  and  Urinary  Bladder, 
The  Urine,     ...... 

Micturition,  ..... 


353 
353 
359 
361 

382 


CHAPTER  XIII. 


The  Vascular  Glands, 


383 


CHAPTER  XIV. 


The  Muscular  System,      ..... 

.     394 

Causes  and  Phenomena  of  Motion, 

394 

Plain  or  Unstriped  Muscle,         .... 

.     394 

Striated  Muscle,        ..... 

396 

Chemical  composition  of  Muscle, 

.    401 

Physiology  of  Muscle  at  rest, 

403- 

in  activity, 

.     406 

Rigor  Mortis,              ..... 

419 

Actions  of  the  Voluntary  Muscles, 

..    421 

"      Involuntary  Muscles, 

426 

Electrical  Currents  in  Nerves,    .... 

.     427 

CONTENTS. 


CHAPTER  XV. 

Nutrition  :  The  Income  and  Expenditure  of  the  Human  Body, 
Nitrogenous  Equilibrium  and  Formation  of  Fat, 


PAGE 

432 
435 


The  Voice  and  Speech, 


CHAPTER   XVI. 


437 


CHAPTER  XVII. 

The  Nervous  System,       .... 
Elementary  Structures  of  the  Nervous  System, 
Functions  of  Nerve  Fibres, 
Laws  of  Conduction  in  Nerve  Fibres, 
Functions  of  Nerve  Centres, 


450 
450 
456 
458 
465 


CHAPTER  XVIII. 

Cerebro-spinal  Nervous  System,     ..... 

The  Spinal  Cord  and  its  Nerves,  .... 

Functions  of  the  Spinal  Cord,  ..... 

The  Medulla  Oblongata,  ..... 

Structure  and  Distribution  of  the  Fibres  of  the  Medulla  Oblangata, 
Functions  of  the  Medulla  Oblongata,    .... 

Pons  Varolii,  ....... 

Crura  Cerebri,      ....... 

Corpora  Quadrigemina,         ...... 

The  Cerebrum,        ....... 

Structure  of  the  Cerebrum,  ..... 

Functions  of  the  Cerebrum,        ..... 

The  Cerebellum,        ....... 

Structure  and  Functions  of  the  Cerebellum, 


472 
472 
481 
491 
491 
495 
499 
499 
500 

502 
503 
511 
524 
524 


CHAPTER  XIX. 

Physiology  of  the  Cranial  Nerves, 


530 


CHAPTER    XX. 


The  Senses, 

The  Sense  of  Touch, 
The  Sense  of  Taste, 
The  Sense  of  Smell, 
The  Sense  of  Hearing. 
The  Sense  of  Sight, 


546 
550 
556 
568 
56*3 


CHAPTER  XXI. 

The  Sympathetic  Nervous  System, 


626 


TZ  CONTENTS. 

CHAPTEK  XXIT. 

PAGE 

The  Reproductive  Organs,  .......  634 

CHAPTER    XXIII. 

Development,  .........     656 

The  Changes  in  the  Ovum,  .......  656 

Development  of  Organs,  .......     678 

CHAPTEK  XXIV. 
On  the  Relation  of  Life  to  other  Forces,       ....  713 

APPENDIX. 

The  Chemical  Basis  of  the  Human  Body,        ....  732 

APPENDIX  B : 

Anatomical  Weights  and  Measures,  .....      754 

Measures  of  "Weight,  .  .  . '  .  .  .  .  754 

"        "  Length,     .  .  .  .  . "  .  754 

Sizes  of  various  Histological  Elements  and  Tissues,        .  .  .  755 

Metrical  System  of  "Weights  and  Measures  compared  with  the  Common 

Measures,        ........  756 

Classification  of  the'  Animal  Kingdom,  .  .  .  .  756 


INDEX, 759 


XI 


*  Table  for  converting  Degrees 
of  the  FAHRENHEIT  Ther- 
mometer Scale   into   Degrees 
CENTIGRADE. 

MEASUREMENTS. 

FRENCH    INTO    ENGLISH. 

LENGTH. 

1  metre                           "] 

10  decimetres                    1 

100  centimetres                    f 

1,000  millimetres                  J 

=  39.37  English 

inches 
(or  1  yard  and 

H  in.) 

Fahrenheit.                             Centigrade. 
500°                                     260° 
401                                     205 
392                                    200 
383                                     195 
374                   ,                190 

356             180 

347                                   175 
338                                   170 
329                                   165 
•     320                                   160 
311                                   155 
302                                   150 
284                                   140 
275                 ,                  135 
266               ,                    130 
248                                   120 
239                 .                  115 

230             110 

212                                   100 
203                                     95 
194               ,  .                    90 
176                 .  ,                  80 
167                                     75 
140                                     60 
122                                     50 
113                                     45 
105                                     40.54 
104              ,  ,                      40 

100             37.8 

98.5                                  36.9 

95                                     35 

86                                   30 

77                                     25 

68                                     20 

50                                     10 

41                                       5 

32               Zero                0 

23                                 —  5 

14                               —10 

+  5                                 —15 

—  4                                 —20 

—13                                 —25 

—22                                 —30 

—40                                 —40 

—76                —60 

1  decimetre                     ) 

10  centimetres                   > 

100  millimetres                   ) 

=  3.937  inches 

(or      nearly       4 
inches) 

1  centimetre                    "j 
10  millimetres                   > 

1  millimetre 

=  .3937  or  about 
(nearly  §-inch.) 

= nearly  fa  inch. 

CAPACITY. 

1,000  cubic  decimetres   { 
1,000,000  cubic  centimetres  ) 

=1  cubic  metre 

1  cubic  decimetre          ) 

or                      V 

1,000  cubic  centimetres       ) 

=  1  litre 
(35i  fluid  oz., 
or   rather  less 
than  an  English 
quart) 

WEIGHT. 

1  gramme 
10  decigrammes                1 
100  centigrammes 
1,000  milligrammes               J 

=  15.432349  grs. 
(or  nearly  15£) 

1  decigramme                  ) 

10  centigrammes               > 

100  milligrammes                ) 

=  rather  more 
than  1^  grain 

1  centigramme                 ) 
10  decigrammes                 j 

=  rather  more 
than  -330-  grain 

1    degree  Fahr.  =  .54°  C 
1.8      "        "      =     1°  C 
3.6      "        "      =     2°  C. 
4.5      "        "       =     2.5°  C. 
5.4      "        "       =     3°  C. 

1  milligramme 

=  rather  more 
than  gg^y  grain 

*  Modified  from  Fownes'  Chemistry. 

Measure  of  i  decimetre,  or  io  centimetres,  or  ioo  millimetres. 

Illlllll       I       I       I       I      I       I       I       I       I      I       I      I       I       I       I       I 


10 


Highest 
point  of 
Crest  of  the 
Dium. 


Anterior  Su- 

.,  perior  Spine 

of  the  Ilium. 


Symphysis  PuLm, 


DIAGRAM    OF    THORACIC    AND    ABDOMINAL    REGIONS. 


A.  Aortic  Valve. 
M.  Mitral  Valve. 


P.  Pulmonary  Valve. 
T.  Tricuspid  valve. 


Cranium 


-  7  Cervical  Vertebrae 


12  Dorsal  Vertebrae. 
Humerus. 

5  Lumbar  Vertebras. 


Bones  of  tbe  Carpus. 
Bones  of    the    Meta- 
carpus. 
Phalanges  of  Fingers. 


Bones  of  the  Tarsus. 
Bones   of    the    Meta- 

tursus 
Phalanges  of  Toes. 


THE    SKELETON  (after  Holdkn). 


HANDBOOK  OF   PHYSIOLOGY. 


CHAPTER   I. 


THE   PHENOMENA   OF   LIFE. 

Human  physiology  is  that  part  of  animal  physiology  which  treats 
of  man — of  the  way  in  which  he  lives  and  moves  and  has  his  being. 
It  teaches  how  man  is  begotten  and  born;  how  he  attains  maturity, 
and  how  he  dies. 

As,  however,  man  is  a  member  of  the  animal  kingdom,  although 
separated  and  specialized  no  doubt  to  a  remarkable  degree,  he  during 
life  manifests  certain  characteristics — possesses  certain  properties  and 
performs  certain  functions — in  common  with  all  living  animals,  even 
the  very  lowest,  and  these  may  be  called  essentials  of  animal  life.  If  we 
go  a  step  further,  we  find  that  most  of  these  characteristic  properties 
and  functions  are  possessed  also  by  the  very  lowest  vegetable  structures, 
and  are  in  fact  the  characters  by  which  we  distinguish  living  from  not- 
living  matter;  they  are  essentials  or  phenomena  of  life  in  general.  Thus 
we  see  that  as  human  physiology,  which  treats  of  man  only,  is  a  part  of 
animal  physiology,  which  treats  of  the  functions  and  organization  of 
animals  in  general,  so  is  animal  physiology  but  a  part  of  the  wider 
science  of  Biology,  which  embraces  the  organization  and  manifestations 
of  all  living  things. 

Before  entering  upon  the  study  of  Human  physiology,  therefore,  it 
is  useful  and  even  necessary  to  devote  our  attention  for  a  little  while  to 
the  investigation  of  what  are  the  properties  and  functions  common  to  all 
living  matter,  and  how  they  are  manifested,  since  it  would  be  unwise  to 
attempt  to  comprehend  the  working  of  the  complex  machine  of  the  life 
of  man  without  some  knowledge  of  the  motive  power  in  its  simplest 
form. 

Living  matter,  in  its  most  elementary  form,  is  found  to  consist  of  a 
jelly-like  substance  which  is  now  generally  known  under  the  name  of 
Protoplasm. 

This  substance,  in  its  most  primitive  form,  and  in  minute  masses,  is 
found  undifferentiated  and  perfectly  homogeneous,  and  constitutes  the 
lowest  types  both  of  animal  and   vegetable  life  that  can  be  observed 
1 


2  HANDBOOK   OF    PHYSIOLOGY. 

under  the  microscope.  It  is  this  substance,  too,  which  forms  the  cells, 
of  which  even  the  most  complex  organism  has  been  proved  to  be  made 
up  and  from  which  it  has  been  developed.  Thus,  the  human  body  can 
be  shown  by  dissection  to  consist  of  various  dissimilar  parts,  bones,  mus- 
cles, brain,  heart,  lungs,  intestines,  etc.,  and  these,  on  more  minute 
examination,  are  found  to  be  composed  of  different  tissues,  such  as  epi- 
thelial, connective,  nervous,  muscular,  and  the  like.  Each  of  these  tis- 
sues is  made  up  of  cells  or  of  their  altered  equivalents.  Again,  we  are 
taught  by  Embryology,  the  science  which  treats  of  the  growth  and 
structure  of  organisms  from  their  first  coming  into  being,  that  the 
human  body,  made  up  of  all  these  dissimilar  structures,  commences  its 
life  as  a  minute  cell  or  ovum  about  one  one  hundred  and  twentieth  of  an 
inch  in  diameter,  consisting  of  a  spherical  mass  of  protoplasm,  in  the 
midst  of  which  was  contained  a  smaller  spherical  body  or  germinal  vesi- 
cle. The  phenomena  of  life  then  are  exhibited  in  cells,  whether  exist- 
ing alone  or  developed  into  the  organs  and  tissues  of  animals  and  plants. 
It  must  be  at  once  evident,  therefore,  that  a  correct  knowledge  of  the 
nature  and  activities  of  the  cell,  forms  the  very  foundation  of  physiology. 
Cells  are,  in  fact,  physiological  no  less  than  morphological  units. 

The  prime  importance  of  the  cell  as  an  element  of  structure  was  first 
established  by  the  researches  of  Schleiden,  and  his  conclusions,  drawn 
from  the  study  of  vegetable  histology,  were  at  once  extended  by 
Schwann  to  the  animal  kingdom.  The  earlier  observers  defined  a  cell 
as  a  more  or  less  spherical  body  limited  by  a  membrane,  and  containing 
a  smaller  body  termed  a  nucleus,  which  in  its  turn  incloses  one  or  more 
nucleoli.  Such  a  definition  applied  admirably  to  most  vegetable  cells, 
but  the  more  extended  investigation  of  animal  tissues  soon  showed  that 
in  many  cases  no  limiting  membrane  or  cell-wall  could  be  demonstrated. 

The  presence  or  absence  of  a  cell-wall,  therefore,  was  now  regarded 
as  quite  a  secondary  matter,  while  at  the  same  time  the  cell-substance 
came  gradually  to  be  recognized  as  of  primary  importance.  Many  of 
the  lower  forms  of  animal  life,  e.  g  ,  the  Rhizopoda,  were  found  to  con- 
sist almost  entirely  of  matter  very  similar  in  appearance  and  chemical 
composition  to  the  cell-substance  of  higher  forms;  and  this  from 
its  chemical  resemblance  to  flesh  was  termed  Sarcode  by  Dujardin. 
When  recognized  in  vegetable  cells  it  was  called  Protoplasm  by  Mulder, 
while  Remak  applied  the  same  name  to  the  substance  of  animal  cells. 
As  the  presumed  formative  matter  in  animal  tissues  it  was  termed  Blas- 
tema, and  in  the  belief  that,  wherever  found,  it  alone  of  all  substances 
has  to  do  with  generation  aud  nutrition,  Beale  has  named  it  Germinal 
matter  or  Bioplasm.  Of  these  terms  the  one  most  in  vogue  at  the  pres- 
ent day,  as  we  have  already  said,  is  Protoplasm,  and  inasmuch  as  all  life, 
both  in  the  animal  and  vegetable  kingdoms,  is  associated  with  proto- 
plasm, we  are  justified  in  describing  it,  with  Huxley,  as  the  "physical 
basis  of  life,"  or  simply  "  living  matter." 

A  cell  may  now  be  defined  as  a  nucleated  mass  of  protoplasm,"  of 
microscopic  size,  which  possesses  sufficient  individuality  to  have  a  life- 

1  In  the  human  body  the  colls  range  from  the  red  blood-cell  (rtsVo  m-)  to  the 
ganglion-cell  (jfo  in.). 


THE    PHENOMENA    <>K    LIFE.  A 

history  of  its  own.  Each  cell  goes  through  the  same  cycle  of  changes  as 
the  whole  organism,  though  doubtless  in  a  much  shorter  time.  Begin- 
ning with  its  origin  from  some  preexisting  cell,  it  grows,  produces  other 
eells,  and  finally  dies.  It  is  true  that  several  lower  forms  of  life  consist 
of  non-nucleated  protoplasm,  but  the  above  definition  holds  good  for  all 
the  higher  plants  and  animals. 

Hence  a  summary  of  the  manifestations  of  cell  life  is  really  an  ac- 
count of  the  vital  activities  of  protoplasm. 

Protoplasm. — Physically,  protoplasm  is  viscid,  varying  from  a 
semi-fluid  to  a  strongly  coherent  consistency.  Chemically,  living  proto- 
plasm is  an  extremely  unstable  albuminoid  substance,  insoluble  in  water. 
It  is  neutral  or  weakly  alkaline  in  reaction.  It  undergoes  heat  stiffening 
or  coagulation  at  about  130°  F.  (54.5°  C),  and  hence  no  organism  can 
live  when  its  own  temperature  is  raised  beyond  this  point. 

Many,  of  course,  can  exist  for  a  time  in  a  much  hotter  atmosphere, 
since  they  possess  the  means  of  regulating  their  own  temperature. 

Besides  the  coagulation  produced  by  heat,  protoplasm  is  coagulated 
and  therefore  killed  by  all  the  reagents  which  produce  this  change  in 
albumen  (see  Appendix).  If  protoplasm  be  subjected  to  chemical 
analysis,  the  chief  substances  of  which  it  is  found  to  consist  belong  to 
the  class  of  bodies  called  Proteids  or  albumins.  These  are  bodies  made 
up  of  the  chemical  elements  C.  H.  N.  0.  and  S.,  in  certain  slightly 
varying  proportions.  They  are  essential  to  the  formation  of  protoplasm, 
for  without  one  or  more  of  them,  protoplasm  cannot  exist.  Indeed  some 
would  put  this  still  more  shortly,  and  say  that  protoplasm  is  living  pro- 
teid.  Associated  with  proteids  as  an  esseutial,  is  a  certain  amount  of 
water;  but  there  are  other  bodies,  non-essential,  frequently  present,  and 
varying  under  different  circumstances;  such  as  glycogen,  starch,  cellulose, 
chlorophyll,  fats,  and  the  like. 

The  protoplasmic  substance  of  cells  may  undergo  more  or  less  essen- 
tial modifications:  thus,  in  fat  cells  we  may  have  oil,  or  fatty  crystals, 
occupying  nearly  the  whole  cell;  in  pigmeut  cells  we  fiud  granules  of 
pigment;  in  the  various  gland  cells  the  elements  of  their  secretions. 
Moreover,  the  original  protoplasmic  contents  of  the  cell  may  undergo  a 
gradual  chemical  change  with  advancing  age;  thus  the  protoplasmic 
cell-substance  of  the  deeper  layers  of  the  epidermis  becomes  gradually 
converted  into  keratin  as  the  cell  approaches  the  surface.  So,  too,  the 
original  protoplasm  of  the  embryonic  blood-cells  is  infiltrated  with  the 
haemoglobin  of  the  mature  colored  blood-corpuscle. 

The  vital  or  physiological  characters  of  protoplasm  are  seen  in  the 
performance  of  its  functions.  Many  of  these  qualities  are  exceedingly 
well  illustrated  in  the  microscopic  animal  called  the  Amoeba,  which  is  a 
monocellular  organism  found  chiefly  in  fresh  water,  but  also  in  the  sea 
and  in  damp  earth.  Under  the  same  term  no  doubt  more  than  one  kind 
of  organism  is  included,  but  at  any  rate  in  each  most  of  the  vital 
properties  of  protoplasm  may  well  be  studied.     They  are  as  follows: — 


HANDBOOK    OF    PHYSIOLOGY. 


1.  The  power  of  spontaneous  movement. — When  an  amoeba  is  observed! 
with  a  sufncientlv  high  power  of  the  microscope,  it  is  found  to  consist 
of  an  irregular  mass  of  protoplasm  distinguished   into  an  outer  dense 

layer  and  an  inner  more  fluid  mass.     If 
watched  for  a  minute  or  two  an  irregular 
projection  or  pseudopoclium  is  seen  to  be 
gradually  thrust  out  from  the  main  body 
and  retracted:  a  second  mass  is  then  pro- 
truded in  another  direction,  and  gradu- 
ally the  whole   protoplasmic   substance 
is,  as  it  were,  drawn  into  it.    The  Amoeba 
thus   comes  to   occupy  a  new  position, 
and  when  this  is  repeated  several  times  we  have  locomotion  in  a  definite 
direction,  together  with  a  continual  change  of  form.     These  movements, 
when  observed  in  other  cells,  such  as  the  colorless  blood- corpuscles  of 


Fig.   1.- -Amoebae. 


Fig.  2  —Human  colorless  blood-corpuscle,  showing  its  successive  changes  of  outline  within  ten 
minutes  when  kept  moist  on  a  warm  stage.    (Schofleld.) 

higher  animals  (Fig.  2),  in  the  branched  cornea  cells  of  the  frog  and 
elsewhere,  are  hence  termed  amoeboid. 

Other  illustrations  of  amoeboid  movement. — The  remarkable  motions 
of  pigment-granules  observed  in  the  branched  pigment-cells  of  the  frog's 
skin  by  Lister  are  probably  due  to  amoeboid  movement.  These  granules 
are  seen  at  one  time  distributed  uniformly  through  the  body  and 
branched  processes  of  the  cell,  while  under  the  action  of  various  stimuli 
(e.g.,  light  and  electricity)  they  collect  in  the  central  mass,  leaving  the 
branches  quite  colorless. 

Ciliary  action  must  be  regarded  as  only  a  special  variety  of  the  gen- 
eral motion  with  which  all  protoplasm  is  endowed. 

The  grounds  for  this  view  are  the  following  :  In  the  case  of  the 
Infusoria,  which  move  by  the  vibration  of  cilia  (microscopic  hair-like 
processes  projecting  from  the  surface  of  their  bodies)  it  has  been  proved 
that  these  are  simply  processes  of  their  protoplasm  protruding  through 
pores  of  the  investing  membrane,  like  the  oars  of  a  galley,  or  the  head 
and  legs  of  a  tortoise  from  its  shell:  certain  reagents  cause  them  to  be 
partially  retracted.  Moreover,  in  some  cases  cilia  have  been  observed 
to  develop  from,  and  in  others  to  be  transformed  into,  amoeboid  pro- 
cesses. 

In  the  hairs  of  the  stinging-nettle  and  Tradescantia  and  the  cells  of 
Vallisneria  and  Chara,  the  movement  of  protoplasm  can  be  marked  by 
the  movement  of  the  granules  nearly  always  imbedded  in  it.  For 
example,  if  part  of  a  hair  of  Tradescantia  (Fig.  3)  be  viewed  under  a  high 
magnifying  power,  streams  of  protoplasm  containing  crowds  of  granules 
hurrying  along,  like  the  foot  passengers  in  a  busy  street,  are  seen  flow- 


Fig.  3.— Cell  of  Tradescantia  drawn  at 
successive  intervals  of  two  minutes.  The 
cell-contents  consist  •>!'  a  central  mass  con- 
nected by  many  irregular  processes  to  a 
peripheral  film:  the  whole  forms  a  vacuo- 
lated mass  of  protoplasm,  which  is  continu- 
ally changing  its  shape.    (Schofield.) 


THE    PHENOMENA    OF    LIFE.  ** 

lug  steadily  in   definite  directions,  some   coursing  round    the  film  which 
lines  the  interior  of  the  cell-wall,  and  others  flowing  towards  or  away 
from  the  irregular  mass  in  the  centre  of  the  cell-cavity.     Many  of  these 
.streams  of  protoplasm  run    together 
into  larger  ones,  and  are  lost  in  the 
central  mass,  and  thus  ceaseless  vari- 
ations of  form  are  produced. 

2.  Irritability  and  the,  power  of 
response  to  stimuli. — Although  the 
movements  of  the  amoeba  have  been 
described  above  as  spontaneous,  yet 
they  may  be  increased  under  the  ac- 
tion of  various  stimuli,  and  if  the 
movement  have  ceased  for  a  time,  as 
is  the  case  if  the  temperature  be  low- 
ered beyond  a  certain  point,  it  may  be 
set  up  by   raising   the   temperature. 

Again,  contact  with  foreign  bodies,  gentle  pressure,  certain  salts,  and  elec- 
tricity, if  applied  to  the  amoeba,  produce  or  increase  the  movement.  It 
is,  therefore,  sensitive  or  irritable  to  stimuli,  and  shows  its  irritability 
by  movement  or  contraction  of  its  mass. 

The  effects  of  some  of  these  stimuli  may  be  thus  further  detailed: — 

1.  Changes  of  temperature, — Moderate  heat  acts  as  a  stimulant:  this 
is  readily  observed  in  the  activity  of  the  movements  of  a  human  colorless 
blood-corpuscle  when  placed  under  conditions  in  which  its  normal  tem- 
perature and  moisture  are  preserved.  Extremes  of  heat  and  cold  stop 
the  motions  entirely. 

2.  Mechanical  stimuli. — When  gently  squeezed  between  a  cover  and 
object-glass  under  proper  conditions,  a  colorless  blood-corpuscle  is  stimu- 
lated to  active  amoeboid  movement. 

3.  Nerve  influence. — By  stimulation  of  the  nerves  of  the  frog's  cornea, 
contraction  of  certain  of  its  branched  cells  has  been  produced. 

4.  Chemical  stimuli. — Water  generally  stops  amoeboid  movement,  and 
by  imbibitiou  causes  great  swelling  and  finally  bursting  of  the  cells.  In 
some  cases,  however  (myxomycetes),  protoplasm  can  be  almost  entirely 
dried  up,  and  is  yet  capable  of  renewing  its  motion  when  again  moist- 
ened. Dilute  salt-solution  and  many  dilute  acids  and  alkalies,  stimu- 
late the  movements  temporarily. 

Ciliary  movement  is  suspended  in  an  atmosphere  of  hydrogen  or 
carbonic  acid,  and  resumed  on  the  admission  of  air  or  oxygen. 

5.  Electrical. — Weak  currents  stimulate  the  movement,  while  Btrong 
currents  cause  the  corpuscles  to  assume  a  spherical  form  and  become 
motionless. 


3.  Nutritive  powers. — The  power  of  taking  in  food,  modifying  it. 
building  up  tissue  by  assimilating  it,  and  rejecting  what  in  not  assimi- 
lated. All  these  processes  take  place  in  the  amoeba.  They  are  effected 
by  its  simply  flowing  round  and  inclosing  within  itself  minute  organisms 


6  HANDBOOK    OF    PHYSIOLOGY. 

such  as  diatoms  and  the  like,  from  which  it  exti'acts  what  it  requires, 
and  then  rejects  or  excretes  the  remainder,  which  has  never  formed  part 
of  the  body,  by  withdrawing  itself  from  it.  The  assimilation  which  goes 
on  in  the  body  of  the  amoeba,  is  to  replace  waste  of  its  tissue  consequent 
upon  manifestation  of  energy. 

The  two  processes  of  waste  and  repair,  then,  go  on  side  by  side,  and  as 
long  as  they  are  equal  the  size  of  the  animal  remains  stationary.  If, 
however,  the  building  up  exceed  the  waste,  then  the  animal  grows  ;  if 
the  waste  exceed  the  repair,  the  animal  decays ;  and  if  decay  go  on  be- 
yond a  certain  point,  life  becomes  impossible,  so  the  animal  dies. 

Growth,  or  inherent  power  of  increasing  in  size,  although  essential  to 
our  idea  of  life,  is  not  confined  to  living  beings.  A  crystal  of  common 
salt,  or  of  any  other  similar  substance,  if  placed  under  appropriate  con- 
ditions for  obtaining  fresh  material,  will  grow  in  a  fashion  as  definitely 
characteristic  and  as  easily  to  be  foretold  as  that  of  a  living  creature.  It 
is,  therefore,  necessary  to  explain  the  distinctions  which  exist  in  this  re- 
spect between  living  and  lifeless  structures  ;  for  the  manner  of  growth 
in  the  two  cases  is  widely  different. 

Differences  between  living  and  lifeless  growth. — (1.)  The  growth  of  a 
crystal,  to  use  the  same  example  as  before,  takes  place  merely  by  addi- 
tions to  its  outside  ;  the  new  matter  is  laid  on  particle  by  particle,  and 
layer  by  layer,  and,  when  once  laid  on,  it  remains  unchanged.  In  a 
living  structure,  on  the  other  hand,  as,  for  example,  a  brain  or  a  muscle, 
where  growth  occurs,  it  is  by  addition  of  new  matter,  not  to  the  surface 
only,  but  throughout  every  part  of  the  mass. 

(2.)  All  living  structures  are  subject  to  constant  decay  ;  and  life  con- 
sists not,  as  once  supposed,  in  the  power  of  preventing  this  never-ceasing 
decay,  but  rather  in  making  up  for  the  loss  attendant  on  it  by  never- 
ceasing  repair.  Thus,  a  man's  body  is  not  composed  of  exactly  the  same 
particles  day  after  day,  although  to  all  intents  he  remains  the  same  in- 
dividual. Almost  every  part  is  changed  by  degrees  ;  but  the  change  is 
so  gradual,  and  the  renewal  of  that  which  is  lost  so  exact,  that  no  differ- 
ence may  be  noticed,  except  at  long  intervals  of  time.  A  lifeless  struc- 
ture, as  a  crystal,  is  subject  to  no  such  laws  ;  neither  decay  nor  repair  is 
a  necessary  condition  of  its  existence.  That  which  is  true  of  structure 
which  never  had  to  do  with  life  is  true  also  with  respect  to  those  which, 
though  they  are  formed  by  living  parts,  are  not  themselves  alive.  Thus, 
an  oyster-shell  is  formed  by  the  living  animal  which  it  incloses,  but  it  is 
as  lifeless  as  any  other  mass  of  inorganic  matter ;  and  in  accordance 
with  this  circumstance  its  growth  takes  place  layer  by  layer,  and  it  is  not 
subject  to  the  constant  decay  and  reconstruction  which  belong  to  the 
living.     The  hair  and  nails  are  examples  of  the  same  fact. 

(3.)  In  connection  with  the  growth  of  lifeless  masses  there  is  no  al- 
teration in  the  chemical  composition  of  the  material  which  is  taken  up 
and  added  to  the  previously  existing  mass.  For  example,  when  a  crystal 
of  common  salt  grows  on  being  placed  in  a  fluid  which  contains  the  same 
material,  the  properties  of  the  salt  are  not  changed  by  being  taken  out 
of  the  liquid  by  the  crystal  and  added  to  its  surface  in  a  solid  form. 
But  the  case  is  essentially  different  in  living  beings,  both  animal  and 
vegetable.  A  plant,  like  a  crystal,  can  only  grow  when  fresh  material  is 
presented  to  it ;  and  this  is  absorbed  by  its  leaves  and  roots  ;  and  animals 


THE    PHENOMENA    OF    LIFE. 


for  the  same  purpose  of  getting  new  matter  for  growth  and  nutrition, 
take  food  into  their  stomachs.  But  in  both  these  cases  the  materials  are 
much  altered  before  they  are  finally  assimilated  by  the  structures  they 
are  destined  to  nourish. 

(4.)  The  growth  of  all  living  things  has  a  definite  limit,  and  the  law 
which  governs  this  limitation  of  increase  in  size  is  so  invariable  that  we 
should  be  as  much  astonished  to  find  an  individual  plant  or  animal  with- 
out limit  as  to  growth  as  without  limit  to  life. 

4.  Reproductive  powers. — The  amoeba,  to  return  to  our  former  illus- 
tration, when  the  growth  of  its  protoplasm  has  reached  a  certain  point. 
manifests  the  power  of  reproduction,  by  splitting  up  into  (or  in  some 
other  way  producing)  two  or  more  parts,  each  of  which  is  capable  of  in- 
dependent existence.  The  new  amoeba?  manifest  the  same  properties  as 
their  parent,  perform  the  same  functions,  grow  and  reproduce  in  their 
turn.     This  cycle  of  life  is  being  continually  passed  through. 

In   more  complicated  structures  than  the  amoeba,    the  life  of  indi- 


Fig.  4.— Diagram  of  an  ovum  (a)  undergoing  segmentation. —In  (6)  it  has  divided  into  two  ;  in 
(c)  into  four  ;  and  in  (d)  the  process  has  ended  in  the  production  of  the  so-called  "  mulberry  mass." 
(Frey.) 

vidual  protoplasmic  cells  is  probably  very  short  in  comparison  with  that 
of  the  organism  they  compose  :  aud  their  constant  decay  and  death 
necessitate  constant  reproduction. 

The  mode  in  which  this  takes  place  has  long  been  the  subject  of 
great  controversy. 

It  is  now  very  generally  believed  that  every  cell  is  descended  from 
some  jjre-existing  (mother-)  cell.  This  derivation  of  cells  from  cells 
takes  place  by  (1)  gemmation,  or  (2)  fission  or  division. 

(1)  Gemmation. — This  method  has  not  been  observed  in  the  human 
body  or  the  higher  animals,  and  therefore  requires  but  a  passing  notice. 
It  consists  essentially  in  the  budding  off  and  separating  of  a  portion  of 
the  parent  cell. 

(2)  Fission  or  Division. — As  examples  of  reproduction  by  fission,  we 
may  select  the  ovum,  the  blood  cell,  and  cartilage  cells. 

In  the  frog's  ovum  (in  which  the  process  can  be  most  readily  ob- 
served) after  fertilization  has  taken  place,  there  is  first  some  amoeboid 
movement,  the  oscillation  gradually  increasing  until  a  permanent  dimple 
appears,  which  gradually  extends  into  a  furrow  running  completely 
round  the  spherical  ovum,  and  deepening  until  the  entire  yelk-mass  is 
divided  into  two  hemispheres  of  protoplasm  each  containing  a  nucleus 
(Fig.  4,  b).  This  process  being  repealed  by  the  formation  of  a  second 
furrow  at  right  angles  to  the  first,  we  have  four  cells  produced  (r)  :  this 


s 


HANDBOOK    OF    PHYSIOLOGY, 


subdivision  is  carried  on  till  the  ovum  has  been  divided  by  segmentation 
into  a  mass  of  cells  (mulberry-mass)  (d)  out  of  which  the  embryo  is  de- 
veloped. Segmentation  is  the  first  step  in  the  development  of  all  the 
higher  animals,  including  man. 

Multiplication  by  fission  has  been  observed  in  the  colorless  blood- 
cells  of  many  animals.     In  some  cases  (Fig.   5),  the  process  has  been 


®    ®    0     @ 


Fig.  5.— Blood-corpuscle  from  a  young  deer  embryo,  multiplying  by  fission.    (Frey.) 

seen  to  commence  with  the  nucleolus  which  divides  within  the  nucleus. 
The  nucleus  then  elongates,  and  soon  a  well-marked  constriction  occurs, 
rendering  it  hour-glass  shaped,  till  finally  it  is  separated  into  two  parts, 
which  gradually  recede  from  each  other;  the  same  process  is  repeated  in 
the  cell-substance,  and  at  length  we  have  two  cells  produced  which  by 
rapid  growth  soon  attain  the  size  of  the  parent  cell  {direct  division). 
In  some  cases  there  is  a  primary  fission  into  three  instead  of  the  usual 
two  cells. 

In  cartilage  (Fig,  6),  a  process  essentially  similar  occurs,  with  the 


Fig.  ti.— Diagram  of  a  cartilage  cell  undergoing  fission  within  its  capsule.— The  process  of  divi- 
sion is  represented  as  commencing  in  the  nucleolus,  extending  to  the  nucleus,  and  at  length  involv- 
ing the  body  of  the  cell.    (Frey.) 

exception  that  (as  in  the  ovum)  the  cells  produced  by  fission  remain  in 
the  original  capsule,  and  in  their  turn  undergo  division,  so  that  a  large 
number  of  cells  are  sometimes  observed  within  a  common  envelope. 
Tin's  process  of  fission  within  a  capsule  has  been  by  some  described  as  a 
separate  method,  under  the  title  "  endogenous  fission,"  but  there  seems 
to  be  no  sufficient  reason  for  drawing  such  a  distinction. 

It  is  important  to  observe  that  fission  is  often  accomplished  with 
great  rapidity,  the  whole  process  occupying  but  a  few  minutes,  hence 
i  he  comparative  rarity  with  which  cells  are  seen  in  the  act  of  dividing. 

Indirect  cell  division. — In  certain  and  numerous  cases,  the  division 
of  cells  does  not  take  place  by  the  simple  constriction  of  their  nuclei  and 


THE    PHENOMENA    OF    I. ill:.  b 

surrounding  protoplasm  into  two  parts  as  above  described  (direct  divi- 
sion), but  is  preceded  by  complicated  changes  in  their  nuclei  (karyoki- 
nesis).  These  changes  consist  in  a  gradual  re-arrangement  of  the  intra- 
nuclear network  of  each  nucleus  (see  p.  17),  until  two  nuclei  are  formed 
similar  in  all  respects  to  the  original  one.  The  nucleus  in  a  resting 
condition,  i.e.,  before  any  changes  preceding  division  occur,  consists  of 
a  very  close  meshwork-of  fibrils,  which  stain  deeply  in  carmine,  embed- 
ded in  protoplasm,  which  does  not  possess  this  property,  the  whole 
nucleus  being  contained  in  an  envelope.  The  first  change  consists  of  a 
slight  enlargement,  the  disappearance  of  the  envelope,  and  the  increased 
definition  and  thickness  of  the  nuclear  fibrils,  which  are  also  more  sepa- 
rated than  they  were,  and  stain  better.  This  is  the  stage  of  convolution 
(Fig.  7,  B,  c).     The  next  step  in  the  process  is  the  arrangement  of  the 


Fig.  7.—  Karyokinesis.  a,  ordinary  nucleus  of  a  columnar  epithelial  cell ;  b,  c,  the  same  nu- 
cleus in  thestage  of  convolution  ;  d.  the  wreath  or  rosette  form  :  e,  the  aster  or  single  star  ;  f.  a  nu- 
clear spindle  from  the  Desceiuet's  endothelium  of  the  frog's  cornea  ;  a,  h,  I,  diaster  ;  k,  two  daugh- 
ter nuclei.     (Klein. ) 

fibrils  into  some  definite  figure  by  an  alternate  looping  in  and  out  around 
a  central  space,  by  which  means  the  rosette  or  wreath  stage  (Fig.  7,  r>) 
is  reached.  The  loops  of  the  rosette  next  become  divided  at  the  peri- 
phery, and  their  central  points  become  more  angular,  so  that  the  fibrils, 
divided  into  portions  of  about  equal  length,  are,  as  it  were,  doubled  at 
an  acute  angle,  and  radiate  V-shaped  from  the  centre,  forming  a  star 
(aster)  or  wheel  (Fig.  7,  E),  or  perhaps  from  two  centres,  in  which  case  a 
double  star  (diaster)  results  (Fig.  7,  G,  H,  and  i).  After  remaining 
almost  unchanged  for  some  time,  the  V-shaped  fibres  being  first  re-ar- 
ranged in  the  centre,  side  by  side  (angle  outwards),  tend  to  separate  into 
two  bundles,  which  gradually  assume  position  at  either  pole.  From  these 
groups  of  fibrils  the  two  nuclei  of  the  new  cells  are  formed  (daughter 
nuclei)  (Fig.  ].  k),  and  the  changes  they  pass  through  before  reaching 
the  resting  condition  are  exactly  those  through  which  the  original  nu- 
cleus (mother  nucleus)  has  gone,  but  in  a  reverse  order,  viz.,  the  star. 
the  rosette,  and  the  convolution.  During  or  shortly  after  the  forma- 
tion of  the  daughter  nuclei  the  cell  itself  becomes  constricted  and  then 
divides  in  a  line  about  midway  between  them. 

5.  Decay  mill  death  of  cells.  —There  are  two  chief  ways  in  which  the 
comparatively  brief  existence  of  cells  is  brought  to  an  end:  (1)  Me- 
chanical abrasion.  ("?)  Chemical  transformation. 


10  HANDBOOK    OF    PHYSIOLOGY. 

1.  The  various  epithelia  (p.  19)  furnish  abundant  examples  of 
mechanical  abrasion.  As  it  approaches  the  free  surface  the  cell  be- 
comes more  and  more  flattened  and  scaly  in  form  and  more  horny  in 
consistence,  till  at  length  it  is  simply  rubbed  off.  Hence  we  find  epithe- 
lial cells  in  the  mucus  of  the  mouth,  intestine,  and  genito-urinary  tract. 

2.  In  the  case  of  chemical  transformation  the  cell-contents 
undergo  a  degeneration  which,  though  it  may  be  pathological,  is  very 
often  a  normal  process.  Thus  we  have  (a.)  fatty  metamorphosis  pro- 
ducing oil-globules  in  the  secretion  of  milk,  fatty  degeneration  of  the 
muscular  fibres  of  the  uterus  after  birth  of  the  foetus,  and  of  the  cells  of 
the  Graafian  follicle  giving  rise  to  the  '*  corpus  luteum.*'  (See  chapter 
on  Generation.)  (b.)  Pigmentary  degeneration  from  deposit  of  pig- 
ment, as  in  the  epithelium  of  the  air- vesicles  of  the  lungs,  (c. )  Calca- 
reous degeneration,  which  is  common  in  the  cells  of  many  cartilages. 

Differences  betiveen  Plants  and  Animals. 

Having  now  considered  somewhat  at  length  the  vital  properties  of 
protoplasm,  as  shown  in  cells  of  vegetable  as  well  as  animal  organisms, 
we  are  now  in  a  position  to  discuss  the  question  of  the  differences  between 
plants  and  animals.  It  might  at  the  outset  of  our  inquiry  have  seemed 
an  unnecessary  thing  to  recount  the  very  great  distinctions  which  exist 
between  an  animal  and  a  vegetable,  but,  however  great  these  may  be 
between  the  higher  animals  and  plants,  yet  in  the  lowest  of  them  the 
distinctions  are  much  less  obvious. 

(1.)  Perhaps  the  most  essential  distinction  is  the  power  which  vege- 
table protoplasm  possesses  of  being  able  to  build  up  new  albuminous 
material  out  of  such  chemical  bodies  as  ammonium  salts,  carbonic  acid 
gas  and  water,  together  with  mineral  sulphates  and  phosphates.  By 
means  of  their  green  coloring  matter,  chlorophyl — a  substance  almost 
exclusively  confined  to  the  vegetable  kingdom — plants  are  capable  of 
decomposing  the  carbonic  acid  gas,  which  they  absorb  by  their  leaves. 
The  result  of  this  chemical  action,  which  occurs  only  under  the  influence 
of  light,  is,  so  far  as  the  carbonic  acid  is  concerned,  the  fixation  of 
carbon  in  the  plant  structures  and  the  exhalation  of  oxygen.  The  carbon 
thus  obtained  becomes  combined  with  the  elements  of  water  absorbed 
by  the  roots,  to  form  starch.  By  the  re-arrangement  of  the  elements 
composing  this  body,  with  the  addition  of  nitrogen  and  sulphur  derived 
from  nitrates  and  sulphates  of  the  soil,  vegetable  protoplasm  can  con- 
struct albumen.  Animal  protoplasm  is  incapable  of  thus  using  such 
substances  and  never  exhales  oxygen  as  a  product  of  decomposition.  It 
must  have  ready-formed  albuminous  food  in  order  to  live. 

The  power  of  living  upon  albuminous  as  well  as  non-albuminous 
matter  is  less  decisive  of  an  animal  nature;  inasmuch  as  fungi  and  some 
other  parasitic  plants  derive  their  nourishment  in  part  from  the  former 
source. 

(2.)  There  is,  commonly,  a  difference  in  general  chemical  composition 


THE    PHENOMENA    OF    LIFE.  11 

between  vegetables  and  animals,  even  in  their  lowest  forms;  for  associ- 
ated with  the  protoplasm  of  the  former  is  a  considerable  amount  of 
cellulose,  a  substance  closely  allied  to  starch  and  containing  carbon, 
hydrogen,  and  oxygen  only.  The  presence  of  cellulose  in  animals  is 
much  more  rare  than  in  vegetables,  but  there  are  many  animals  in  which 
traces  of  it  may  be  discovered,  and  some,  the  Ascidians,  in  which  it  is 
found  in  considerable  quantity.  The  presence  of  starch  in  vegetable 
cells  is  very  characteristic,  though  not  distinctive,  and  a  substance,  gly- 
cogen, nearly  allied  in  composition  to  cellulose,  is  very  common  in  the 
organs  and  tissues  of  animals. 

(3.)  Inherent  power  of  movement  is  a  quality  which  we  so  commonly 
consider  an  essential  indication  of  animal  nature,  that  it  is  difficult  at 
first  to  conceive  it  existing  in  any  other.  The  capability  of  simple  mo- 
tion is  now  known,  however,  to  exist  in  so  many  vegetable  forms,  that  it 
can  no  longer  be  held  as  an  essential  distinction  between  them  and  ani- 
mals, and  ceases  to  be  a  mark  by  which  the  one  can  be  distinguished 
from  the  other.  Thus  the  zoospores  of  many  of  the  Cryptogamia  exhibit 
ciliary  or  amoeboid  movements  (p.  4)  of  a  like  kind  to  those  seen  in 
amoeba?;  and  even  among  the  higher  order  of  plants,  many,  e.g.,  Dioncea 
Muscipula  (Venus's  fly-trap),  and  Mimosa  sensitiva  (Sensitive  plant), 
exhibit  such  motion,  either  at  regular  times,  or  on  the  application  of 
external  irritation,  as  might  lead  one,  were  this  fact  taken  by  itself,  to 
regard  them  as  sentient  beings.  Inherent  power  of  movement,  then, 
although  especially  characteristic  of  animal  nature,  is,  when  taken  by 
itself,  no  proof  of  it. 

(4.)  The  presence  of  a  digestive  canal  is  a  very  general  mark  by 
which  an  animal  can  be  distinguished  from  a  vegetable.  But  the  lowest 
animals  are  surrounded  by  material  that  they  can  take  as  food,  as  a  plant 
is  surrounded  by  an  atmosphere  that  it  can  use  in  like  manner.  And 
every  part  of  their  body  being  adapted  to  absorb  and  digest,  they  have  no 
need  of  a  special  receptacle  for  nutrient  matter,  and  accordingly  have 
no  digestive  canal.     This  distinction  then  is  not  a  cardinal  one. 

It  would  be  tedious  as  well  as  unnecessary  to  enumerate  the  chief 
distinctions  between  the  more  highly  developed  animals  and  vegetables. 
They  are  sufficiently  apparent. 

In  passing,  it  maybe  well  to  point  out  the  main  distinctions  betiuecn 
animal  and  vegetable  cells. 

It  has  been  already  mentioned  that  in  animal  cells  an  envelope  or 
cell-wall  is  by  no  means  always  present.  In  adult  vegetable  cells,  on  the 
other  hand,  a  well-defined  cellulose  wall  is  highly  characteristic;  this,  it 
should  be  remembered,  is  non-nitrogenous,  and  thus  differs  chemically 
as  well  as  structurally  from  the  contained  mass. 

Moreover,  in  vegetable  cells  (Fig.  8,  b),  the  protoplastic  contents  of 
the  cell  fall  into  two  subdivisions:  (1)  a  continuous  film  which  lines  the 


12 


HANDBOOK    OF    PHYSIOLOGY. 


interior  of  the  cellulose  wall;  and  (2)  a  reticulate  mass  containing  the 
nucleus  and  occupying  the  cell-cavity;  its  interstices  are  filled  with  fluid. 
In  young  vegetable  cells  such  a  distinction  does  not  exist;  a  finely  gran- 
ular protoplasm  occupies  the  whole  cell-cavity  (Fig.  8,  a). 


Fig.  8. — fA)  Young  vegetable  cells,  showing  cell-cavity  entirely  filled  with  granular  protoplasm 
inclosing  a  large  oval  nucleus,  with  one  or  more  nucleoli,  (b)  Older  cells  from  same  plant,  show- 
ing distinct  cellulose-wall  and  vacuolation  of  protoplasm. 

Another  striking  difference  is  the  frequent  presence  of  a  large  quantity 
of  intercellular  substance  in  animal  tissues,  while  in  vegetables  it  is  com- 
paratively rare,  the  requisite  consistency  being  given  to  their  tissues  by 
the  tough  cellulose  walls,  often  thickened  by  deposits  of  lignin.  As  an 
example  of  the  manner  in  which  this  end  is  attained  in  animal  tissues, 
may  be  mentioned  the  deposition  of  lime-salts  in  a  matrix  of  intercellu- 
lar substance  in  ossification. 

Morphological  Development  and  Division  of  Functions. 

As  we  proceed  upwards  in  the  scale  of  life  from  monocellular  organ- 
isms, we  find  that  another  phenomenon  is  exhibited  in  the  life  history  of 
the  higher  forms,  namely,  that  of  Development.  An  amceba  comes  into 
being  derived  from  a  previous  amoeba;  it  manifests  the  properties  and 
performs  functions  of  life  which  have  been  already  enumerated ;  it  grows, 
it  reproduces  itself,  whereby  several  amoebae  result  in  place  of  one,  and 
it  dies,  but  it  can  scarcely  be  said  to  develop  unless  the  formation  of  a 
nucleus  can  be  so  considered.  In  the  higher  organisms,  however,  it  is 
different;  they,  indeed,  begin  as  a  single  cell,  but  this  cell  on  its  division 
and  subdivision  does  not  form  so  many  different  organisms,  but  possesses 
the  material  from  which,  by  development,  the  completed  and  perfected 
whole  is  to  be  derived.  Thus,  from  the  spherical  ovum,  or  germ,  which 
forms  the  starting-point  of  animal  life,  and  which  consists  of  a  proto- 
plasmic cell  with  a  nucleus  and  nucleolus  (see  Fig.  4),  in  a  comparatively 
short  time,  by  the  process  of  segmentation  which  has  been  already  men- 
tioned, a  complete  membrane  of  cells,  polyhedral  in  shape  from  mutual 
pressure,  called  the  blastoderm,  is  formed,  and  this  speedily  divides  into 
two  and  then  into  three  layers,  chiefly  from  the  rapid  proliferation  of  the 
cells  of  the  first  single  layer.  These  layers  are  called  the  epiblast,  the 
mesoblast,  and  the  hypoblast. 


Til?:    PHENOMENA    <>F    LIFE. 


13 


It  is  found  in  the  further  development  of  the  animal  that  from  each 
of  these  layers  is  produced  a  very  definite  part  of  its  completed  body. 
For  example,  from  the  cells  of  the  epiblast,  are  derived,  among  other 
structures,  the  skin  aiid  the  central  nervous  system;  from  the  mesoblast 
is  derived  the  flesh  or  muscles  of  the  body,  and  from  the  hypoblast,  the 
epithelium  of  the  alimentary  canal  and  some  of  the  chief  glands. 

From  the  epiblast  are  ultimately  developed  the  superficial  skin  or 
epidermis  and  its  various  appendages,  also  the  central  or  cerebro-spinal 
nerve  centres,  the  sensorial  epithelium  of  the  organs  of  special  sense  (the 
eye,  the  ear,  the  nose),  and  the  epithelium  of  the  mouth  and  salivary 
glands. 

From  the  hypoblast  is  developed  the  epithelium  of  the  whole  diges- 
tive canal,  together  with  that  lining  the  ducts  of  all  the  glands  which 
open  into  it  ;  also  the  glandular  parenchvma  of  the  glands  {e.g.,  liver 
and  pancreas)  connected  with  it,  and  the  epithelium  of  the  respiratoiy 
tracfc. 


Fig.  9.— Transverse  section  through  embryo  chick  (26  hours),  a,  epiblast ;  6,  mesoblast  ;  c,  hy- 
poblast ;  d,  central  portion  of  mesoblast,  which  is  here  fused  with  epiblast ;  e,  primitive  groove  ; 
/,  dorsal  ridge.    (Klein.) 

From  the  mesoblast  are  derived  all  the  tissues  aud  organs  of  the  body 
intervening  between  these  two,  the  whole  group  of  the  connective  tissues, 
the  muscles  and  the  cerebro-spinal  and  sympathetic  nerves,  with  the 
vascular  and  genito-urinary  systems,  and  all  the  digestive  canal,  with  its 
various  appendages,  with  the  exception  of  the  lining  epithelium  above 
mentioned. 

It  is  obvious  that  these  tissues  and  organs  exhibit  in  a  varying  degree 
the  primary  properties  of  protoplasm.  The  muscles,  for  example,  de- 
rived from  certain  cells  of  the  mesoblast  are  highly  contractile  and  re- 
spond to  stimuli  readily,  but  they  have  little  to  do  with  digestion  except 
indirectly,  and  again,  the  cells  of  the  liver,  although  doubtless  contrac- 
tile to  a  certain  extent,  yet  have  secretion  and  digestion  for  their  chief 
functions. 

Thus  we  see  development  in  two  directions  going  on  side  by  side.  It 
speedily  becomes  necessary  for  the  organism  to  depute  to  different 
groups  of  cells,  or  their  equivalents  (i.e.,  to  the  tissues  or  organs  to 
which  they  give  rise),  special  functions,  so  that  the  various  functions 


14  HANDBOOK    OF    PHYSIOLOGY. 

which  the  original  cell  may  be  supposed  to  discharge,  and  the  various 
properties  it  may  be  supposed  to  possess,  are  divided  up  among  various 
groups  of  resulting  cells.  The  work  of  each  group  is  specialized.  As  a 
result  of  this  division  of  labor,  as  it  is  called,  these  functions  and  prop- 
erties are,  as  might  be  expected,  developed,  and  made  more  perfect,  and 
the  tissues  and  organs  arising  from  each  group  of  cells  are  developed  also, 
with  a  view  to  the  more  convenient  and  effective  exercise  of  their  func- 
tions and  employment  of  their  properties.  It  would  be  out  of  place 
here  to  discuss  the  question  as  to  the  exact  manner  in  which  a  property 
or  function,  rudimentary  in  a  low  form  of  animal  life,  is  found  to  be 
nighly  developed  as  we  pass  up  the  series  ;  neither  is  it  our  province  to 
discuss  the  very  complicated  subject  of  the  relationship  of  man  to  other 
animals,  and  of  these  to  one  another. 

Having  now  briefly  indicated  the  close  connection  which  exists  be- 
tween Human  physiology  and  Biology  in  general,  we  are  better  prepared 
to  commence  the  study  of  the  former  as  constituting  a  part  of  a  great 
whole. 

The  next  two  chapters  will  be  devoted  to  a  consideration  of  the 
minute  structure,  or  the  histology  (ifftos,  a  tissue  or  web)  of  epithelium 
and  the  connective  tissues. 


CHAPTER   II. 

THE  STRUCTURE  OF  THE  ELEMENTARY  TISSUES. 

The  cells  of  the  body  are  described  in  various  ways  ;  for  example,  ac- 
cording to  their  shape,  situation,  contents,  origin  and  functions. 

(a.)  Their  shape  varies: — Starting  from  the  spherical  or  spheroidal 
(Fig.  10,  a)  as  the  typical  form  assumed  by  a  free  cell,  we  find  this  altered 
to  a  polyhedral  shape  when  the  pressure  on  the  cells  in  all  directions  is 
nearly  the  same  (Fig.  10,  b). 

Of  this,  the  primitive  segmentation-cells  may  afford  an  example. 

The  discoid  shape  is  seen  in  blood-cells  (Fig.  10,  c),  and  the  scale-like 
form  in  superficial  epithelial  cells  (Fig.  10,  d).  Some  cells  have  a  jugged 
outline  (prickle-cells)  (Fig.  27). 

Cylindrical ',  conical,  or  prismatic  cells  occur  in  the  deeper  layers  of 
laminated  epithelium,  and  the  simple  cylindrical  epithelium  of  the  in- 
testine and  many  glaud  ducts.  Such  cells  may  taper  off  at  one  or  both 
ends  into  fine  processes,  in  the  former  case  being  caudate,  in  the  latter 
fusiform  (Fig.  11).  They  may  be  greatly  elongated  so  as  to  become 
fibres.     Ciliated  cells  (Fig.  10,  d)  must  be  noticed  as  a  distinct  variety  : 


®B(D 


Fig.  10.— Various  formsof  cells,    a.  Spheroidal,  showing  nucleus  and  nucleolus  ;  ft.  Polyhedral ; 
c.  Discoidal  (blood  cells)  ;  d.  Scaly  or  squamous  (epithelial  cells). 


they  possess,  but  only  on  their  free  surfaces,  hair-like  processes  (cilia). 
These  vary  immensely  in  size,  and  may  even  exceed  in  length  the  cell 
itself.  Finally,  we  have  the  branched  or  stellate  cells,  of  which  the  large 
nerve-cells  of  the  spinal  cord,  and  the  connective  tissue  corpuscle  are 
typical  examples  (Fig.  11,  e).  In  these  cells  the  primitive  branches  by 
secondary  branching  may  give  rise  to  an  intricate  network  of  processes. 

(b.)  According  to  their  situation  in  the  tissues  cells  are  known  as 
epithelial,  connective  tissue  cells,  blood  cells,  glandular,  and  the  like. 

(c.)  According  to  their  contents,  they  are  called  fat  cells  when  their 
protoplasm  contains  an  excess  of  fat,  pigment  cells  when  it  contains  pig- 
ment ;  colored,  when  their  protoplasm  is  infiltrated  with  a  coloring 
matter,  as  haemoglobin. 


16 


HANDBOOK    OF    PHYSIOLOGY. 


Id.)  According  to  their  functions,  they  are  called  secreting,  protec- 
tive, sensitive,  contractile,  etc. 

(e.)  According  to  their  origin,  they  are  named  epiblastic,  mesoblastic 
and  hypoblastic. 

Nearly  all  cells  at  some  period  of  their  existence  possess  nuclei.  As 
has  been  incidentally  suggested,  the  origin  of  a  nucleus  in  a  cell  is  the 


Fig.  11.— Various  forms  of  cells,    a.  Cylindrical  or  columnar  ;  b.   Caudate  ;    c.  Fusiform  ;   d. 
Ciliated  (from  trachea)  ;  e.  Branched,  stellate. 

first  trace  of  the  differentiation  of  protoplasm.  The  existence  of  nuclei 
was  first  pointed  out  in  the  year  1833  by  Robert  Brown,  who  observed 
them  in  vegetable  cells.  They  are  either  small  transparent  vesicular 
bodies  containing  one  or  more  smaller  particles  (nucleoli),  or  they  are 


Fig.  18.— Ca.^  Colorless  blond-corpuscle  showing  intra  cellular  network  of  Heitzmann,  and  two 
nuclei  with  intra  nuclear  network  (Klein  and  Noble  Smith',  (b  )  Colored  blood-corpuscle  showing 
intra- cellular  network  of  fibrils  (Heitzmann).  Also  oval  nucleus  composed  of  limiting  membrane 
and  fine  intranuclear  network  of  fibrils,     x  800.    (Klein  and  Noble  Smith.) 

semi-solid  masses  of  protoplasm  always  in  the  resting  condition  bounded 
by  a  well-defined  envelope.  In  their  relation  to  the  life  of  the  cell  they 
are  certainly  hardly  second  in  importance  to  the  protoplasm  itself,  and 
thus  Beale  is  fully  justified  in  comprising  both  under  the  term  "germi- 
nal matter."  They  exhibit  their  vitality  by  initiating,  in  the  majority 
of  cases,  the  process  of  division  of  the  cell  into  two  or  more  cells  (fission) 
by  first  themselves  dividing.  Distinct  observations  have  been  made, 
showing  that  spontaneous  changes  of  form  may  occur  in  nuclei  as  also  in 
nucleoli. 


THE    STRUCTURE    OF    THE    ELEMENTARY    TISSUES.  Ii 

Histologists  have  long  recognized  nuclei  by  two  important  characters: 

(1.)  Their  power  of  resisting  the  action  of  various  acids  and  alkalies, 
particularly  acetic  acid,  by  which  their  outline  is  more  clearly  denned, 
and  they  are  rendered  more  easily  visible.  This  indicates  some  chemi- 
cal difference  between  the  protoplasm  of  the  cell  and  nuclei,  as  the  for- 
mer is  destroyed  by  these  reagents. 

(2.)  Their  quality  of  staining  in  solutions  of  carmine,  hematoxylin, 
etc.  Nuclei  are  most  commonly  oval  or  round,  and  do  not  generally 
conform  to  the  diverse  shapes  of  the  cells;  they  are  altogether  less  vari- 
able elements  than  cells,  even  in  regard  to  size,  of  which  fact  one  may 
see  a  good  example  in  the  uniformity  of  the  nuclei  in  cells  so  multiform 
as  those  of  epithelium.  But  sometimes  nuclei  appear  to  occupy  the 
whole  of  the  cell,  as  is  the  case  in  the  lymph  corpuscles  of  lymphatic 
glands,  and  in  some  small  nerve  cells. 

Their  position  in  the  cell  is  very  variable.  In  many  cells,  especially 
where  active  growth  is  progressing,  two  or  more  nuclei  are  present. 

Minute  structure  of  cells. — The  protoplasm  which  forms  the  body  as 
well  as  that  which  forms  the  nuclei  of  cells  has  been  shown  in  many 
varieties  of  cells,  e.g.,  the  colorless  blood-corpuscles,  epithelial  cells, 
connective-tissue  corpuscles,  nerve-cells,  to  be  made  up  of  a  network  of 
very  fine  fibrils,  the  meshes  of  which  are  occupied  by  a  hyaline  intersti- 
tial substance  (Heitzmamvs  network)  (Fig.  12).  At  the  nodes,  where 
the  fibrils  cross,  are  little  swellings,  and  these  are  the  objects  described 
as  granules  by  the  older  observers ;  but  in  the  body  of  some  cells,  e.g., 
colorless  blood- corpuscles,  there  are  real  granules,  which  appear  to  be 
quite  free  and  unconnected  with  the  intra-cellular  network. 

Modes  of  connection. — Cells  are  connected  together  to  form  tissues  in 
various  ways. 

(1)  By  means  of  a  cementing  intercellular  substance.  This  is  prob- 
ably always  present  as  a  transparent,  colorless,  viscid,  albuminous  sub- 
stance, even  between  the  closely  apposed  cells  of  epithelium,  while  in 
the  case  of  cartilage  it  forms  the  main  bulk  of  the  tissue,  and  the  cells 
only  appear  as  imbedded  in,  not  as  cemented  by,  the  intercellular  sub- 
stance. This  intercellular  substance  may  be  either  homogeneous  or 
fibrillated.  In  many  cases  {e.g.,  the  cornea)  it  can  be  shown  to  contain 
a  number  of  irregular  branched  cavities,  which  communicate  with  each 
other,  and  in  which  branched  cells  lie  :  through  these  branching  spaces 
nutritive  fluids  can  find  their  way  into  the  very  remotest  parts  of  a  non- 
vascular tissue. 

As  a  special  variety  of  intercellular  substance  must  be  mentioned  the 

basement  membrane  (membrana  propria)  which  is  found  at  the  base  of 

the  epithelial  cells  in  most  mucous  membranes,   and  especially  as  an 

investing  tunic   of  gland  follicles  which   determines  their  shape,  and 

2 


18  HANDBOOK    OF  PHYSIOLOGY. 

which  may  persist  as  a  hyaline  saccule  after  the  gland-cells  haye  all 
been  discharged. 

(2)  By  anastomosis  of  their  processes.  This  is  the  usual  way  in  which 
stellate  cells,  e.  g.,  of  the  cornea,  are  united  ;  the  individuality  of  each 
cell  is  thus  to  a  great  extent  lost  by  its  connection  with  its  neighbors  to 
form  a  reticulum ;  as  an  example  of  a  network  so  produced  we  may  cite 
the  stroma  of  lymphatic  glands. 

Sometimes  the  branched  processes  breaking  up  into  a  maze  of  minute 
fibrils,  adjoining  cells  are  connected  by  an  intermediate  reticulum  ;  this 
is  the  case  in  the  nerve-cells  of  the  spinal  cord. 

Derived  tissue-elements. — Besides  the  Cell,  which  may  be  termed  the 
primary  tissue-element,  there  are  materials  which  may  be  termed  secon- 
dary or  derived  tissue-elements.  Such  are  Intercellular  substance, 
Fibres,  and  Tubules. 

a.  Intercellular  substance  is  probably  in  all  cases  directly  derived 
from  the  cells  themselves.  In  some  cases  (e.  g.,  cartilage),  by  the  use 
of  reagents  the  cementing  intercellular  substance  is,  as  it  were,  analyzed 
into  various  masses,  each  arranged  in  concentric  layers  around  a  cell  or 
group  of  cells,  from  which  it  was  probably  derived  (Fig.  46). 

/?.  Fibres. — In  the  case  of  the  crystalline  lens,  and  of  muscle  both 
striated  and  non-striated,  each  fibre  is  simply  a  metamorphosed  cell:  in 
the  case  of  the  striped  fibre  the  elongation  being  accompanied  by  a  mul- 
tiplication of  the  nuclei. 

The  various  fibres  and  fibrilla?  of  connective  tissue  result  from  a  grad- 
ual transformation  of  an  originally  homogeneous  intercellular  substance. 
Fibres  thus  formed  may  undergo  great  chemical  as  well  as  physical 
transformation:  this  is  notably  the  case  with  yellow  elastic  tissue,  in 
which  the  sharply  defined  elastic  fibres,  possessing  great  power  of  resis- 
tance to  reagents,  contrast  strikingly  with  the  homogeneous  matter  from 
which  they  are  derived. 

y.  Tubules,  such  as  the  capillary  blood-vessels,  which  were  originally 
supposed  to  consist  of  a  structureless  membrane,  have  now  been  proved 
to  be  composed  of  flat,  thin  cells,  cohering  along  their  edges. 

With  these  simple  materials  the  various  parts  of  the  body  are  built 
up;  the  more  elementary  tissues  being,  so  to  speak,  first  compounded  of 
them;  while  these  tissues  are  variously  mixed  and  interwoven  to  form 
more  intricate  combinations. 

Thus  are  constructed  epithelium  and  its  modifications,  the  connec- 
tive tissues,  the  fibres  of  muscle  and  nerve,  etc. ;  and  these,  again,  with 
the  more  simple  structures  before  mentioned,  are  used  as  materials 
wherewith  to  form  arteries,  veins,  and  lymphatics,  secreting  and  vascu- 
lar glands,  lungs,  heart,  liver,  and  other  parts  of  the  body. 

In  this  chapter  the  leading  characters  and  chief  modifications  of  the 


THE    STBUCTUBE    OF    THE    KI.KMK.NTAKV    TISSUES.  19 

first  two  of  the  great  groups  of  tissues — the  Epithelial  and  Connective — 
will  be  described;  while  the  others  will  be  appropriately  considered  in 
the  chapters  treating  of  their  physiology. 

Epithelium. 

The  term  epithelium  is  applied  to  the  cells  covering  the  skin,  the 
mucous  and  serous  membranes,  and  to  those  forming  a  lining  to  other 
parts  of  the  body  as  well  as  entering  into  the  formation  of  glands.  For 
example: — 

Epithelium  clothes  (1)  the  exterior  surface  of  the  body,  forming  the 
epidermis  Avith  its  appendages — nails  and  hairs;  becoming  continuous  at 
the  chief  orifices  of  the  body — nose,  mouth,  anus,  and  urethra — with  the 
(2)  epithelium  which  lines  the  whole  length  of  the  (3)  respiratory,  ali- 
mentary and  genito-urinary  tracts,  together  with  the  ducts  of  their 
various  glands.  Epithelium  also  lines  the  cavities  of  (4)  the  brain,  and 
the  central  canal  of  the  spinal  cord,  (5)  the  serous  and  synovial  mem- 
branes, and  (6)  the  interior  of  all  blood-vessels  and  lymphatics. 

Epithelial  cells  possess  an  intracellular  and  an  intranuclear  network 
(p.  17).  They  are  held  together  by  a  clear,  albuminous,  cement  sub- 
stance. The  viscid  semi-fluid  consistency,  both  of  cells  and  intercellular 
substance,  permits  such  changes  of  shape  and  arrangement  in  the  indi- 
vidual cells  as  are  necessary  if  the  epithelium  is  to  maintain  its  integrity 
in  organs  the  area  of  whose  free  surface  is  so  constantly  changing,  as  the 
stomach,  lungs,  etc.  Thus,  if  there  be  but  a  single  layer  of  cells,  as  in 
the  epithelium  lining  the  air  vesicles  of  the  lungs,  the  stretching  of  this 
membrane  causes  such  a  thinning  out  of  the.  cells  that  they  change  their 
shape  from  spheroidal  or  short  columnar,  to  squamous,  and  vice  versa, 
when  the  membrane  shrinks. 

Epithelial  tissues  are  non-vascular,  but  in  some  varieties  minute 
channels  exist  between  the  cells  of  certain  layers  through  which  they 
may  be  supplied  with  nourishment  from  the  subjacent  blood-vessels. 
^Nerve  fibres  are  supplied  to  the  cells  of  many  epithelia. 

Epithelial  tissue  is  classified  according  as  the  cells  composing  it  are 
arranged  in  a  single  layer  when  it  is  simple,  or  in  several  layers  when  it 
is  called  stratified  or  laminated,  or  in  two  or  three  layers  occupying  a 
position  between  the  other  two  forms,  when  it  is  termed  transitional. 
Of  each  form,  when  there  are  several  varieties,  they  are  named  according 
to  the  shape  of  the  cells  composing  it. 

A.  Simple. — (1.)  Squamous,  scaly,  pavement  or  tesselated; 

(2.)  Spheroidal  or  glandular; 

(3.)  Columnar,  cylindrical,  conical  or  goblet-shaped; 

(4.)  Ciliated. 

B.  Transitional. 


20 


HANDBOOK    OF    PHYSIOLOGY. 


C.   Stratified. 

A.  Simple. — Squamous  Epithelium  (Fig.  13). — Arranged  as  a  single 
layer,  this  form  of  epithelium  is  found  as  (a)  the  pigmentary  layer  of 
the  retina,  and  forms  the  lining  of  (b)  the  interior  of  the  serous  and 
and  synovial  sacs,  (c)  the  alveoli  of  the  lungs,  and  (d)  of  the  heart,  blood  - 
and  lymph-vessels.  It  consists  of  cells,  which  are  flattened  and  scaly, 
with  a  more  or  less  irregular  outline. 


Fig.  13. — Squamous  epithelium  scales  from 
the  inside  of  the  mouth.     X  260.     (Henle.) 


Fig.  14.— Pigment  cells  from  the  retina.  Ar 
cells  still  cohering,  seen  on  their  surface ;  ar 
nucleus  indistinctly  seen.  In  the  other  cells 
the  nucleus  is  concealed  by  the  pigment  gra- 
nules. B,  two  cells  seen  in  profile  ;  a,  the 
outer  or  posterior  part  containing  scarcely 
any  pigment,    x   370.    (Henle.) 


In  the  pigment  cells  of  the  retina,  there  is  a  deposit  of  pigment  in 
the  cell-substance.  This  pigment  consists  of  minute  molecules  of  mela- 
nin, imbedded  in  the  cell-substance  and  almost  concealing  the  nucleus, 
which  is  itself  transparent  (Fig.  14). 

In  white  rabbits  and  other  albino  animals,  in  which  the  pigment  of 
the  eye  is  absent,  this  layer  is  found  to  consist  of  colorless  pavement 
epithelial  cells. 

The  squamous  epithelium  which  is  found  as  a  single  layer  lining  the 
alveoli  of  the  lungs,  the  serous  membranes,  and  the  interior  of  blood- 
and  lymphatic-vessels,  is  generally  called  by  a  distinct  name — Endo- 
thelium. 

The  presence  of  endothelium  may  bo  demonstrated  by  staining  the 
part  lined  by  it  with  silver  nitrate. 

When  a  small  portion  of  a  perfectly  fresh  serous  membrane  for  ex- 
ample, as.  the  mesentery  or  omentum  (Fig.  15),  is  immersed  for  a  few 
minutes  in  a  quarter  per  cent  solution  of  silver  nitrate,  washed  with 
distilled  water  and  exposed  to  the  action  of  light,  the  silver  oxide  is 
precipitated  in  the  intercellular  cement  substance  and  the  endothelial 
cells  are  thus  mapped  out  by  fine  dark  and  generally  sinous  lines  of  ex- 
treme delicacy.  The  cells  vary  in  size  and  shape,  and  are  as  a  rule 
irregular  in  outline;  those  lining  the  interior  of  blood-vessels  and  lym- 
phatics being  spindle-shape  with  a  very  wavy  outlineo  They  inclose  a 
clear,  oval  nucleus,  which,  when  the  cell  is  viewed  in  profile,  is  seen  to 
project  from  its  surface.  The  nuclei  are  not  however  evident  unless  the 
tissue  which  has  been  already  stained  in  silver  nitrate,  is  placed  in  an- 


THE    STBUCTUBE    01?    THE    KI.KMK.NTAIiV     1I»I  Efl. 


21 


other  dye,  such  as  hematoxylin;  which  has  the  property  of  picking  out 

its  nuclei. 

Endothelial  cells   may  be  ciliated,  e.  g.,   those  in  the    mesentery  of 
frogs,  especially  about  the  breeding  season. 


Fig.  15.— Part  of  the  omentum  of  a  cat,  stained  in  silver  nitrate,  x  100.  The  tissue  forms  a 
"fenestrated  membrane  "  that  is  to  say,  one  which  is  studded  with  holes  or  windows.  In  the  figure 
these  are  of  various  shapes  and  sizes,  leaving  trabecules,  the  basis  of  which  is  fibrous  tissue.  The 
trabeculse  are  of  various  sizes,  and  are  covered  with  endothelial  cells,  the  nuclei  of  which  have  been 
made  evident  by  staining;  with  hsematoxyliu  after  the  silver  nitrate  has  outlined  the  cells  by  stain- 
ing the  intercellular  substance.    (V.  D.  Harris.) 

Besides  the  ordinary  endothelial  cells  above   described,  there  are 
found  on  the  omentum  and  parts  of  the  pleura  of  many  animals,  little 


Fig.  16.  —Abdominal  surface  of  centrum  tendineum  of  diaphragm  of  rabbit,  showing  the  gen- 
eral polygonal  shape  of  the  endothelial  cells  :  each  is  nucleated.    (Klein.)    x  300. 

bud-like  processes  or  nodules,  consisting  of  small  polyhedral  granular 
cells,  rounded  on  their  free  surface,  which  multiply  very  rapidly  by 
division  (Fig.  17).  These  constitute  what  is  known  as  "germinating 
endothelium."  The  process  of  germination  doubtless  goes  on  in  health, 
and  the  small  cells  which  are  thrown  off  in  succession  are  carried  into 
the  lymphatics,  and  contribute  to  the  number  of  the  Lymph  corpuscles. 


22 


HANDBOOK    OF    PHYSIOLOGY. 


The  buds  may  be  enormously  increased  both  in  number  and  size  in  cer- 
tain diseased  conditions. 

On  those  portions  of  the  peritoneum  and  other  serous  membranes  in 


Fig.  17.— Silver-stained  preparation  of  great  omentum  of  dog,  which  shows,  amongst  the  flat 
endothelium  of  the  surface,  small  and  large  groups  of  germinating  endothelium  between  which 
numbers  of  stomata  are  to  be  seen.    (Klein.)     X  3U0. 

which  lymphatics  abound  (Fig.  18),  apertures  are  found  surrounded  by 
small  more  or  less  cubical  cells.     These  apertures  are  called  stomata. 


Fig.  18.— Peritoneal  surface  of  septum  cisternse  lymphaticse  magnse  of  frog.  The  stomata, 
some  of  which  are  open,  some  collapsed,  are  surrounded  by  germinating  endothelium.  uuein.> 
X  160. 

They  are  particularly  well  seen  in  the  anterior  wall  of  the  great  lymph 
sac  of  the  frog  (Fig.  18),  and  in  the  omentum  of  the  rabbit.  These  are 
really  the  open  mouths  of  lymphatic  vessels  or  spaces,  and  through  them 
lymph-corpuscles,  and  the  serous  fluid  from  the  serous  cavity,  pass  int& 


THE    STRUCTURE    OF    THE    KLEMENTARY    TISSUES. 


23 


the  lymphatic  system.  They  should  be  distinguished  from  smaller  and 
more  numerous  apertures  between  the  cells  which  are  not  lined  by  small 
cells,  although  the  surrounding  cells  seem  to  radiate  from  them,  filled 
up  by  intercellular  substance  or  by  processes  of  the  cells  underneath. 
These  are  called  pseudo-stomata  (Fig.  16). 

In  the  neighborhood  of  the  stomata,  the  cells  often  manifest  indica- 
tions of  germinating.  They  may  be  either  large  with  two  or  more  nu- 
clei, or  about  half  the  size  of  the  generality  of  cells.  Germinating  cells 
of  this  kind  or  of  the  kind  above  described,  are  generally  very  granular. 

2.  Spheroidal  epithelial  cells  are  the  active  secreting  agents  in  most 
secreting  glands,  and  hence  are  often  termed  glandular  ;  they  are  gene- 
rally more  or  less  rounded  in  outline  :  often  polygonal  from  mutual 
pressure. 

Excellent  examples  are  to  be  found  in  the  liver,  in  the  secreting  tubes 
of  the  kidney,  and  in  the  salivary  and  gastric  glands  (Fig.  19). 


Fig.  19.— Glandular  epithelium.    A,  small  lobule  of  a  mucous  gland  of  the  tongue,  showing 
nucleated  glandular  spheroidal  cells.    B,  Liver  cells.     X  200.    (V.  D.  Harris.) 


3.  Columnar  epithelium  (Fig.  21,  a  and  b)  as  a  single  layer,  lines 
(a.)  the  mucous  membrane  of  the  stomach  and  intestines,  from  the  car- 
diac orifice  of  the  stomach  to  the  anus,  and  (b.)  wholly  or  in  part  the 
ducts  of  the  glands  opening  on  its  free  surface  ;  also  (c.)  many  gland- 
ducts  in  other  regions  of  the  body,  e.  (/.,  mammary,  salivary,  etc. 

Columnar  epithelium  consists  of  cells  which  are  cylindrical  or  pris- 
matic in  form,  and  contain  a  large  oval  nucleus.  They  vary  in  size  and 
also  in  shape  to  a  certain  extent,  the  outline  being  often  irregular  from 
pressure  of  neighboring  cells,  but  speaking  generally  one  end  of  the  cell 
is  narrower  than  the  other,  and  by  this  end  the  cell  is  attached  to  the 
membrane  beneath.  The  intercellular  and  internuclear  network  are 
well  developed. 

The  columnar  epithelial  cells  of  the  alimentary  canal  possess  a  struc- 
tureless layer  on   their  free   surface  :  such   a   layer,   appearing  striated 


M 


HANDBOOK    OF    PHYSIOLOGY 


when  viewed  in  section,  is  termed  the  "striated  basilar   border"  (Fig 
20,  a,  a). 


Fig.  20.— A.  Vertical  section  of  a  villus  of  the  small  intestine  of  a  cat.  a.  Striated  basilar  bor- 
der of  the  epithelium,  b.  Columnar  epithelium,  c.  Goblet  cells,  d.  Central  lymph-vessel  e. 
Smooth  muscular  fibres.  /.  Adenoid  stroma  of  the  villus  in  which  lymph  corpuscles  lie.  B.  Goblet- 
cells.    (Klein.) 


Columnar   cells  may  undergo  a  curious  transformation,  and  from 
the  alteration  in  their  shape  are  termed   "goblet-cells"  (Fig.  20,  A,  c, 


i_  J 


Fig.  21.— Columnar  epithelial  cells  from 
the  intestinal  mucous  menbrane  of  a  cat.— a 
and  b,  small  cells  of  the  lower  layer  ;  c, 
superficial  layer  ;  d,  goblet  cells.    (Cadiat.) 


Fig.  22.— Columnar  ciliated  cells  from  the 
human  nasal  membrane :  magnified  300 
diameters.    (Sharpey.) 


and  b).     These  are  hardly  ever  seen  in  a  perfectly  fresh  specimen:  but 
if  such  a   specimen   be  watched  for  some  time,   little  knobs  are  seen 


Fig.  23.-A.  Spheroidal  ciliated  cells  from  the  mouth  of  the  frog.  X  300  diameters.  (Sharpey.) 
B.  a.  Ciliated  columnar  epithelium  lining  a  bronchus,  b.  Branched  conuective-tissue  corpuscles. 
(Klein  and  Noble  Smith.) 

gradually  appearing  on  the  free  surface  of  the  epithelium,  and  are  finally 
detached;  these  consist  of  the  cell-contents  which  are  discharged  by  the 


TIIK    STRUCTURE    <>!•'    THE    Kl.KM  EN  TAB  V    TISSUES.  25 

•open  mouth  of  the  globet,  leaving  tin;  nucleus  surroanded  by  the  re- 
mains of  the  protoplasm  in  its  narrow  stem. 

This  transformation  is  a  normal  process  which  is  continually  going 
on  during  life,  the  discharged  cell-contents  contributing  to  form  mucus, 
the  cells  being  supposed  in  many  cases  to  recover  their  original  shape. 
It  is  an  example  of  secretion. 

4.  Ciliated  cells  are  generally  cylindrical  (Fig.  23,  b),  but  may  be 
spheroidal  or  even  almost  squamous  in  shape  (Fig.  23,  a). 

This  form  of  epithelium  lines — (a.)  the  whole  of  the  respiratory 
tract  from  the  larynx,  except  over  the  vocal  cords,  to  the  finest  sub- 
divisions of  the  bronchi,  also  the  lower  parts  of  the  nasal  passages,  the 
nasal  duct,  and  the  lachrymal  sac.  In  part  of  this  tract,  however, 
the  epithelium  is  in  several  layers,  of  which  only  the  most  superficial 
is  ciliated,  so  that  it  should  more  accurately  be  termed  transitional 
(p.  26)  or  stratified,  (b.),  some  portions  of  the  generative  apparatus 
in  the  male,  viz.,  lining  the  "  vasa  efferentia''  of  the  testicle,  and  their 
prolongations  as  far  as  the  lower  end  of  the  epididymis;  in  the  female 
(c.)  commencing  about  the  middle  of  the  neck  of  the  uterus,  and  ex- 
tending throughout  the  uterus  and  Fallopian  tubes  to  their  fimbriated 
extremities,  and  even  for  a  short  distance  on  the  peritoneal  surface  of 
the  latter,  (d.)  The  ventricles  of  the  brain  and  the  central  canal  of 
the  spinal  cord  are  clothed  with  ciliated  epithelium  in  the  child,  but  in 
the  adult  this  epithelium  is  limited  to  the  central  canal  of  the  cord. 

The  Cilia,  or  fine  hair-like  processes  which  give  the  name  to  this 
variety  of  epithelium,  vary  a  good  deal  in  size  in  different  classes  of  ani- 
mals, being  very  much  smaller  in  the  higher  than  among  the  lower 
orders,  in  which  they  sometimes  exceed  in  length  the  cell  itself. 

The  number  of  cilia  on  any  one  cell  ranges  from  ten  to  thirty,  and 
those  attached  to  the  same  cell  are  often  of  different  lengths.  When 
living  ciliated  epithelium,  e.  y.,  from  the  gill  of '  a  mussel,  or  oyster,  or 
from  the  mouth  of  the  frog,  or  from  a  scraping  from  a  polypus  from 
the  human  nose,  is  examined  Tinder  the  microscope,  the  cilia  are  seen  to 
be  in  constant  rapid  motion;  each  cilium  being  fixed  at  one  end,  and 
swinging  or  lashing  to  and  fro.  The  general  impression  given  to  the 
eye  of  the  observer  is  very  similar  to  that  produced  by  waves  in  a  field 
of  corn,  or  swifty  running  and  rippling  water,  and  the  result  of  their 
movement  is  to  produce  a  continuous  current  in  a  definite  direction, 
arid  this  direction  is  invariably  the  same  on  the  same  surface,  being 
always,  in  the  case  of  a  cavity,  towards  its  external  orifice. 

Ciliary  Motion. — Ciliary,  which  is  closely  allied  to  amoeboid  and 
muscular  motion,  is  alike  independent  of  the  will,  of  the  direct  influence 
of  the  nervous  system,  and  of  muscular  contraction.  It  continues  for 
several  hours  after  death  or  removal  from  the  body,  provided  the  portion 
of  tissue  under  examination  lie  kepi  moist.  Its  independence  of  thener- 


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HANDBOOK    OF    PHYSIOLOGY. 


vous  system  is  shown  also  in  its  occurrence  in  the  lowest  invertebrate 
animals  apparently  unprovided  with  anything  analogous  to  a  nervous 
system,  in  its  persistence  in  animals  killed  by  prussic  acid,  by  narcotic 
or  other  poisons,  and  after  the  direct  application  of  narcotics,  such  as 
morphia,  opium,  and  belladonna,  to  the  ciliary  surface,  or  of  electricity 
through  it.  The  vapor  of  chloroform  arrests  the  motion;  but  it  is  re- 
newed on  the  discontinuance  of  the  application  (Lister).  The  movement 
ceases  when  the  cilia  are  deprived  of  oxygen,  but  is  revived  on  the 
admission  of  this  gas.  Carbonic  acid  stops  the  movement.  The  contact 
of  various  substances,  e.g.,  bile,  strong  acids,  and  alkalies,  will  stop  the 


Fig.  24.—  Epithelium  of  the  bladder,  a, 
one  of  the  cells  of  the  first  row  ;  b,  a  cell  of 
the  second  row ;  c,  cells  in  situ,  of  first, 
second,  and  deepest  layers,    f Obersteiner.) 


Fig.  25.— Transitional  epithelial  cells  from 
a  scraping  of  the  mucous  membrane  of  the 
bladder  of  the  rabbit.     (V.  D.  Harris."! 


motion  altogether;  but  this  seems  to  depend  chiefly  on  destruction  of 
the  delicate  substance  of  which  the  cilia  are  composed.  Temperatures 
above  45°  C,  and  below  0°  C,  stop  the  movement;  but  moderate  heat 
and  dilute  alkalies  are  favorable  to  the  action  and  revive  the  movement 
after  temporary  cessation. 

As  a  special  subdivision  of  ciliary  action  may  be  mentioned  the  mo- 
tion of  spermatozoa,  which  may  be  regarded  as  cells  with  a  single  cil- 
ium. 

B.  Transitional  Epithelium. — This  term  has  been  applied  to  cells, 
which  are  neither  arranged  in  a  single  layer,  as  is  the  case  with  simple 
epithelium,  nor  yet  in  many  superimposed  strata  as  in  laminated ;  in 
other  words,  it  is  employed  when  epithelial  cells  are  found  in  two,  three, 
or  four  superimposed  layers. 

The  upper  layer  may  be  either  columuar,  ciliated,  or  squamous. 
When  the  upper  layer  is  columnar  or  ciliated,  the  second  layer  consists 
of  smaller  cells  fitted  into  the  inequalities  of  the  cells  above  them,  as  in 
the  trachea  (Fig.  24,  b). 

The  epithelium  which  is  met  with  lining  the  urinary  bladder  and 
ureters  is,  however,  the  transitional  par  excellence.  In  this  variety  there 
are  two  or  three  layers  of  cells,  the  upper  being  more  or  less  flattened 
according  to  the  full  or  collapsed  condition  of  the  organ,  their  under 


THE    ST  KIT  TIKE    OI-'    THK    ELEMENTARY    TISSUES. 


% 


surface  being  marked  with  one  or  more  depressions,  into  which  the  heads 
of  the  next  layer  of  club-shaped  cells  fit.  Between  the  lower  and  nar- 
rower parts  of  the  second  row  of  cells,  are  fixed  the  irregular  cells  which 
constitute  the  third  row,  and  in  like  manner  sometimes  a  fourth  row 
(Fig.  24).  It  can  he  easily  understood,  therefore,  that  if  a  scraping  of 
the  mucous  membrane  of  the  bladder  be  teased,  and  examined  under  the 
microscope,  cells  of  a  great  variety  of  forms  may  be  made  out  (Fig.  25). 
Each  cell  contains  ;i  large  nucleus,  and  the  larger  and  superficial  cells 
often  possess  two. 

C.  Stratified  Epithelium. — This  term  is  employed  when  the  cells 
forming  the  epithelium  are  arranged  in  a  considerable  number  of  super- 
imposed layers.  The  shape  and  size  of  the  cells  of  the  different  layers, 
as  well  as  the  number  of  the  layers,  vary  in  different  situations.  Thus 
the  superficial  cells  are  as  a  rule  of  the  squamous,  or  scaly  variety,  and 
the  deepest  of  the  columnar  form. 

The  cells  of  the  intermediate  layers  are  of  different  shapes,  but  those 
of  the  middle  layers  are  more  or  less  rounded.  The  superficial  cells  over- 
lap by  their  edges  (Fig.  26);  they  are  broad  (Fig.  13).  Their  chemical 
composition  is  different  from  that  of  the  underlying  cells,  as  they  con- 
tain keratin,  and  are  therefore  horny  in  character. 

The  nucleus  is  often  not  apparent.  The  really  cellular  nature  of 
even  the  dry  and  shrivelled  scales  cast  off  from  the  surface  of  the  epi- 
dermis, can  be  proved  by  the  application  of  caustic  potash,  which  causes 
them  rapidly  to  swell  and  assume  their  original  form. 

The  squamous  cells  exist  in  the  greatest  number  of  layers  in  the  epi- 
dermis or  superficial  part  of  the  skin;  and  the  most  superficial  of  these 


Fig.  26.— Vertical  section  of  the  stratified  epithelium  of  the  Rabbit's  cornea,  a.  Anterior  epi- 
thelium, showing  the  different  shapes  of  the  cells  at  various  depths  from  the  free  surface.  6.  Por- 
tion of  the  substance  of  cornea.    CKleiu.  I 

are  being  continually  removed  by  friction,  and  new  cells  from  below  sup- 
ply the  place  of  those  cast  off. 

The  intermediate  cells  approach  more  to  the  flat  variety  the  nearer 
they  are  to  the  surface,  and  to  the  columnar  as  they  approach  the  lowest 
layer.  There  may  be  considerable  intercellular  intervals;  and  in  many 
of  the  deeper  layers  of  epithelium  in  the  mouth  and  skin,  the  outline  of 


:>S 


HANDBOOK    OF    PHYSIOLOGY. 


Fig.  27.— Jagged  cells  of  the  middle 
layers  of  pavement  epithelium,  from  a 
vertical  section  of  the  gum  of  a  new- 
born infant.    ( Klein. ) 


the  cells  is  very  irregular,  in  consequence  of  processes  passing  from  cell 
to  cell  across  these  intervals. 

Such  cells  (Fig.  27)  are  termed  "  ridge 
and  furrow/'  "cogged"  or  "prickle" 
cells.  These  "prickles"  are  prolonga- 
tions of  the  intra-cellular  network  which 
run  across  from  cell  to  cell,  thus  joining 
them  together  (Martyn),  the  interstices 
being  filled  by  the  transparent  intercel- 
lular cement  substance.  When  this  in- 
creases in  quantity  in  inflammation,  the 
cells  are  pushed  further  apart,  and  the 
connecting  fibrils  or  '''prickles"  elon- 
gated, and  therefore  more  clearly  visible. 
The  columnar  cells  of  the  deepest  layer  are  distinctly  nucleated;  they 
multiply  rapidly  by  division;  and  as  new  cells  are  formed  beneath,  they 
press  the  older  cells  forwards  to  be  in  turn  pressed  forwards  themselves 
towards  the  surface,  gradually  altering  in  shape  and  chemical  composi- 
tion until  they  are  cast  off  from  the  surface. 

Stratified  epithelium  is  found  in  the  following  situations: — (1.) 
Forming  the  epidermis,  covering  the  whole  of  the  external  surface  df 
the  body;  (2.)  Covering  the  mucous  membrane  of  the  tongue,  mouth, 
pharynx,  and  oesophagus;  (3.)  As  the  conjunctival  epithelium,  covering 
the  cornea;  (4.)  Lining  the  vaginal  part  of  the  cervix  uteri. 

Functions  of  Epithelium. — According  to  function,  epithelial  cells 
may  be  classified  as: — (1.)  Protective,  e.g.,  in  the  skin,  mouth,  blood- 
vessels, etc.  (2.)  Protective  and  moving — ciliated  epithelium.  (3.) 
Secreting — glandular  epithelium;  or,  Secreting  formed  elements — epi- 
thelium of  testicle  secreting  spermatozoa.  (4.)  Protective  and  secreting, 
e.g.,  epithelium  of  intestine.  (5.)  Sensorial,  e.g.,  olfactory  cells,  rods 
and  cones  of  retina,  organ  of  Corti. 

Epithelium  forms  a  continuous  smooth  investment  over  the  whole 
body,  being  thickened  into  a  hard,  horny  tissue  at  the  points  most  ex- 
posed to  pressure,  and  developing  various  appendages,  such  as  hairs  and 
nails,  whose  structure  and  functions  will  be  considered  in  a  future  chap- 
ter. Epithelium  lines  also  the  sensorial  surfaces  of  the  eye,  ear,  nose, 
and  mouth,  and  thus  serves  as  the  medium  through  which  all  impressions 
from  the  external  world — touch,  smell,  taste,  sight,  hearing — reach  the 
delicate  nerve-endings,  whence  they  are  conveyed  to  the  brain. 

The  ciliated  epithelium  which  lines  the  air-passages  serves  not  only 
as  a  protective  investment,  but  also  by  the  movements  of  its  cilia 
promotes  currents  of  the  air  in  the  bronchi  and  bronchia,  and  is  enabled 
to  propel  fluids  and  minute  particles  of  solid  matter  so  as  to  aid  their 
expulsion  from  the  body.  In  the  case  of  the  Fallopian  tube,  this  agency 
assists  the  progress  of  the  ovum  towards  the  cavity  of  the  "uterus.  Of 
the  purposes  served  by  cilia  in  the  ventricles  of  the  brain  nothing  is 
known. 


t'HB    STRUCTUBE    OF    THE    EI.EMEXTAKY     U88UEB. 


29 


The  epithelium  of  the  various  glands,  and  of  the  whole  intestinal 
tract,  has  the  power  of  secretion,  i.e.,  of  chemically  transforming  certain 
materials  of  the  blood;  in  the  case  of  mucus  and  saliva  this  has  been 
proved  to  involve  the  transformation  of  the  epithelial  cells  themselves; 
the  cell-substance  of  the  epithelial  cells  of  the  intestine  being  discharged 
by  the  rupture  of  their  envelopes,  as  mucus. 

Epithelium  is  likewise  concerned  in  the  processes  of  transudation, 
diffusion,  and  absorption. 

It  is  constantly  being  shed  at  the  free  surface,  and  reproduced  in  the 
deeper  layers.  The  various  stages  of  its  growth  and  development  can 
be  well  seen  in  a  section  of  any  laminated  epithelium  such  as  the  epi- 
dermis. 

The  Connective  Tissues. 

This  group  of  tissues  forms  the  Skeleton  with  its  various  connections 
— bones,  cartilages,  and  ligaments — and  also  affords  a  supporting  frame- 
work and  investment  to  the  various  organs  composed  of  nervous,  muscu- 
lar, and  glandular  tissue.     Its  chief  function  is  the  mechanical  one  of 


Fig.  28.— Horizontal  preparation  of  cornea  of  frog,  stained  in  gold  chloride  ;  showing  the  net- 
work of  branched  cornea  corpuscles.  The  ground  substance  is  completely  colorless,  x  400. 
(Klein. ) 

support,  and  for  this  purpose  it  is  so  intimately  interwoven  with  nearly 
all  the  textures  of  the  body,  that  if  all  other  tissues  could  be  removed, 
and  the  connective  tissues  left,  we  should  have  a  wonderfully  exact 
model  of  almost  every  organ  and  tissue  in  the  body,  correct  even  to  the 
smallest  minutiae  of  structure. 

Classification  of  Connective  Tissues. — The  chief  varieties  of  con- 
nective tissues  may  be  thus  classified  : — 

I.  The  Fibrous  Connective  Tissues. 
A. — Chief  Forms. 

a.  White  fibrous. 

b.  Elastic. 

c.  Areolar. 


30 


HANDBOOK    OF   PHYSIOLOGY. 


B. — Special  Varieties. 

a.  Gelatinous. 

b.  Adenoid  or  Retiform. 

c.  Neuroglia. 

d.  Adipose. 

II.  Cartilage. 
III.  Bone. 

Structure  of  Connective  Tissues. 
All  of  the  varieties  of  connective  tissue  are  made  up  of  two  elements, 
namely,  cells  and  intercellular  substance. 
(A.)  Cells. — The  cells  are  of  two  kinds. 

(a.)  Fixed. — These  are  cells  of  a  flattened  shape,  with  branched  pro- 
cesses, which  are  often  united  together  to  form  a  network  :  they  can  be 
most  readily  observed  in  the  cornea,  in  which  they  are  arranged,  layer 

above  layer,  parallel  to  the  free  surface. 
They  lie  in  spaces,  in  the  intercellular  or 
ground  substance,  which  are  of  the  same 
shape  as  the  cells  they  contain,  but  rather 
larger,  and  which  form  by  anastomosis  a  sys- 
tem of  branching  canals  freely  communicat- 
ing (Fig.  28). 

To  this  class  of  cells  belong  the  flattened 
tendon  corpuscles  which  are  arranged  in 
long  lines  or  rows  parallel  to  the  fibres  (Fig. 
34). 

These  branched  cells,  in  certain  situa- 
tions, contain  a  number  of  pigment-grannies, 
giving  them  a  dark  appearance  :  they  form 
one  variety  of  pigment-cell.  Branched  pigment-cells  of  this  kind  are  found 
in  the  outer  layers  of  the  choroid  (Fig.  29) .  In  many  of  the  lower  animals, 
such  as  the  frog,  they  are  found  widely  distributed,  uot  only  in  the  skin, 
but  also  in  internal  parts,  e.  g.,  the  mesentery  and  sheaths  of  blood-ves- 
sels. In  the  web  of  the  frog's  foot  such  cells  may  be  seen,  with  pigment- 
granules  evenly  distributed  throughout  the  body  of  the  cell,  and  its 
processes  ;  but  under  the  action  of  light,  electricity,  and  other  stimuli, 
the  pigment-granules  become  massed  in  the  body  of  the  cell,  leaving  the 
processes  quite  hyaline  ;  if  the  stimulus  be  removed,  they  will  gradually 
be  distributed  again  throughout  the  processes.  Thus  the  skin  in  the 
frog  is  sometimes  uniformly  dusky,  and  sometimes  quite  light-colored, 
with  isolated  dark  spots.  In  the  choroid  anb  retina  the  pigment-cells 
absorb  light. 

(b.)  Amoeboid  cells,  of  an  approximately  spherical  shape:  they  have  a 
great  general  resemblance  to  colorless  blood-corpuscles  (Fig.   2),  with 


Fig.  29.— Ramified  pigment- 
■cells,  from  the  tissue  of  the  choroid 
coat  of  the  eye.  x  350.  a,  cell  with 
pigment ;  6,  colorless  fusiform 
cells.    (Kolliker.) 


THE    8TJBU0TTTBE    OF    THE    ELEMENTABY    TISSUES. 


31 


HfW  "^^ 


which  some  of  them  are  probably  identical.  They  consist  of  finely 
granular  nucleated  protoplasm,  and  have  the  property,  not  only  of 
changing  their  form,  but  also  moving  about,  whence  they  are  termed 
migratory.  They  are  readily  distinguished  from  the  branched  connec- 
tive-tissue corpuscles  by  their  free  condition,  and  the  absence  of  pro- 
cesses. Some  are  much  larger  than  others,  and  are  found  especially  in 
the  sublingual  gland  of  the  dog  and  guinea  pig,  and  in  the  mucous 
membrane  of  the  intestine.  A  second  variety  of  these  cells  called  plas- 
ma cells  (Waldeyer)  are  larger  than  the  amoeboid  cells,  apparently 
granular,  less  active  in  their  movements.  They  are  chiefly  to  be  found 
in  the  intermuscular  septa,  in  the 
mucous  and  submucous  coats  of 
the  intestine,  in  lymphatic  glands, 
and  in  the  omentum. 

(B.)  Intercellular  substance. 
— This  may  be  fibrillar,  as  in  the 
fibrous  tissues,  and  in  certain  varie- 
ties of  cartilage  ;  or  homogeneous, 
as  in  hyaline  cartilage. 

The  fibres  composing  the  former 
are  of  two  kinds — (a.)  White  fibres. 
(b.)  Yellow  elastic  fibres. 

(«.)  White  Fibres. — These  are 
arranged  parallel  to  each  other  in 
wavy  bundles  of  various  sizes  :  such 
bundles  may  either  have  a  parallel 
arrangement  (Fig.  31),  or  may  pro- 
duce quite  a  felted  texture  by  their 

interlacement.  The  individual  fibres  composing  these  fasciculi  are 
homogeneous,  unbranched,  and  of  the  same  diameter  throughout.  They 
can  readily  be  isolated  by  macerating  a  portion  of  white  fibrous  tissue 
(e.  g.,  a  small  piece  of  tendon)  for  a  short  time  in  lime,  or  baryta-water, 
or  in  a  solution  of  common  salt,  or  of  potassium  permanganate  :  these 
reagents  possess  the  power  of  dissolving  the  cementing  interfibrillar  sub- 
stance (which  is  nearly  allied  to  syntonin),  and  of  thus  separating  the 
fibres  from  each  other.     By  prolonged  boiling  the  fibres  yield  gelatin. 

{b.)  Yellow  Elastic  Fibres  (Fig.  32)  are  of  all  sizes,  from  excessively 
fine  fibrils  up  to  fibres  of  considerable  thickness  :  they  are  distinguished 
from  white  fibres  by  the  following  characters  : — (I.)  Their  great  power 
of  resistance  even  to  the  prolonged  action  of  chemical  reagents,  e.g., 
Caustic  Soda,  Acetic  Acid,  etc.  (2.)  Their  well-defined  outlines.  (3.) 
Their  great  tendency  to  branch  and  form  networks  by  anastomosis. 
(4.)  They  very  often  have   a   twisted   corkscrew-like  appearance,    and 


Fig.  30.— Flat,  pigmented,  branched  con- 
ective-tissue  cells  from  the  sheath  of  a  large 
blood-vessel  of  frog's  mesentery  ;  the  pigment 
is  not  distributed  uniformly  through  the 
substance  of  the  larger  cell,  consequently 
some  parts  of  the  cell  look  blacker  than  others 
(uncontracted  state).  In  the  two  smaller 
cells  most  of  the  pigment,  is  withdrawn  into 
the  cell-body,  so  that  they  appear  smaller 
blacker,  and  less  branched.  X  350.  (Klein  and 
Noble  Smith.) 


3? 


HANDBOOK    OF    PHYSIOLOGY. 


their  fiee  ends  usually  curl  up.    (5.)  They  are  of  a  yellowish  tint,  and 
very  elastic. 


mm 
■  mi 

fWii'Wfflllf 


Fig.  31.—  Fibrous  tissue  of  cornea,  showing 
bundles  of  fibres  with  a  few  scattered  fusi- 
form cells  lying  in  the  inter-fasicular  spaces. 
X  400.    (Klein  and  Noble  Smith.) 


Fig.  32.— Elastic  fibres  from  the  ligamenta 
subflava.    x  aOO.    (Sharpey.) 


These  fibres  yield  a  gelatinous  substance  called  elastin. 


Varieties    of    Connective    Tissue. 

I.  Fibrous  Connective  Tissues. 

A. — Chief  Forms. — (a.)  White  Fibrous  Tissue. 

Distribution. — Typically  in  tendon;  in  ligaments,  in  the  periosteum 
and  perichondrium,  the  dura  mater,  the  pericardium,  the  sclerotic  coat 
of  the  eye,  the  fibrous  sheath  of  the  testicle;  in  the  fascia?  and  aponeurosis 
of  muscles,  and  in  the  sheaths  of  lymphatic  glands. 

Structure. — To  the  naked  eye,  tendons,  and  many  of  the  fibrous 
membranes,  when  in  a  fresh  state,  present  an  appearance  as  of  watered 
silk.  This  is  due  to  the  arrangement  of  the  fibres  in  wavy  parallel 
bundles.  Under  the  microscope,  the  tissue  appears  to  consist  of  long, 
often  parallel,  bundles  of  fibres  of  different  sizes.  The  fibres  of  the 
same  bundle  now  and  then  intersect  each  other.  The  cells  in  tendons 
(Fig.  34)  are  arranged  in  long  chains  in  the  ground  substance  separating 
the  bundles  of  fibres,  and  are  more  or  less  regularly  quadrilateral  with 
large  round  nuclei  containing  nucleoli,  which  are  generally  placed  so  as 
to  be  contiguous  in  two  cells.  The  cells  consist  of  a  body,  which  is 
thick,  from  which  processes  pass  in  various  directions  into,  and  partially 
filling  up  the  spaces  between  the  bundles  of  fibres.  The  rows  of  cells 
are  separated  from  one  another  by  lines  of  cement  substance.  The  cell 
spaces  can  be  brought  into  view  by  silver  nitrate.     The  cells  are  gene- 


THE    STRUCTURE    OK    TUB    ELEMENTARY    TISSUES. 


33 


rally  marked  by  one  or  more  lines  or  stripes  when  viewed  longitudi- 
nally. This  appearance  is  really  produced  by  the  laminar  extension 
either  projecting  upwards  or  downwards. 


Fig.  33.— a.  Mature  white  fibrous  tissue  of 
tendon,  consisting  mainly  of  fibres  with  a  few 
scattered  fusiform  cells.    (Strieker.; 


Fig.  34.— Caudal  tendon  of  young  rat, 
showing  the  arrangement,  form,  and  struc- 
ture of  the  tendon  cells,     x  300.    (Klein.) 


The  branched  character  of  the  cells  is  seen  in  transverse  section  in 
Fig.  35. 

(b.)  Yellow  Elastic  Tissue. 

Distribution. — In  the  ligamentum  nuchas  of  the  ox,  horse,  and  many 
other  animals;  in  the  ligamenta  subflava  of  man;  in  the  arteries,  con- 
stituting the  fenestrated  coat  of  Henle;  in  veins;  in  the  lungs  and 
trachea;  in  the  stylo-hyoid,  thyro-hyoid,  and  crico-thyroid  ligaments;  in 
the  true  vocal  cords;  and  in  areolar  tissue. 

Structure. — Elastic  tissue  occurs  in  various  forms,  from  a  structure- 
less, elastic  membrane  to  a  tissue  whose  chief  constituents  are  bundles 
of  fibres,  crossing  each  other  at  different  angles;  when  seen  in  bundles 
elastic  fibres  are  yellowish  in  color,  but  individual  fibres  are  not  so  dis- 
tinctly colored.    The  varieties  of  the  tissue  may  be  classified  as  follows: — 

(a.)  Fine  elastic  fibrils,  which  branch  and  anastomose  to  form  a  net- 
work; this  variety  of  elastic  tissue  occurs  chiefly  in  the  skin  and  mucous 
membranes,  in  subcutaneous  and  submucous  tissue,  in  the  lungs  and 
true  vocal  cords. 

(b.)  Thick  fibres,  sometimes  cylindrical,  sometimes  flattened  like 
tape,  which  branch,  anastomose  and  form  a  network:  these  are  seen 
most  typically  in  the  ligamenta  subflava  and  also  in  the  ligamentum 
nuchas  of  such  animals  as  the  ox  and  horse,  in  which  it  is  largely  devel- 
oped (Fig.  32). 

(c.)  Elastic  membranes  with  perforations,  e.  g.,  Henle's  fenestrated 
membrane:  this  variety  is  found  chiefly  in  the  arteries  and  veins. 

(d.)  Continuous,  homogeneous  elastic  membranes,  e.  g.,  Bowman's 
3 


34 


HANDBOOK    OF   PHYSIOLOGY. 


anterior  elastic  lamina,  and  Descemet's  posterior  elastic  lamina,  both  in 
the  cornea. 

A  certain  number  of  flat  connective  tissue   cells   are  found  in  the 

ground  substance  between  the  elastic 
fibres  which  make  up  this  variety  of  con- 
nective tissue. 

(c.)  Areolar  Tissue. 
Distribution. — This  variety  has  a  very 
wide  distribution,  and  constitutes  the 
subcutaneous,  subserous  and  submucous 
tissue.  It  is  found  in  the  mucous  mem- 
branes, in  the  true  skin,  and  in  the  outer 
sheaths  of  the  blood-vessels.  It  forms 
sheaths  for  muscles,  nerves,  glands,  and 
the  internal  organs,  and,  penetrating  into 
their  interior,  supports  and  connects  the 
finest  parts. 

Structure. — To  the  naked  eye  it  ap- 
pears, when  stretched  out,  as  a  fleecy, 
white,  and  soft  meshwork  of  fine  fibrils, 
with  here  and  there  wider  films  joining  in 
it,  the  whole  tissue  being  evidently  elastic. 
The  openness  of  the  meshwork  varies  with  the  locality  from  which  the 
specimen  is  taken.  Under  the  microscope  it  is  found  to  be  made  up  of  fine 
white  fibres,  which  interlace  in  a  most  irregular  manner,  together  with 


Fig.  35. — Transverse  section  of 
tendon  from  a  cross  section  of  the  tail 
of  arabbit,  showing  sheath,  fibrous  sep- 
ta, and  branched  connective-tissue 
corpuscles.  The  spaces  left  white  in 
the  drawing  represent  the  tendinous 
fibres  in  transverse  section.  X  250. 
(Klein.) 


^ 


Fig.  36.— Magnified  view  of  the  areolar  tissue  (from  different  parts)  treated  with  acetic  acid. 
The  white  filaments  are  no  longer  seen,  and  the  yellow  or  elastic  fibres  with  the  nuclei  come  into 
view.  At  c,  elastic  fibres  wind  round  a  bundle  of  white  fibres,  which,  by  the  effect  of  the  acid,  is 
swollen  out  between  the  turns.  Some  connective-tissue  corpuscles  are  indistinctly  represented  in  c. 
(Sharpey.) 

a  variable  number  of  elastic  fibres.  On  the  addition  of  acetic  acid,  the 
white  fibres  swell  up,  and  become  gelatinous  in  appearance  (Fig.  36); 
but  as  the  elastic  fibres  resist  the  action  of  the  acid,  they  may  still  be 


J IIH    STUTCTITKK    OK    THE    ELEMENTARY    TIS8UE8. 


35 


seen  arranged  in  various  directions,  sometimes  appearing  to  pass  m  a 
more  or  less  circular  or  spiral  manner  round  a  small  gelatinous  mass  of 
changed  white  fibres.  The  cells  of  the  tissue  are  not  arranged  in  a  very 
regular  manner,  as  they  are  contained  in  the  spaces  (areolae)  between  the 
fibres.  They  communicate,  however,  with  one  another  by  branched 
processes,  and  also  with  the  cells  forming  the  walls  of  the  capillary 
blood-vessels  in  their  neighborhood.  The  fibres  are  connected  together 
with  a  certain  amount  of  albuminous  cement  substance. 

B. — Special  Forms. — (a.)  Gelatinous  Tissue. 

Distribution. — Gelatinous  connective  tissue  forms  the  chief  part  of 
the  bodies  of  jelly  fish  ;  it  is  found  in  many  parts  of  the  human  embryo, 


Fig.  37 


Fig.  38. 


Fig.  37.— Tissue  of  the  jelly  of  Wharton  from  umbilical  cord,  a,  connective-tissue  corpuscles  ; 
b,  fasciculi  of  connective  tissue;  c,  spherical  formative  cells,    i  Frey. ) 

Fig.  38.  -Part  of  a  section  of  a  lymphatic  gland,  from  which  the  corpuscles  have  been  for  the 
most  part  removed,  showing  the  adenoid  reticulum,     i  Klein  aud  Noble  Smith  I 

but  remains  in  the  adult  only  in  the  vitreous  humor  of  the  eye.  It  may 
be  best  seen  in  the  last  named  situation,  in  the  "  Whartonian  jelly "  of 
the  umbilical  cord,  and  in  the  enamel  organ  of  developing  teeth. 

Structure. — It  consists  of  cells,  which  in  the  vitreous  humor  are 
rounded,  and  in  the  jelly  of  the  enamel  organ  are  stellate,  imbedded 
in  a  soft  jelly-like  intercellular  substance  which  forms  the  bulk 
of  the  tissue,  and  which  contains  a  considerable  quantity  of  mucin.  In 
the  umbilical  cord,  that  part  of  the  jelly  immediately  surrounding  the 
stellate  cells  shows  marks  of  obscure  fibrillation  (Fig.  37). 

(b.)  Adenoid  or  Retiform. 

Distribution. — It  composes  the  stroma  of  the  spleen  and  lymphatic 
glands,  and  is  found  also  in  the  thymus,  in  the  tonsils,  in  the  follicular 


36 


HANDBOOK    OF    PHYSIOLOGY. 


glands  of  the  tongue,  in  Peyer's  patches  and  in  the  solitary  glands  of  the 
intestines,  and  in  the  mucous  membranes  generally. 

Structure. — Adenoid  or  retiform  tissue  consists  of  a  very  delicate  net- 
work of  minute  fibrils,  formed  originally  by  the  union  of  processes  of 
branched  connective-tissue  corpuscles  the  nuclei  of  which,  however,  are 
visible  only  during  the  early  periods  of  development  of  the  tissue  (Fig. 
38). 

The  nuclei  found  on  the  fibrillar  meshwork  do  not  form  an  essential 
part  of  it.  The  fibrils  are  neither  white  fibres  nor  elastic  tissue,  as  they 
are  insoluble  in  boiling  water,  although  readily  soluble  in  hot  alkaline 
solutions.  The  lymphoid  corpuscles  found  in  the  interstices  of  the  tis- 
sue are  small  round  cells,  the  protoplasm  of  which  is  practically  occupied 
by  their  spherical  nuclei. 

(c.)  Neuroglia. — This  tissue  forms  the  support  of  the  Nervous  ele- 


Fig.  39.— Portion  of  submucous  tissue  of  gravid  uterus  of  sow.    a,  branched  cells,  more  or  less 
spindle-shaped;  b,  bundles  of  connective  tissue.    (Klein. ) 

ments  in  the  Brain  and  Spinal  cord.  It  consists  of  a  very  fine  meshwork 
of  fibrils,  said  to  be  elastic,  and  with  nucleated  plates  which  constitute 
the  connective-tissue  corpuscles  imbedded  in  it. 


Development  of  Fibrous  Tissues. — In  the  embryo  the  place  of 
the  fibrous  tissues  is  at  first  occupied  by  a  mass  of  roundish  cells,  derived 
from  the  " meso blast."'' 

These  develop  either  into  a  network  of  branched  cells,  or  into  groups 
of  fusiform  cells  (Fig.  39). 

The  cells  are  imbedded  in  a  semi-fluid  albuminous  substance  derived 
either  from  the  cells  themselves  or  from  the  neighboring  blood-vessels  ; 
this  afterwards  forms  the  cement  substance.  In  it  fibres  are  developed, 
either  by  part  of  the  cells  becoming  fibrils,  the  others  remaining  as  con- 
nective-tissue corpuscles,  or  by  the  fibrils  being  developed  from  the  out- 
side layers  of  the  protoplasm  of  the  cells,  which  grow  up  again  to  their 
original  size  and  remain  imbedded  among  the  fibres.  The  process  gives 
rise  to  fibres  arranged  in  the  one  case  in  interlacing  networks  (areo- 
lar tissue),  in  the  other  in  parallel  bundles  (white  fibrous  tissue).  In 
the  mature  forms  of  purely  fibrous  tissue  not  only  the  remnants  of  the 


THE    STRUCTURE    <>F    THE    ELEMENTARY    TISSUES.  Oi 

cell-substance,  but  even  the  nuclei  may  disappear.  The  embryonic  tis- 
sue, from  which  elastic  fibres  are  developed,  is  composed  of  fusiform 
cells,  and  a  structureless  intercellular  substance  by  the  gradual  fibrilla- 
tion of  which  elastic  fibres  are  formed.  The  fusiform  cells  dwindle  in 
size  and  eventually  disappear  so  completely  that  in  mature  elastic  tissue 
hardly  a  trace  of  them  is  to  be  found:  meanwhile  the  elastic  fibres 
steadily  increase  in  size. 

Another  theory  of  the  development  of  the  connective-tissue  fibrils 
supposes  that  they  arise  from  deposits  in  the  intercellular  substance  and 
not  from  the  cells  themselves;  these  deposits,  in  the  case  of  elastic  fibres, 
appearing  first  of  all  in  the  form  of  rows  of  granules,  which,  joining 
together,  form  long  fibrils.  It  seems  probable  that  even  if  this  view  be 
correct,  the  cells  themselves  have  a  considerable  influence  in  the  produc- 
tion of  the  deposits  outside  them. 

Functions  of  Areolar  and  Fibrous  Tissue. — The  main  function 
of  connective  tissue  is  mechanical  rather  than  vital:  it  fulfils  the  subsidi- 
ary but  important  use  of  supporting  and  connecting  the  various  tissues 
and  organs  of  the  body. 

In  glands  the  trabecular  of  connective  tissue  form  an  interstitial  frame- 
work in  which  the  parenchyma  or  secreting  gland-tissue  is  lodged:  in 
muscles  and  nerves  the  septa  of  connective  tissue  support  the  bundles  of 
fibres  which  form  the  essential  part  of  the  structure. 

Elastic  tissue,  by  virtue  of  its  elasticity,  has  other  important  uses  : 
these,  again,  are  mechanical  rather  than  vital.  Thus  the  ligamentum 
nuchas  of  the  horse  or  ox  acts  very  much  as  an  India-rubber  baud  in  the 
same  position  would.  It  maintains  the  head  in  a  proper  position  with- 
out any  muscular  exertion;  and  when  the  head  has  been  lowered  by  the 
action  of  the  flexor  muscles  of  the  neck,  and  the  ligamentum  nuchas  thus 
stretched,  the  head  is  brought  up  again  to  its  normal  position  by  the  re- 
laxation of  the  flexor  muscles  which  allows  the  elasticity  of  the  ligamentum 
nuchas  to  come  again  into  play. 

(d.)  Adipose  Tissue. 

Distribution. — In  almost  all  regions  of  the  human  body  a  larger  or 
smaller  quantity  of  adipose  or  fatty  tissue  is  present;  the  chief  excep- 
tions being  the  subcutaneous  tissue  of  the  eyelids,  penis,  and  scrotum, 
the  nymphas,  and  the  cavity  of  the  cranium.  Adipose  tissue  is  also  ab- 
sent from  the  substance  of  many  organs,  as  the  lungs,  liver,  and  others. 

Fatty  matter,  not  in  the  form  of  a  distinct  tissue,  is  also  widely 
present  in  the  body,  e.g.,  in  the  liver  and  brain,  and  in  the  blood  and 
chyle. 

Adipose  tissue  is  almost  always  found  seated  in  areolar  tissue,  and 
forms  in  its  meshes  little  masses  of  unequal  size  and  irregular  shape,  to 
which  the  term  lobules  is  commonly  applied. 

Structure. — Under  the  microscope  adipose  tissue  is  found  to  consist 
essentially  of  little  vesicles  or  cells  which  present  dark,  sharply-defined 
edges  when  viewed  with  transmitted  light:  they  are  about  TJ-7  or  Tfo  of 
an  inch  in  diameter,  each  composed  of  a  structureless  and  colorless 
membrane  or  bag,  filled  with  fatty  matter,  which  is  liquid  during  life, 


38 


HANDBOOK    OF    PHYSIOLOGY. 


but  in  part  solidified  after  death  (Fig.  40).  A  nucleus  is  always  present 
in  some  part  or  other  of  the  cell-protoplasm,  but  in  the  ordinary  condi- 
tion of  the  cell  it  is  not  easily  or  always  visible. 


Fig.  40. 


Fig.  41. 


Fig.  40.— Ordinary  fat  cells  of  a  fat  tract  in  the  omentum  of  a  rat.     (Klein.) 
Fig.  41. — Group  of  fat  cells  (fc)  with  capillary  vessels  (c).    (Noble  Smith.) 

This  membrane  and  the  nucleus  can  generally  be  brought  into  view 
by  staining  the  tissue;  it  can  be  still  more  satisfactorily  demonstrated  by 
extracting  the  contents  of  the  fat-cells  with  ether,  when  the  shrunken. 


Fig.  42. 


Fig.  43. 


Fig.  42— Blood- vessels  of  adipose  tissue,  a.  Minute  flattened  fat-lobule,  in  which  the  vessels 
only  are  represented,  a,  the  terminal  artery;  v,  the  primitive  vein;  b,  the  fat- vesicles  of  one  border 
of  the  lobule  separately  represented,  x  100.  b.  Plan  of  the  arrangement  of  the  capillaries  (c)  on 
the  exterior  of  the  vesicles;  more  highly  magnified.    (Todd  and  Bowman.) 

Fig.  43. -A  lobule  of  developing  adipose  tissue  from  an  eight  months'  foetus,  a.  Spherical  or. 
from  pressure,  polyhedral  cells  with  large  central  nucleus,  surrounded  by  a  finely  reticulated  sub- 
stance staining  uniformly  with  haematoxylin.  6.  Similar  cells  with  spaces  from  which  the  fat  has 
been  removed  by  oil  of  cioves.  c.  Similar  cells  showing  how  the  nucleus  with  inclosing  protoplasm 
is  being  pressed  towards  periphery,  d.  Nucleus  of  endothelium  of  investigating  capillaries.  (Mc- 
Carthy.)   Drawn  by  Treves. 


THE    STRUCTURE    OK    THE    KI.EMKNTAEY    TI8S1   I  8= 


39 


shrivelled  membranes  remain  behind.  By  mutnal  pressure,  fat-cells 
come  to  assume  a  polyhedral  figure  (Fig.  41). 

The  ultimate  cells  are  held  together  by  capillary  blood-vessels  (Fig. 
42);  while  the  little  clusters  thus  formed  are  grouped  into  small  masses, 
and  held  so,  in  most  cases,  by  areolar  tissue. 

The  oily  matter  contained  in  the  cells  is  composed  chiefly  of  the  com- 
pounds of  fatty  acids  with  glycerin,  which  are  named  ohin,  stearin,  and 
palmitin. 

Development  of  Adipose  Tissue. — Fat-cells  are  developed  from 
connective-tissue  corpuscles:  in  the  infra-orbital  connective  tissue  cells 
may  be  found  exhibiting  every  intermediate  gradation  between  an  ordi- 
nary branched  counective-tissue  corpuscle  and  a  mature  fat-cell.  The 
process  of  development  is  as  follows:  a  few  small  drops  of  oil  make  their 
appearance  in  the  protoplasm:  by  their  confluence  a  larger  drop  is  pro- 
duced (Fig.  43):  this  gradually  increases  in  size  at  the  expense  of  the 
original  protoplasm  of  the  cell,  which  becomes  correspondingly  dimin- 


Fig.  44.— Branched  connective-tissue  corpuscles,  developing  into  fat-cells.     (Klein. ) 

ished  ill  quantity  till  in  the  mature  cell  it  only  forms  a  thin  crescentic 
film,  closely  pressed  against  the  cell-wall,  and  with  a  nucleus  imbedded 
in  its  substance  (Figs.  43 .and  44). 

Under  certain  circumstances  this  process  may  be  reversed  and  fat- 
cells  maybe  changed  back  into  connective-tissue  corpuscles.  (Kolliker, 
Virchow.) 

Vessels  and  Nerves. — A  large  number  of  blood-vessels  are  found  in 
adipose  tissue,  which  subdivide  until  each  lobule  of  fat  coutains  a  Rue 
meshwork  of  capillaries  ensheathing  each  individual  fat-globule  (Fig. 
42).  Although  nerve  fibres  pass  through  the  tissue,  no  nerves  have  been 
demonstrated  to  terminate  in  it. 

The  Uses  of  Adipose  Tissue. — Among  the  uses  of  adipose  tissue, 
these  are  the  chief: — 

a.  It  serves  as  a  store  of  combustible  matter  which  may  he  re-absorbed 
into  the  blood  when  occasion  requires,  and.  being  burnt,  may  help  to 
preserve  the  heat  of  the  body. 

b.  That  part  of  the  fat  which  is  situate  beneath  the  skin  must,  by  its 
want  of  conducting  power,  assist  in  preventing  undue  waste  of  the  heat 
of  the  body  by  escape  from  the  surface. 


40 


HANDBOOK    OF    PHYSIOLOGY. 


e.  As  a  packing  material,  fat  serves  very  admirably  to  fill  up  spaces, 
to  form  a  soft  and  yielding  yet  elastic  material  wherewith  to  wrap  tender 
and  delicate  structures,  or  form  a  bed  with  like  qualities  on  which  such 
structures  may  lie,  not  endangered  by  pressure. 

As  good  examples  of  situations  in  which  fat  serves  such  purposes  may 
be  mentioned  the  palms  of  the  hands  and  soles  of  the  feet,  and  the 
orbits. 

d.  In  the  long  bones,  fatty  tissue,  in  the  form  known  as  yellow 
marrow,  fills  the  medullary  canal,  and  supports  the  small  blood-vessels 
which  are  distributed  from  it  to  the  inner  part  of  the  substance  of  the 
bone. 

II.  Cartilage. 

Structure  of  Cartilage. — All  kinds  of  cartilage  are  composed  of 
cells  imbedded  in  a  substance  called  the  matrix :  and  the  apparent  differ- 
ences of  structure  met  with  in  the  various  kinds  of  cartilage  are  more  due 


<S=* 


-SV'iu  il'V-.'liuilli'l'1' 


Fig.  45. 

Fig.  45. — Ordinary  hyaline  cartilage  from  trachea  of  a  child, 
singly  or  in  pairs  in  a  capsule  of  hyaline  substance,    x  150  diams. 
Fig.  46.— Fresh  cartilage  from  the  Triton.    (A  Rollett.) 


Fig.  46. 

The  cartilage  cells  are  inclosed 
(Klein  and  Noble  Smith. ) 


to  differences  in  the  character  of  the  matrix  than  of  the  cells.  Among 
the  latter,  however,  there  is  also  considerable  diversity  of  form  and  size. 

With  the  exception  of  the  articular  variety,  cartilage  is  invested  by  a 
thin  but  tough  firm  fibrous  membrane  called  the  perichondrium.  On 
the  surface  of  the  articular  cartilage  of  the  foetus,  the  perichondrium  is 
represented  by  a  film  of  epithelium;  but  this  is  gradually  worn  away  up 
to  the  margin  of  the  articular  surfaces,  when  by  use  the  parts  begin  to 
.suffer  friction. 

Nerves  are  probably  not  supplied  to  any  variety  of  cartilage. 

Cartilage  exists  in  three  different  forms  in  the  human  body,  viz.,  1, 
Hyaline  cartilage,  2,  Yellow  elastic  cartilage,  ami  3,  White  fibro-cartilage. 

1.  Hyaline  Cartilage. 

Distribution.— This  variety  of  cartilage  is  met  with  largely  in  the 


THE    STKL'CTUKK   OF    THE    KLEMENTAKY    TISSUES.  41 

human  body — investing  the  articular  vnd*  of  bones,  and  forming  the 
costal  cartilages,  the  nasal  cartilages,  and  those  of  the  larynx  with  the 
exception  of  the  epiglottis  and  cornicula  laryngis,  as  well  as  those  of  the 
trachea  and  bronchi. 

Structure. — Like  other  cartilages  it  is  composed  of  cells  imbedded  in 
a  matrix.  The  cells,  which  contain  a  nucleus  with  nucleoli,  are  irregu- 
lar in  shape,  and  generally  grouped  together  in  patches  (Fig.  45).  The 
patches  are  of  various  shapes  and  sizes,  and  placed  at  unequal  distances 
apart.  They  generally  appear  flattened  near  the  free  surface  of  the  mass 
of  cartilage  in  which  they  are  placed,  and  more  or  less  perpendicular  to 
the  surface  in  the  more  deeply-seated  portions. 

The  matrix  of  hyaline  cartilage  has  a  dimly  granular  appearance  like 
that  of  ground  glass,  and  in  man  and  the  higher  animals  has  no  apparent 
structure.  In  some  cartilages  of  the  frog,  however,  even  when  examined 
in  the  fresh  state,  it  is  seen  to  be  mapped  out  into  polygonal  blocks  or 
cell-territories,  each  containing  a  cell  in  the  centre,  and  representing 
what  is  generally  called  the  capsule  of  the  cartilage  cells  (Fig.  46). 
Hyaline  cartilage  in  man  has  really  the  same  structure,  which  can  be 
demonstrated  by  the  use  of  certain  reagents.  If  a  piece  of  human  hya- 
line cartilage  be  macerated  for  a  long  time  in  dilute  acid  or  in  hot  water 
95°-113°  F.  (35°  to  45°  C),  the  matrix,  which  previously  appeared 
quite  homogeneous,  is  found  to  be  resolved  into  a  number  of  concentric 
lamellae,  like  the  coats  of  an  onion,  arranged  round  each  cell  or  group  of 
cells.  It  is  thus  shown  to  consist  of  nothing  but  a  number  of  large 
systems  of  capsules  which  have  become  fused  with  one  another. 

The  cavities  in  the  matrix  in  which  the  cells  lie  are  connected  to- 
gether by  a  series  of  branching  canals,  very  much  resembling  those  in 
the  cornea:  through  these  canals  fluids  may  make  their  way  into  the 
depths  of  the  tissue. 

In  the  hyaline  cartilage  of  the  ribs,  the  cells  are  mostly  larger  than 
in  the  articular  variety,  and  there  is  a  tendency  to  the  development  of 
fibres  in  the  matrix  (Fig.  47).  The  costal  cartilages  also  frequently  be- 
come calcified  in  old  age,  as  also  do  some  of  those  of  the  larynx.  Fat- 
globules  may  also  be  seen  in  many  cartilages  (Fig.  47). 

In  articular  cartilage  the  cells  are  smaller,  and  arranged  vertically  in 
narrow  lines  like  strings  of  beads. 

Temporary  Cartilage. — in  the  foetus,  cartilage  is  the  material  of 
which  the  bones  are  first  constructed;  the  "  model  "  of  each  bone  being 
laid  down,  so  to  speak,  in  this  substance.  In  such  cases  the  cartilage  is 
termed  temporary.  It  closely  resembles  the  ordinary  hyaline  kind; 
the  cells,  however,  are  not  grouped  together  after  the  fashion  just 
-described,  but  are  more  uniformly  distributed  throughout  the  matrix. 

A   variety    of    temporary  hyaline    cartilage  which  has  scarcely  any 


42 


HANDBOOK    OF    PHYSIOLOGY. 


matrix  is  found  in  the  human  subject  and  in  the  higher  animals  gene- 
rally, in  early  foetal  life,  when  it  constitutes  the  chorda  dorsalis. 

Nutrition. — Hyaline  cartilage  is  reckoned  among  the  so-called  non- 
vascular structures,  no  blood-vessels  being  supplied  directly  to  its  own 
substance;  it  is  nourished  by  those  of  the  bone  beneath.  When  hyaline 
cartilage  is  in  thicker  masses,  as  in  the  case  of  the  cartilages  of  the  ribs, 
a  few  blood-vessels  traverse  its  substance.  The  distinction,  however, 
between  all  so-called  vascular  and  non-vascular  parts  is  at  the  best  a 
very  artificial  one. 

2.  Yellow  Elastic  Cartilage. 

Distribution. — In  the  external  ear,  in  the  epiglottis  and  cornicula 
laryngis,  and  in  the  Eustachian  tube. 

Structure. — The  cells  are  rounded  or  oval,  with  well-marked  nuclei 
or  nucleoli  (Fig.  48).  The  matrix  in  which  they  are  seated  is  composed 
almost  entirely  of  fine  elastic  fibres,  which  form  an  intricate  interlace- 

IIIlllllllIW 


Fig.  48. 

Fig.  47  —  Costal  cartilage  from  au  adult  dog,  shoeing  the  fat  globules  in  the  cartilage  cells. 
(Cadiat. ) 

Fig.  48— Section  of  the  epiglottis.     <  Baly. ) 

ment  about  the  cells-,  and  in  their  general  characters  are  allied  to  the 
yellow  variety  of  fibrous  tissue:  a  small  and  variable  quantity  of  hya- 
line and  intercellular  substance  is  also  usually  present. 

A  variety  of  elastic  cartilage,  sometimes  called  cellular,  may  be  ob- 
tained from  the  external  ear  of  rats,  mice,  or  other  small  mammals. 
It  is  composed  almost  entirely  of  cells  (hence  the  name),  which  are 
packed  very  closely,  with  little  or  no  matrix.  When  present,  the  matrix 
consists  of  very  fine  fibres,  which  twine  about  the  cells  in  various  direc- 
tions and  inclose  them  in  a  kind  of  network.  Elastic  cartilage  seldom 
or  never  ossifies. 

3.  White  Fibro-Cartilage. 

Distribution. — The  different  situations  in  which  white  fibro-car- 
tilage  is  found  have  given  rise  to  the  following  classification: — 


THE   STRUCTURE    OF  THE    ELEMENTARY  TISSUES.  ±6 

1.  Inter-articular  fibro-cartilage,  e.  g.,  the  semilunar  cartilages  of 
the  knee-joint. 

2.  Circumferential  or  marginal,  as  on  the  edges  of  the  acetabulum 
and  glenoid  cavity. 

3.  Connecting,  e.  g.,  the  intervertebral  fibro-cartilages. 

4.  In  the  sheaths  of  tendons,  and  sometimes  in  their  substance.  In 
the  latter  situation,  the  nodule  of  fibro-cartilage  is  called  a  sesamoid 
fibro-cartilage,  of  which  a  specimen  may  be  found  in  the  tendon  of  the 
tibialis  posticus,  in  the  sole  of  the  foot,  and  usually  in  the  neighboring 
tendon  of  the  peroneus  longus. 

Structure. — White  fibro-cartilage  (Fig.  49),  which  is  much  more 
widely  distributed  throughout  the  body  than  the  foregoing  kind,  is  com- 
posed, like  it,  of  cells  and  a  matrix;  the  latter,  however,  being  made 


Fig.  49. 


Fig.  50. 


Fig.  49. — Transverse  section  through  the  intervertebral  cartilage  of  tail  of  mouse,  showing 
lamella.*  of  fibrous  tissue  with  cartilage  cells  arranged  in  rows  between  them.  The  cells  ar  *  seen  in 
profile,  and  being  flattened,  appear  staff-shaped.  Each  cell  lies  in  a  capsule.  X  330.  ( Klein  and 
Noble  Smith.) 

Fig.  50.    White  fibro-cartilage  from  an  intervetebral  ligament.     (Klein  and  Noble  Smith  J 

up  almost  entirely  of  fibres  closely  resembling  those  of  white  fibrous 
tissue. 

In  this  kind  of  fibro-cartilage  it  is  not  unusual  to  find  a  great  part  of 
its  mass  composed  almost  exclusively  of  fibres,  and  deriving  the  name  of 
cartilage  only  from  the  fact  that  in  another  portion,  continuous  with  it, 
cartilage  cells  may  be  pretty  freely  distributed. 

By  prolonged  boiling,  cartilage  yields  a  gelatinous  substance  called 
chondrin — white  fibro-cartilasre  yields  gelatin  as  well. 


Functions  of  Cartilage. — Cartilage  not  only  represents  in  the  foetus 
the  bones  which  are  to  be  formed  (temporary  cartilage),  but  also  offers 
a  firm,  but  more  or  less  yielding,  framework  for  certain  parts  in  the  de- 
veloped body,  possessing  at  the  same  time  strength  and  elasticity.  It 
maintains  the  shape  of  tubes  as  in  the  larynx  and  trachea.  It  affords  at- 
tachment to  muscles  and  ligaments;  it  binds  bones  together,  yet  allows  a 
certain  degree  of  movement,  as  between  the  vertebras;  it  forms  a  firm 


44  HANDBOOK    OF    PHYSIOLOGY. 

framework  and  protection,  yet  without  undue  stiffness  or  weight,  as  in 
the  pinna,  larynx,  and  chest-walls;  it  deepens  joint  cavities,  as  in  the 
acetabulum,  without  unduly  restricting  the  movements  of  the  bones. 

Development  of  Cartilage. — Cartilage  is  developed  out  of  an  em- 
bryonal tissue,  consisting  of  cells  with  a  very  small  quantity  of  intercel- 
lular substance:  the  cells  multiply  by  fission  within  the  cell-capsules  (Fig. 
■6);  while  the  capsule  of  the  parent  cell  becomes  gradually  fused  with  the 
surrounding  intercellular  substance.  A  repetition  of  this  process  in  the 
young  cells  causes  a  rapid  growth  of  the  cartilage  by  the  multiplication 
of  its  cellular  elements  and  corresponding  increase  in  its  matrix.  Thus 
we  see  that  the  matrix  of  cartilage  is  chiefly  derived  from  the  cartilage 
«ells. 

III.  Bone. 

Chemical  Composition. — Bone  is  composed  of  earthy  and  animal  mat- 
ter in  the  proportion  of  about  G7  per  cent  of  the  former  to  33  per  cent 
of  the  latter.  The  earthy  matter  is  composed  chiefly  of  calcium  phos- 
phate, but  besides  there  is  a  small  quantity  (about  11  of  the  67  percent) 
of  calcium  carbonate  and  fluoride,  and  magnesium  phosphate. 

The  animal  matter  is  resolved  into  gelatin  by  boiling. 

The  earthy  and  animal  constituents  of  bone  are  so  intimately  blended 
and  incorporated  the  one  with  the  other,  that  it  is  only  by  chemical  ac- 
tion, as,  for  instance,  by  heat  in  one  case  and  by  the  action  of  acids  in 
another,  that  they  can  be  separated.  Their  close  union,  too,  is  further 
shown  by  the  fact  that  when  by  acids  the  earthy  matter  is  dissolved  out, 
or,  on  the  other  hand,  when  the  animal  part  is  burnt  out,  the  shape  of 
the  bone  is  alike  preserved. 

The  proportion  between  these  two  constituents  of  bone  varies  in  dif- 
ferent bones  in  the  same  individual,  and  in  the  same  bone  at  different 


Structure. — To  the  naked  eye  there  appear  two  kinds  of  structure  in 
different  bones,  and  in  different  parts  of  the  same  bone,  namely,  the 
dense  or  compact,  and  the  spongy  or  cancellous  tissue. 

Thus,  in  making  a  longitudinal  section  of  a  long  bone,  as  the  humerus 
or  femur,  the  articular  extremities  are  found  capped  on  their  surface  by 
a  thin  shell  of  compact  bone,  while  their  interior  is  made  up  of  the 
spongy  or-  cancellous  tissue.  The  shaft,  on  the  other  hand,  is  formed 
almost  entirely  of  a  thick  layer  of  the  compact  bone,  and  this  surrounds 
a  central  canal,  the  medullary  cavity — so  called  from  its  containing  the 
medulla  or  marrow. 

In  the  flat  bones,  as  the  parietal  bone  or  the  scapula,  one  layer  of  the 
cancellous  structure  lies  between  two  layers  of  the  compact  tissue,  and 
in  the  short  and  irregular  bones,  as  those  of  the  carpus  and  tarsus,  the 
cancellous  tissue  alone  fills  the  interior,  while  a  thin  shell  of  compact 
bone  forms  the  outside. 

Marrow. — There  are  two  distinct  varieties  of  marrow — the  red  and 
yellow. 


THE    STBUCTTTKE    OF    THE    ELEMENTARY    TISSUES. 


4:5 


Red  marrow  is  that  variety  which  occupies  the  spaces  in  the  cancel- 
lous tissue;  it  is  highly  vascular,  and  thus  maintains  the  nutrition  of 
the  spongy  bone,  the  interstices  of  which  it  tills.  It  contains  a  few  fat- 
cells  and  a  large  number  of  marrow-cells,  many  of  which  are  undistin- 
guishable  from  lymphoid  corpuscles,  and  has  for  a  basis  a  small  amount 
of  fibrous  tissue.  Among  the  cells  are  some  nucleated  cells  of  very  much 
the  same  tint  as  colored  blood-corpuscles.  There  are  also  a  few  large 
cells  with  many  nuclei,  termed  "  giant-  eel  Is  "  (myeloplaxes),  which  are 
derived  from  over-growth  of  the  ordinary  marrow-cells  (Fig.  51). 

Yellow  marrow  fills  the  medullary  cavity  of  long  bones,  and  consists 
chiefly  of  fat-cells  with  numerous  blood-vessels;  many  of  its  cells  also 
are  in  every  respect  similar  to  lymphoid  corpuscles. 

From  these  marrow-cells,  especially  those  of  the  red  marrow,  are 


Fig.  51.-  Cells  of  the  red  marrow  of  the  guinea  pig,  highly  magnified,  a,  a  large  cell,  the 
nucleus  of  which  appears  to  be  partly  divided  into  three  by  constrictions  ;  b,  a  cell,  the  nucleus  of 
which  shows  an  appearance  of  being  constricted  into  a  number  of  smaller  nuclei;  c,  a  so-called 
gjanb  cell,  or  myeloplaxe,  with  many  nuclei ;  d,  a  smaller  1113-eloplaxe,  with  three  nuclei ;  e—i, 
proper  cells  of  the  marrow.     (E.  A.  Sehiifer.) 

derived,  as  we  shall  presently  show,  large  quantities  of  red  blood- 
corpuscles. 

Periosteum  and  Nutrient  Blood-vessels. — The  surfaces  of  the 
bones,  except  the  part  covered  with  articular  cartilage,  are  clothed  by  a 
tough,  fibrous  membrane,  the  periosteum ;  and  it  is  from  the  blood- 
vessels which  are  distributed  in  this  membrane,  that  the  bones,  especially 
their  more  compact  tissue,  are  in  great  part  supplied  with  nourishment, 
— minute  branches  from  the  periosteal  vessels  entering  the  little  fora- 
mina on  the  surface  of  the  bone,  and  finding  their  way  to  the  Haver- 
sian canals,  to  be  immediately  described.  The  long  bones  are  supplied 
also  by  a  proper  nutrient  artery  which,  entering  at  some  part  of  the 
shaft  so  as  to  reach  the  medullary  canal,  breaks  up  into  branches  for  the 
supply  of  the  marrow,  from  which  again  small  vessels  are  distributed  to 
the  interior  of  the  bone.  Other  small  blood-vessels  pierce  the  articular 
extremities  for  the  supply  of  the  cancellous  tissue. 

Microscopic  Structure  of  Bone. — Notwithstanding  the  differences  of 


46 


HANDBOOK   OF    PHYSIOLOGY. 


arrangement  just  mentioned,  the  structure  of  all  bone  is  found  under 
the  microscope  to  be  essentially  the  same. 

Examined  with  a  rather  high  power,  its  substance  is  found  to  contain 
a  multitude  of  small  irregular  spaces,  approximately  fusiform  in  shape, 
called  lacunce,  with  very  minute  canals  or  canaliculi,  as  they  are  termed, 
leading  from  them,  and  anastomosing  with  similar  little  prolongations 
from  other  lacunae  (Fig.  52).  In  very  thin  layers  of  bone,  no  other  canals 
than  these  may  be  visible;  but  on  making  a  transverse  section  of  the 
compact  tissue  as  of  a  long  bone,  e.  g.,  the  humerus  or  ulna,  the  arrange- 
ment shown  in  Fig.  52,  can  be  seen. 

The  bone  seems  mapped  out  into  small  circular  districts,  at  or  about 
the  centre  of  each  of  which  is  a  hole,  and  around  this  an  appearance  as 
of  concentric  layers — the  lacunw  and  canaliculi  following  the  same  con- 


Fig.  52.— Transverse  section  of  compact  bony  tissue  (of  humerus*.  Three  of  the  Haversian 
<canals  are  seen,  with  their  concentric  rings  ;  also  the  corpuscles  or  lacunae,  with  the  canaliculi  ex- 
tending from  them  across  the  direction  of  the  lamellae.  The  Haversian  apertures  had  got  filled 
with  debris  in  grinding  down  the  section,  and  therefore  appear  black  in  the  figure,  which  represents 
the  object  as  viewed  with  transmitted  light.  The  Haversian  systems  are  so  closely  packed  in  this 
section,  that  scarcely  any  interstitial  lamellae  are  visible.     X  150.    (Sharpey.) 


centric  plan  of  distribution  around  the  small  hole  in  the  centre,  with 
which,  indeed,  they  communicate. 

On  making  a  longitudinal  section,  the  central  holes  are  found  to  be 
simply  the  cut  extremities  of  small  canals  which  run  lengthwise  through 
the  bone,  anastomosing  with  each  other  by  lateral  branches  (Fig.  53), 
and  are  called  Haversian  canals,  after  the  name  of  the  physician,  Clop- 
ton  Havers,  who  first  accurately  described  them.  The  Haversian  canals, 
the  average  diameter  of  which  is  ^i^  of  an  inch,  contain  blood-vessels, 
and  by  means  of  them  blood  is  conveyed  to  all,  even  the  densest  parts  of 
the  bone;  the  minute  canaliculi  and  lacunas  absorbing  nutrient  matter 


THE    STKUCTUKE    OF  THE    ELEMENTARY    TISSUES. 


47 


from  the  Haversian  blood-vessels,  and  conveying  it  still  more  intimately 
to  the  very  substance  of  the  bone  which  they  traverse. 

The  blood-vessels  enter  the  Haversian  canals  both  from  without,  by 
traversing  the  small  holes  which  exist  on  the  surface  of  all  bones  beneath 
the  periosteum,  and  from  within  by  means  of  small  channels  which  extend 
from  the  medullary  cavity,  or  from  the  cancellous  tissue.  The  arteries 
and  veins  usually  occupy  separate  canals,  and  the  veins,  which  are 
the  larger,  often  present,  at  irregular  intervals,  small  pouch-like  dilata- 
tions. 

The  lacuna  are  occupied  by  branched  cells  (bone-cells,  or  bone-cor- 
puscles) (Fig.  54),  which  very  closely  resemble  the  ordinary  branched 
connective-tissue  corpuscles;  each  of  these  little  masses  of  protoplasm 


Fig.  53. 


Fio    54. 


Fig.  53.— Longitudinal  section  of  human  ulna,  showing  Haversian  canal,  lacunae,  and canaliculi. 
(Rollett.) 

Fig.  54.— Bone-corpuscles  with  their  processes  as  seen  in  a  thin  section  of  human  bone.  (Uollett.) 

ministering  to  the  nutrition  of  the  bone  immediately  surrounding  it, 
and  one  lacunar  corpuscle  communicating  with  another,  and  with  its 
surrounding  district,  and  with  the  blood-vessels  of  the  Haversian  canals, 
by  means  of  the  minute  streams  of  fluid  nutrient  matter  which  occupy 
the  canaliculi. 

It  will  be  seen  from  the  above  description  that  bone  is  essentially 
connective  tissue  impregnated  with  lime  salts:  it  bears  a  very  close 
resemblance  to  what  may  be  termed  typical  connective  tissue  such  as  the 
substance  of  the  cornea.  The  bone-corpuscles  with  their  processes, 
occupying  the  lacunas  and  canaliculi,  correspond  exactly  to  the  cornea- 
corpuscles  lying  in  branched  spaces;  while  the  finely  tibrillated  structure 


48 


HANDBOOK    OF    PHYSIOLOGY. 


of  the  bone-lamellae,  to  be  presently  described,  resembles  the  fibrillated 
substance  of  the  cornea  in  which  the  branching  spaces  lie. 

Lamellae  of  Compact  Bone. — In  the  shaft  of  a  long  bone  three 
distinct  sets  of  lamellae  can  be  clearly  recognized. 

(1.)  General  or  fundamental  lamella?;  which  are  most  easily  traceable 
just  beneath  the  periosteum,  and  around  the  medullary  cavity,  forming 
around  the  latter  a  series  of  concentric  rings.  At  a  little  distance  from 
the  medullary  and  periosteal  surfaces  (in  the  deeper  portions  of  the  bone) 
they  are  more  or  less  interrupted  by 

(2.)  Special  or  Haversian  lamellae,  which  are  concentrically  arranged 
around  the  Haversian  canals  to  the  number  of  six  to  eighteen  around 
each. 

(3.)  Interstitial  lamellse,  which  connect  the  systems  of  Haversian 


Fig.  55. 


Fig.  56. 


Fig.  55.— Thin  layer  peeled  off  from  a  softened  bone.  This  figure,  which  is  intended  to  represent 
the  reticular  structure  of  a  lamella,  gives  a  better  idea  of  the  object  when  held  rather  farther  off 
than  usual  from  the  eye.     X  400.    (Sharpey.) 

Fig.  50.  —Lamellae  torn  off  from  a  decalcified  human  parietal  bone  at  some  depth  from  the  surface, 
a,  a  lamella,  showing  reticular  fibres  ;  6,  6,  darker  part,  where  several  lamellae  are  superposed ; 
c,  perforating  fibres.  Apertures  though  which  perforating  fibres  had  passed,  are  seen  especially  in 
the  lower  part,  a,  a,  of  the  figure.    (Allen  Thomson.) 

lamellae,  filling  the  spaces  between  them,  and  consequently  attaining 
their  greatest  development  where  the  Haversian  systems  are  few,  and 
vice  versd. 

The  ultimate  structure  of  the  lamellm  appears  to  be  reticular.  If  a 
thin  film  be  peeled  off  the  surface  of  a  bone,  from  which  the  earthy 
matter  has  been  removed  by  acid,  and  examined  with  a  high  power  of 
the  microscope,  it  will  be  found  composed  of  a  finely  reticular  structure, 
formed  apparently  of  very  slender  fibres  decussating  obliquely,  but  coa- 
lescingrat  the  points  of  intersection,  as  if  here  the  fibres  were  fused 
rather  than  woven  together  (Fig.  55).     (Sharpey.) 


THE    STRUCTURE    OF    THE    ELEMENTARY    TISSUES.  49 

In  many  places  these  reticular  lamellae  are  perforated  by  tapering 
fibres  (Claviculi  of  Gagliardi),  resembling  in  character  the  ordinary 
white  or  rarely  the  elastic  fibrous  tissue,  which  bolt  the  neighboring 
lamellae  together,  and  may  be  drawn  out  when  the  latter  are  torn  asunder 
(Fig.  5G).  These  perforating  fibres  originate  from  ingrowing  processes 
of  the  periosteum,  and  in  the  adult  still  retain  their  connection  with  it. 

Development  of  Bone.  — From  the  point  of  view  of  their  develop- 
ment, all  bones  may  be  subdivided  into  two  classes. 

(a.)  Those  which  are  ossified  directly  in  membrane  or  fibrous  tissue, 
e.  g.,  the  bones  forming  the  vault  of  the  skull,  parietal,  frontal. 

(b.)  Those  whose  form,  previous  to  ossification,  is  laid  down  in  hy- 
aline cartilage,  e.  g.,  humerus,  femur. 

The  process  of  development,  pure  and  simple,  may  be  best  studied  in 
bones  which  are  not  preceded  by  cartilage  —  '•  membrane-bones"  (e.  g., 
parietal)  ;  and  without  a  knowledge  of  this  process  (ossification  in  mem- 
brane), it  is  impossible  to  understand  the  much  more  complex  series  of 
changes  through  which  such  a  structure  as  the  cartilaginous  femur  of 
the  foetus  passes  in  its  transformation  into  the  bony  femur  of  the  adult 
(ossification  in  cartilage). 

Ossification  in  Membrane.— The  membrane,  afterwards  forming 
the  periosteum,  from  which  such  a  bone  as  the  parietal  is  developed, 
consists  of  two  layers — an  external  fibrous,  and  an  internal  cellular  or 
osteo-genetic. 

The  external  one  consists  of  ordinary  connective  tissue,  being  com- 
posed of  layers  of  fibrous  tissue  with  branched  connective-tissue  corpus- 
cles here  and  there  between  the  bundles  of  fibres.  The  internal  layer 
consists  of  a  network  of  fine  fibrils  with  a  large  number  of  nucleated 
cells,  some  of  which  are  oval,  others  drawn  out  into  a  long  branched 
process,  and  others  branched  :  it  is  more  richly  supplied  with  capillaries 
than  the  outer  layer.  The  relatively  large  number  of  its  cellular  ele- 
ments, which  vary  in  size  and  shape,  together  with  the  abundance  of  its 
blood-vessels,  clearly  mark  it  out  as  the  portion  of  the  periosteum  which 
is  immediately  concerned  in  the  formation  of  bone. 

In  such  a  bone  as  the  parietal,  the  deposition  of  bony  matter,  which 
is  preceded  by  increased  vascularity,  takes  place  in  radiating  spiculae, 
starting  from  a  "  centre  of  ossification/'  and  shooting  out  in  all  direc- 
tions towards  the  periphery.  While  the  bone  increases  in  thickness  by 
the  deposition  of  successive  layers  beneath  the  periosteum,  in-growths 
of  the  osteogenetic  layer  of  the  periosteum  take  place,  and  it  is  by  the 
action  of  their  osteoblasts  that  bone  is  secreted  at  a  centre  of  ossification. 
The  osteoblasts,  being  in  part  retained  within  the  primary  bone  trabec- 
ule thus  produced,  forming  bone  corpuscles.  It  is  doubtful  what  part 
the  finely  fibrillar  part  of  the  osteogenetic  iu-growth  takes  in  the  forma- 
tion of  the  trabecular  probably  it  supplies  the  reticular  matrix  of  the 
4 


50 


HANDBOOK    OF   PHYSIOLOGY. 


new-formed  bone.  On  the  bony  trabecular  first  formed,  fresh  layers  of 
cells  (osteoblasts)  from  the  osteogenetic  layer  are  developed  side  by  side, 
lining  the  irregular  spaces  like  an  epithelium  (Fig.  57,  b).  Lime-salts 
are  deposited  in  the  circumferential  part  of  each  osteoblast,  and  thus  a 
ring  of  osteoblasts  give  rise  to  a  ring  of  bone  with  the  remaining  uncal- 
cified  portions  of  the  osteoblasts  imbedded  in  it  as  bone  corpuscles,  as  in 
the  first  formation. 

Thus,  the  primitive  spongy  bone  is  formed,  whose  irregular  branch- 
ing spaces  are  occupied  by  processes  from  the  osteogenetic  layer  of  the 
periosteum  with  numerous  blood-vessels  and  osteoblasts.  Portions  of 
this  primitive  sjjongy  bone  are  re-absorbed  ;  the  osteoblasts  being  ar- 


Fig.  57. 


Fig.  58. 


Fig.  57.— Osteoblasts  from  the  parietal  bone  of  a  human  embryo,  thirteen  weeks  old.  a,  bony- 
septa  with  the  cells  of  the  lacunae;  b,  layers  of  osteoblasts;  c,  the  latter  in  transition  to  bone  cor- 
puscles.   Highly  magnified.     (Gegenbaur. ) 

Fig.  58.  —From  a  transverse  section  through  part  of  the  f  cetal  jaw  near  the  extreme  periosteum 
in  the  state  of  spongy  bone.  »,  fibrous  layer  of  periosteum,  b,  osteogenetic  layer  of  periosteum; 
o,  osteobiasts;  c,  osseous  substance,  containing  many  bone  corpuscles.     X  3J0.    (SchofieldJ 

ranged  in  concentric  successive  layers  and  thus  giving  rise  to  concentric 
Haversian  lamellee  of  bone,  until  the  irregular  space  in  the  centre  is 
reduced  to  a  well-formed  Haversian  canal,  the  portions  of  the  primitive 
spongy  bone  between  the  Haversian  systems  remaining  as  interstitial  or 
ground  lamella?  (p.  48).  The  bulk  of  the  primitive  spongy  bone  is  thus 
gradually  converted  into  compact  bony  tissue  with  Haversian  canals. 
Those  portions  of  the  in-growths  from  the  deeper  layer  of  the  periosteum 


THE    STRUCTURE    OF    THE    ELEMENTARY    TISSUES. 


51 


which  are  not  converted  into  bone  remain  in  the  spaces  of  the  cancellous 
tissue  as  the  red  marrow. 

Ossification  in  Cartilage.— Under  this  heading,  taking  the  femur 
as  a  typical  example,  we  may  consider  the  process  by  which  the  solid 
cartilaginous  rod  which  represents  it  in  the  fcetus  is  converted  into  the 
hollow  cylinder  of  compact  bone  with  expanded  ends  of  cancellous  tissue 


^ 


p 


Fig.  59. 


/n^( 


Fig.  60. 


Fig.  59.—  Ossifying  cartilage  showing  loops  of  blood-vessels. 

Fig.  tin. -Longitudinal  section  of  ossifying  cartilage  from  the  humerus  of  a  fu»tal  Sheep.  Cal- 
cified trabeculse  are  seen  extending  between  the  the  columns  of  cartilage  cells,  c,  cartdage  cells. 
x  140.    i  Sharpey.  > 

which  forms  the  adult  femur;  bearing  iu  mind  the  fact  that  this  foetal 
cartilaginous  femur  is  many  times  smaller  than  the  medullary  cavity 
even  of  the  shaft  of  the  mature  bone,  and,  therefore,  that  not  a  trace  of 
the  original  cartilage  can   be   present   in  the  femur  of  the  adult.     Its 


52 


HANDBOOK    OF   PHYSIOLOGY. 


purpose  is  indeed  purely  temporary;  and,  after   its  calcification,  it  is 
gradually  and  entirely  absorbed  as  will  be  presently  explained. 

The  cartilaginous  rod  which  forms  the  foetal  femur  is  sheathed  in  a 
membrane  termed  the  perichondrium,  which  so  far  resembles  the  peri- 
osteum described  above,  that  it  consists  of  two  layers,  in  the  deeper  one 
of  which  spheroidal  cells  predominate  and  blood-vessels  abound,  while 
the  outer  layer  consists  mainly  of  fusiform  cells  which  are  in  the  mature 
tissue  gradually  transformed  into  fibres.  Thus,  the  differences  between 
the  foetal  perichondrium  and  the  periosteum  of  the  adult  are  such  as 
usually  exist  between  the  embryonic  and  mature  forms  of  connective 
tissue. 


Fig.  61. 


Fig.  62. 


Fig.  61. — Transverse  section  of  a  portion  of  metacarpal  bone  of  a  foetus,  showing-— 1,  fibrous 
layer  of  periosteum;  2,  osteogenetic  layer  of  ditto;  3  periosteal  bone;  4,  cartilage  with  matrix  grad- 
ually becoming  calcified,  as  at  5,  with  cells  in  primary  areolae ;  beyond  5  the  calcified  matrix  is 
being:  entirely  replaced  by  spongy  bone.     X  2  0.    ( V.  D.  Harris.) 

Fig.  62.  A  small  isolated  mass  of  bone  next  the  perio-teum  of  the  lower  jaw  of  human  foetus. 
a,  osteogenetic  layer  of  periosteum.  G,  multinuelear  giant  cells,  the  one  on  the  left  acting  here 
probably  like  an  osteoclast  Above  c,  the  osteoblasts  are  seen  to  become  surrounded  by  an  osse- 
ous matrix.    (K.ein  and  Noble  Smith.) 


Between  the  hyaline  cartilage  of  which  the  foetal  femur  consists  and 
the  bony  tissue  forming  the  adult  femur,  two  intermediate  stages  exist — 
viz.,  calcified  cartilage,  and  embryonic  spongy  hone.  These  tissues, 
which  successively  occupy  the  place  of  the  foetal  cartilage,  are  in  suc- 
cession entirely  absorbed,  and  their  place  taken  by  true  bone. 


THE    STRUCTURE   OF   THE    ELKMiSNTABY    TISSUES.  53 

The  process  by  which  the  cartilaginous  is  transformed  into  the  bony 
femur  may  be  divided  for  the  sake  of  clearness  into  the  following  six 
stages : — 

Stage  I. — Vascularization  of  the  Cartilage. — Processes  from 
the  osteogenefcic  or  cellular  layer  of  the  perichondrium  containing  blood- 
vessels grow  into  the  substance  of  the  cartilage  much  as  ivy  insinuates 
itself  into  the  cracks  and  crevices  of  a  wall.  This  begins  at  the  "  centres 
of  ossification,"  from  which  the  blood-vessels  spread  chiefly  up  and 
down  the  shaft,  etc.  Thus  the  substance  of  the  cartilage,  which  previ- 
ously contained  no  vessels,  is  traversed  by  a  number  of  branched  anasto- 
mosing channels  formed  by  the  enlargement  and  coalescence  of  the 
spaces  in  which  the  cartilage-cells  lie,  and  containing  loops  of  blood- 
vessels (Fig.  59)  and  spheroidal  cells  which  will  become  osteoblasts. 

Stage  2. — Calcification  of  Cartilaginous  Matrix. — Lime  salts 
are  next  deposited  in  the  form  of  fine  granules  in  the  hyaline  matrix  of 
the  cartilage,  not  yet  vascularized,  which  thus  becomes  gradually  trans- 
formed into  a  number  of  calcified  trabecular  (Fig.  61,  5),  inclosing  al- 
veolar spaces  {primary  areolw)  which  contain  cartilage  cells.  By  the 
absorption  of  some  of  the  trabecular  larger  spaces  are  developed,  which 
contain  cartilage-cells  for  a  very  short  time  only,  their  places  being 
taken  by  the  so-called  osteogenetic  layer  of  the  perichondrium  (before 
referred  to  in  Stage  1)  which  constitutes  the  primary  marrow.  The 
cartilage-cells,  gradually  enlarging,  become  more  transparent  and  finally 
undergo  disintegration. 

Stage  3. — Substitution  of  Embryonic  Spongy  Bone  for  Carti- 
lage.— The  cells  of  the  primary  marrow  arrange  themselves  as  a  con- 
tinuous layer  like  epithelium  on  the  calcified  trabecular  and  deposit  a 
layer  of  bone,  which  ensheathes  the  calcified  trabecular:  these  calcified 
trabecular,  encased  in  their  sheaths  of  young  bone,  become  gradually  ab- 
sorbed, so  that  finally  we  have  trabecular  composed  entirely  of  spongy 
bone,  all  trace  of  the  original  calcified  cartilage  having  disappeared.  It 
ie  probable  that  the  large  multinucleated  giant-cells  termed  ''osteoclasts" 
by  Kolliker,  which  are  derived  from  the  osteoblasts  by  the  multiplication 
of  their  nuclei,  are  the  agents  by  which  the  absorption  of  calcified  carti- 
lage, and  subsequently  of  embryonic  spongy  bone,  is  carried  on  (Fig.  '2, 
g).  At  any  rate,  they  are  almost  always  found  wherever  absorption  is 
in  progress. 

Stages  2  and  3  are  precisely  similar  to  what  goes  on  in  the  growing 
shaft  of  a  bone  which  is  increasing  in  length  by  the  advance  of  the  pro- 
cess of  ossification  into  the  intermediary  cartilage  between  the  diaphysis 
and  epiphysis.  In  this  case  the  cartilage-cells  become  ilattened  and, 
multiplying  by  division,  are  grouped  into  regular  columns  at  right 
angles  to  the  plane  of  calcification,  while  the  process  of  calcification  ex- 
tends into  the  hyaline  matrix  between  them  (Figs.  59  and  60). 


54 


HANDBOOK    OF    PHYSIOLOGY. 


Stage  4. — Substitution  of  Periosteal  Bone  for  the  Primary- 
Embryonic  Spongy  Bone. — The  embryonic  spongy  bone,  formed  as 
above  described,  is  simply  a  temporary  tissue  occupying  the  place  of  the 
foetal  rod  of  cartilage,  once  representing  the  fenrar;  and  the  stages  1,  2, 
and  3  show  the  sucessive  changes  which  occur  at  the  centre  of  the  shaft. 
Periosteal  bone  is  now  deposited  in  successive  layers  beneath  the  perios- 
teum, i.  e.,  at  the  circumference  of  the  shaft,  exactly  as  described  in  the 
section  on  "ossification  in  membrane,"  and  thus  a  casing  of  periosteal 


Fig.  63.— Transverse  section  through  the  tibia  of  a  foetal  kitten,  semi-diagrammatic.  X  60.  P. 
Periosteum.  O,  osteogenetic  layer  of  the  periosteum  showing  the  osteoblasts  arranged  side  by- 
side,  represented  as  pear-shaped  black  dots  on  the  surface  of  the  newly  formed  bone.  B,  the  perios- 
teal bone  deposited  in  successive  layers  beneath  the  periosteum  and  ensheathin  »  E,  the  spongy  en- 
dochondral bone ;  represented  as  more  deeply  shaded.  Within  the  trabeculse  of  endochondral 
spongy  bone  are  seen  the  remains  of  the  calcified  cartilage  trabeculae  represented  as  dark  wavy 
lines.  C,  the  medulla  with  V,  V,  veins.  In  the  lower  half  of  the  figure  the  endochondral  spongy 
bone  has  been  completely  absorbed.    (Klein  and  Noble  Smith..) 


bone  is  formed  around  the  embryonic  endochondral  spongy  bone:  this 
casing  is  thickest  at  the  centre,  where  it  is  first  formed,  and  thins  out 
towards  each  end  of  the  shaft.  The  embryonic  spongy  bone  is  absorbed, 
its  trabecule  becoming  gradually  thinned  and  its  meshes  enlarging,  and 


THE    STRUCTURE    OF    THE    ELEMENTARY    TI88UK8.  55 

finally  coalescing   into  one   great  cavity — the    medullary  cavity  of  the 
shaft. 

Stage  5. — Absorption  of  the  Inner  Layers  of  the  Periosteal 
Bone. — The  absorption  of  the  endochondral  spongy  bone  is  now  com- 
plete, and  the  medullary  cavity  is  bounded  by  periosteal  bone;  the  inner 
layers  of  this  periosteal  bone  are  next  absorbed,  and  the  medullary  cavity 
is  thereby  enlarged,  while  the  deposition  of  bone  beneath  the  periosteum 
continues  as  before.  The  first-formed  periosteal  bone  is  spongy  in  char- 
acter. 

Stage  6. — Formation  of  Compact  Bone. — The  transformation  of 
spongy  periosteal  bone  into  compact  bone  is  effected  in  a  manner  exactly 
similar  to  that  which  has  been  described  in  connection  with  ossification 
in  membrane  (p.  49).  The  irregularities  in  the  walls  of  the  areola?  in 
the  spongy  bone  are  absorbed,  while  the  osteoblasts  which  line  them  are 
developed  in  concentric  layers,  each  layer  in  turn  becoming  ossified  till 
the  comparatively  large  space  in  the  centre  is  reduced  to  a  well-formed 
Haversian  canal  (Fig.  64).  When  once  formed,  bony  tissue  grows  to 
some  extent  interstitially,  as  is  evidenced  by  the  fact  that  the  lacunas  are 
rather  further  apart  in  fully-formed  than  in  young  bone. 

From  the  foregoing  description  of  the  development  of  bone,  it  will 
be  seen  that  the  common  terms  "ossification  in  cartilage"  and  "ossifi- 
cation in  membrane  "  are  apt  to  mislead,  since  they  seem  to  imply  two 
processes  radically  distinct.  The  process  of  ossification,  however,  is  in 
all  cases  one  and  the  same,  all  true  bony  tissue  being  formed  from  mem- 
brane (perichondrium  or  periosteum);  but  in  the  development  of  such  a 
bone  as  the  femur,  which  may  be  taken  as  the  type  of  so-called  "ossifi- 
cation in  cartilage/'  lime-salts  are  first  of  all  deposited  in  the  cartilage; 
this  calcified  cartilage,  however,  is  gradually  and  entirely  re  absorbed, 
being  ultimately  replaced  by  bone  formed  from  the  periosteum,  till  in 
the  adult  structure  nothing  but  true  bone  is  left.  Thus,  in  the  process 
of  "  ossification  in  cartilage,"  calcification  of  the  cartilaginous  matrix 
precedes  the  real  formation  of  bone.  We  must,  therefore,  clearly  dis- 
tinguish between  calcification  and  ossification.  The  former  is  simply 
the  infiltration  of  an  animal  tissue  with  lime-salts,  and  is,  therefore,  a 
change  of  chemical  composition  rather  than  of  structure;  while  ossifica- 
tion is  the  formation  of  true  bone — a  tissue  more  complex  and  more 
highly  organized  than  that  from  which  it  is  derived. 

Centres  of  Ossification. — In  all  bones  ossification  commences  at  one 
or  more  points,  termed  "  centres  of  ossification."  The  long  bones,  e.g., 
femur,  humerus,  etc.,  have  at  least  three  such  points — one  for  the  ossifi- 
cation of  the  shaft  or  diapkysis,  and  one  for  each  articular  extremity  or 
epiphysis.  Besides  these  three  primary  centres  which  are  a hv.ays  present 
in  long  bones,  various  secondary  centres  may  be  superadded  for  the  ossi- 
fication of  different  processes. 


56 


HANDBOOK    OF    PHYSIOLOGY. 


Growth  of  Bone.  — Bones  increase  in  length  by  the  advance  of  the 
process  of  ossification  into  the  cartilage  intermediate  between  the  dia- 
physis  and  epiphysis.  The  increase  in  length  indeed  is  due  entirely  to 
growth  at  the  two  ends  of  the  shaft.  This  is  proved  by  inserting  two 
pins  into  the  shaft  of  a  growing  bone;  after  some  time  their  distance 
apart  will  be  found  to  be  unaltered  though  the  bone  has  gradually  in- 
creased in  length,  the  growth  having  taken  place  beyond  and  not  between 

them.  If  now  one  pin  be  placed 
in  the  shaft,  and  the  other  in  the 
epiphysis,  of  a  growing  bone, 
their  distance  apart  will  increase 
as  the  bone  grows  in  length. 

Thus  it  is  that  if  the  epiphy- 
ses with  the  intermediate  car- 
tilage be  removed  from  a  young 
bone,  growth  in  length  is  no  long- 
er possible;  while  the  natural  ter- 
mination of  growth  of  a  bone  in 
length  takes  place  when  the  epi- 
physes become  united  in  bony 
continuity  with  the  shaft. 

Increase  in  thickness  in  the 
shaft  of  a  long  bone,  occurs  by 
the  deposition  of  successive  layers 
beneath  the  periosteum. 

If  a  thin  metal  plate  be  in- 
serted beneath  the  periosteum  of 
a  growing  bone,  it  will  soon  be 
covered  by  osseous  deposit,  but  if 
it  be  put  between  the  fibrous  and 
osteogenetic  layers,  it  will  never 
become   enveloped  in  bone,   for 


Fig.  64.— Transverse  section  of  femur  of  a 
human  embryo  about  eleven  weeks  old.  a,  rudi- 
mentary Haversian  canal  in  cross  section  ;  6,  in 
longitudinal  section;  c,  osteoblasts;  d,  newly  form- 
ed osseous  substance  of  a  lighter  color  ;  e,  that 
of  greater  age  ;  /,  lacunae  with  their  cells  ;  g,  a 
cell  still  united  to  an  osteoblast.     (Frey.) 


all  the  bone  is  formed  beneath  the  latter. 


Other  varieties  of  connective  tissue  may  become  ossified,  eg.,  the 
tendons  in  some  birds. 

Functions  of  Bones. — Bones  form  the  framework  of  the  body;  for 
this  they  are  fitted  by  their  hardness  and  solidity  together  with  their 
comparative  lightness;  they  serve  both  to  protect  internal  organs  in  the 
trunk  and  skull,  and  as  levers  worked  by  muscles  in  thelimbs;  notwith- 
standing their  hardness  they  possess  a  considerable  degree  of  elasticity, 
which  often  saves  them  from  fractures. 


CHAPTER   III. 

THE    BLOOD. 

The  blood  of  man,  as  indeed  of  the  great  majority  of  vertebrate 
animals,  is  a  more  or  less  viscid  red  fluid.  The  exact  shade  of  red  is 
variable,  for  whereas  that  taken  from  the  arteries,  from  the  left  side  of 
the  heart,  and  from  the  pulmonary  veins,  is  of  a  bright  scarlet  hue,  that 
obtained  from  the  systemic  veins,  from  the  right  side  of  the  heart,  and 
from  the  pulmonary  artery,  is  of  a  much  darker  color,  and  varies  from 
bluish-red  to  reddish-black.  At  first  sight,  the  red  color  appears  to  be- 
long to  the  whole  mass  of  blood,  but  on  further  examination  this  is 
found  not  to  be  the  case.  In  reality  blood  consists  of  an  almost  colorless 
fluid,  called  Plasma  or  Liquor  Sanguinis,  in  which  are  suspended 
numerous  minute  rounded  masses  of  protoplasm,  called  Blood  Corpuscles, 
which  are,  for  the  most  part,  colored,  and  it  is  to  their  presence  in  the 
fluid  that  the  red  color  of  the  blood  is  due. 

Even  when  examined  in  very  thin  layers  blood  is  opaque,  on  account 
of  the  different  refractive  powers  possessed  by  its  two  constituents,  viz., 
the  plasma  and  the  corpuscles.  On  treatment  with  chloroform  and  other 
reagents,  however,  it  becomes  transparent,  and  assumes  a  lake  color,  in 
consequence  of  the  coloring  matter  of  the  corpuscles  having  been  dis- 
charged into  the  plasma.  The  average  specific  gravity  of  blood  at  60°  F. 
(15°  C.)  is  1055,  the  extremes  consistent  with  health  being  1045-1062. 
The  reaction  of  blood  is  faintly  alkaline.  Its  temperature  varies  slightly, 
the  average  being  100°  F.  (37.8°  C).  The  blood  stream  is  warmed  by 
passing  through  the  muscles,  nerve  centres,  and  glands,  but  is  somewhat 
cooled  on  traversing  the  capillaries  of  the  skin.  Recently  drawn  blood 
has  a  distinct  odor,  which  in  many  cases  is  characteristic  of  the  animal 
from  which  it  has  been  taken.  It  may  be  further  developed  also  by 
adding  to  blood  a  mixture  of  equal  parts  of  sulphuric  acid  and  water. 

Quantity  of  the  Blood. — The  quantity  of  blood  in  any  animal 
under  normal  conditions  bears  a  pretty  constant  relation  to  the  body 
weight.  The  methods  employed  for  estimating  it  are  not  so  simple  ;i< 
might  at  first  sight  be  thought.  For  example,  it  would  not  be  possible 
to  get  any  accurate  information  on  the  point  from  the  amount  obtained 
by  rapidly  bleeding  an  animal  to  death,  for  then  an  indefinite  quantity 
would  remain  in  the  vessels,  as  wrlWis  in  the  tissues;  nor,  on  the  other 


58  HANDBOOK    OF    PHYSIOLOGY. 

hand,  would  it  be  possible  to  obtain  a  correct  estimate  by  less  rapid 
bleeding,  as,  since  life  would  be  more  prolonged,  time  would  be  allowed. 
for  the  passage  into  the  blood  of  lymph  from  the  lymphatic  vessels  and 
from  the  tissues.  In  the  former  case,  therefore,  we  should  underesti- 
mate, and  in  the  latter  over-estimate  the  total  amount  of  the  blood. 

Of  the  several  methods  which  have  been  employed,  the  most  accurate 
appears  to  be  the  following.  A  small  quantity  of  blood  is  taken  from  an 
animal  by  venesection;  it  is  defibrinated  and  measured,  and  used  to  make 
standard  solutions  of  blood.  The  animal  is  then  rapidly  bled  to  death, 
and  the  blood  which  escapes  is  collected.  The  blood  vessels  are  next 
washed  out  with  water  or  saline  solutions  until  the  washings  are  no  longer 
colored,  and  these  are  added  to  the  previously  withdrawn  blood;  lastly 
the  whole  animal  is  finely  minced  with  water  or  saline  solution.  The 
fluid  obtained  from  the  mincings  is  carefully  filtered,  and  added  to  the 
diluted  blood  previously  obtained,  and  the  whole  is  measured.  The  next 
step  in  the  process  is  the  comparison  of  the  color  of  the  diluted  blood 
with  that  of  standard  solutions  of  blood  and  water  of  a  known  strength, 
until  it  is  discovered  to  what  standard  solution  the  diluted  blood  corre- 
sponds. As  the  amount  of  blood  in  the  corresponding  standard  solution 
is  known,  as  well  as  the  total  quantity  of  diluted  blood  obtained  from 
the  animal,  it  is  easy  to  calculate  the  absolute  amount  of  blood  which 
the  latter  contained,  and  to  this  is  added  the  small  amount  which  was 
withdrawn  to  make  the  standard  solutions.  This  gives  the  total  amount 
of  blood  which  the  animal  contained.  It  is  contrasted  with  the  weight 
of  the  animal,  previously  known. 

The  result  of  many  experiments  shows  that  the  quantity  of  blood  in 
various  animals  averages  -fa  to  -fa  of  the  total  body  weight. 

An  estimate  of  the  quantity  in  man  which  corresponded  nearly  with 
this  proportion,  was  made  some  years  ago  from  the  following  data.  A 
criminal  was  weighed  before  and  after  decapitation;  the  difference  in  the 
weight  representing,  of  course,  the  quantity  of  blood  which  escaped. 
The  blood-vessels  of  the  head  and  trunk  were  then  washed  out  by  the 
injection  of  water,  until  the  fluid  which  escaped  had  only  a  pale  red  or 
straw  color.  This  fluid  was  then  also  weighed;  and  the  amount  of  blood 
which  it  represented  was  calculated  by  comparing  the  proportion  of  solid 
matter  contained  in  it  with  that  of  the  first  blood  which  escaped  on  de- 
capitation. Two  experiments  of  this  kind  gave  precisely  similar  results. 
(Weber  and  Lehmann.) 

It  should  be  remembered,  in  connection  with  these  estimations,  that 
the  quantity  of  the  blood  must  vary,  even  in  the  same  animal,  very  con- 
siderably with  the  amount  of  both  the  ingesta  and  egesta  of  the  period 
immediately  preceding  the  experiment;  and  it  has  been  found,  indeed, 
that  the  amount  of  blood  obtainable  from  the  body  of  a  fasting  animal 
rarely  exceeds  a  half  of  that  which  is  present  soon  after  a  full  meal. 

Coagulation  of  the  Blood. — One  of  the  most  characteristic  prop- 
erties which  the  blood  possesses  is  that  of  clotting  or  coagulating,  when 


THE   BLOOD. 


51* 


removed  from  the  body.  This  phenomenon  may  be  observed  under  the 
most  favorable  conditions  in  blood  which  has  been  drawn  into  an  open 
vessel.  In  about  two  or  three  minutes,  at  the  ordinary  temperature  of 
the  air,  the  surface  of  the  fluid  is  seen  to  become  semi-solid  or  jelly-like, 
and  this  change  takes  place,  in  a  minute  or  two  afterwards,  at  the  sides 
of  the  vessel  in  which  it  is  contained,  and  then  extends  throughout  the 
entire  mass. 

The  time  which  is  required  for  the  blood  to  become  solid  is  about 
eight  or  nine  minutes.  The  solid  mass  occupies  exactly  the  same  vol- 
ume as  the  previously  liquid  blood,  and  adheres  so  closely  to  the  sides 
of  the  containing  vessel  that  if  it  be  inverted  none  of  its  contents  escape. 
The  solid  mass  is  the  crassamentum  or  clot.  If  the  clot  be  watched  for 
a  few  minutes,  drops  of  a  light,  straw  colored  fluid,  the  serum,  may  be 
seen  to  make  their  appearance  on  the  surface  and,  as  they  become  more 


Fig.  65.— Reticulum  of  fibrin,  from  a  drop  of  human  blood,  after  treatment  with  rosanilin. 
(Ranvier. ) 


and  more  numerous,  to  run  together,  forming  a  complete  superficial 
stratum  above  the  solid  clot.  At  the  same  time  the  fluid  begins  to 
transude  at  the  sides  and  at  the  under  surface  of  the  clot,  which  in  the 
course  of  an  hour  or  two  floats  in  the  liquid.  The  first  drops  of  serum 
appear  on  the  surface  about  eleven  or  twelve  minutes  after  the  blood  has 
been  drawn;  and  the  fluid  continues  to  transude  for  from  thirty-six  to 
forty-eight  hours. 

The  clotting  of  blood  is  due  to  the  development  in  it  of  a  substance 
called  fibrin,  which  appears  as  a  meshwork  (Fig.  65)  of  fine  fibrils. 
This  meshwork  entangles  and  incloses  within  it  the  blood-corpuscles,  as 
clotting  takes  place  too  quickly  to  allow  them  to  sink  to  the  bottom  of 
the  plasma.  The  first  clot  formed,  therefore,  includes  the  whole  of  the 
constituents  of  the  blood  in  an  apparently  solid  mass,  but  soon  the  fibrin- 
ous meshwork  begins  to  contract,  and  the  serum  which  does  not  belong 


60  HANDBOOK    OF   PHYSIOLOGY. 

to  the  clot  is  squeezed  out.  When  the  whole  of  the  serum  has  trans- 
uded, the  clot  is  found  to  be  smaller,  but  firmer  and  harder,  as  it  is  now- 
made  up  of  fibrin  and  blood-corpuscles  only.  It  will  be  noticed  that 
coagulation  rearranges  the  constituents  of  the  blood  according  to  the 
following  scheme,  liquid  blood  being  made  up  of  plasma  and  blood-cor- 
puscles, and  clotted  blood  of  serum  and  clot. 

Liquid  Blood. 


I  | 

Plasma.  Corpuscles. 


Serum.  Fibrin. 


Clot. 


Clotted  Blood. 

Under  ordinary  circumstances  coagulation  occurs,  as  we  have  men- 
tioned above,  before  the  red  corpuscles  have  had  time  to  subside;  and 
thus  from  their  being  entangled  in  the  meshes  of  the  fibrin,  the  clot  is 
of  a  deep  red  color  throughout,  somewhat  darker,  it  may  be,  at  the  most 
dependent  part,  from  accumulation  of  red  corpuscles,  but  not  to  any 
very  marked  degree.  When,  however,  coagulation  is  delayed  from  any 
cause,  as  when  blood  is  kept  at  a  temperature  of  32°  F.  (0°  C),  or  when 
clotting  is  normally  a  slow  process,  as  in  the  case  of  horse's  blood,  or, 
lastly,  in  certain  diseased  conditions  of  the  blood  in  which  clotting  is 
naturally  delayed,  time  is  allowed  for  the  colored  corpuscles  to  sink  to 
the  bottom  of  the  fluid.  When  clotting  does  occur,  the  upper  layers  of 
the  blood,  being  free  of  colored  corpuscles  and  consisting  chiefly  of 
fibrin,  form  a  superficial  stratum  differing  in  appearance  from  the  rest 
of  the  clot,  in  that  it  is  of  a  grayish-yellow  color.  This  is  known  as  the 
'■'  huffy  coat." 

When  the  buffy  coat  has  been  produced  in  the  manner  just  described, 
it  commonly  contracts  more  than  the  rest  of  the  clot,  on  account  of  the 
absence  of  colored  corpuscles  from  its  meshes,  and  because  contraction  is 
less  interfered  with  by  adhesion  to  the  interior  of  the  containing  vessel 
in  the  vertical  than  the  horizontal  direction.  This  joroduces  a  cup-like 
appearance  of  the  buffy  coat,  and  the  clot  is  not  only  buffed  but  cupped 
on  the  surface.  The  buffed  and  cupped  appearance  of  the  clot  is  well 
marked  in  certain  states  of  the  system,  especially  in  inflammation,  where 
the  fibrin-forming  constituents  are  in  excess,  and  it  is  also  well  marked 
in  chlorosis  where  the  corpuscles  are  deficient  in  quantity. 

Formation  of  Fibrin. — That  the  clotting  of  blood,  is  due  to  the 
gradual  appearance  in  it  of  fibrin  is  universally  acknowledged.  It  may 
be   easily    demonstrated.     For   example,    if    recently   drawn   blood   be 


THE    BLOOD.  t)l 

whipped  with  a  bundle  of  twigs  which  presents  numerous  points  of  con- 
tact and  so,  as  we  shall  presently  see,  facilitates  coagulation,  the  fibrin 
may  be  withdrawn  from  the  blood  before  it  can  entangle  the  blood- 
corpuscles  within  its  meshes,  as  it  adheres  to  the  twigs  in  stringy  threads 
almost  free  from  corpuscles;  whereas  the  blood  from  which  the  fibrin 
has  been  withdrawn  no  longer  exhibits  the  power  of  spontaneous  coagu- 
lability. Although  these  facts  have  long  been  known,  the  closely  asso- 
ciated problem  as  to  the  exact  manner  in  which  fibrin  is  formed  is  still 
only  partially  solved.  It  will  be  most  convenient  to  treat  of  the  question 
step  by  step. 

In  the  first  place  it  appears  that  under  the  ordinary  conditions  of 
experiment,  fibrin  is  chiefly,  if  not  entirely  to  be  obtained  from  plasma  ; 
for  although  the  colorless  corpuscles  may  be  intimately  connected  with 
the  process,  as  will  be  shown  later  on,  yet  the  colored  corpuscles  do  not 
appear  to  take  an  active  part  in  it. 

This  statement  does  not  exclude  the  possibility  that  fibrin  may  be 
derived  from  the  colored  corpuscles  under  certain  conditions.  Indeed, 
this  is  more  than  probable,  as  experiments  have  shown  that  if  a  little 
defibrinated  blood  be  added  to  serum,  the  haemoglobin  leaves  the  stroma 
of  the  colored  corpuscles  of  the  blood,  and  a  substance  arises  from  it 
called  stroma-fibrin,  indistinguishable  from  ordinary  fibrin,  which  pro- 
duces clotting  of  the  serum. 

This  may  be  shown  by  experimenting  with  plasma  free  from  colored 
corpuscles. 

Plasma  maybe  procured  by  delaying  coagulation  in  blood  by  keeping 
it  at  a  low  temperature,  32°  F.  (0°  C),  until  the  colored  corpuscles, 
which  are  of  a  higher  specific  gravity  than  the  other  constituents  of 
blood,  have  had  time  to  sink  to  the  bottom  of  the  containing  vessel,  and 
to  leave  an  upper  stratum  of  colorless  plasma,  in  the  lower  layers  of 
which,  however,  are  many  colorless  corpuscles.  The  blood  of  the  horse 
is  specially  suited  for  the  purposes  of  this  experiment,  as  might  have 
been  expected  from  what  has  been  stated  as  to  its  naturally  slow  coagu- 
lating power.  A  portion  of  the  colorless  plasma,  if  decanted  into 
another  vessel  and  exposed  to  the  ordinary  temperature  of  the  air,  will 
be  seen  to  coagulate  just  as  though  it  were  the  entire  blood,  producing 
a  clot  similar  in  all  respects  to  blood  clot,  except  that  it  is  almost  color- 
less from  the  absence  of  red  corpuscles.  But  if  some  of  the  plasma  be 
diluted  with '  neutral  saline  solution,  coagulation  is  delayed,  and  the 
stages  of  the  gradual  formation  of  fibrin  may  be  more  conveniently 
watched.  The  viscidity  which  precedes  the  complete  coagulation  may 
be  actually  seen  to  be  due  to  fibrin  fibrils  developing  in  the  fluid — first 

1  Neutral  saline  solution  commonly  consists  of  a  .6  to  .75  solution  of  common  salt 
(sodium  chloride)  in  water. 


(>2  HANDBOOK    OF    PHVSIOLOGY. 

of  all  at  the  circumference  of  the  containing  vessels,  and  gradually  ex- 
tending throughout  the  mass. 

If  a  further  portion  of  plasma  be  whipped  with  a  bundle  of  twigs,  the 
fibrin  may  be  obtained  as  a  solid,  stringy  mass,  just  in  the  same  way  as 
from  the  entire  blood,  and  the  resulting  fluid  no  longer  retains  its  power 
of  spontaneous  coagulability. 

In  these  experiments,  it  is  not  necessary  that  the  plasma  shall  have 
been  obtained  by  the  process  of  cooling  above  described,  as  plasma 
obtained  in  any  other  way.  e.  g.,  by  allowing  blood  to  flow  direct  from 
the  vessels  of  an  animal  into  a  vessel  containing  a  third  or  a  fourth  of 
its  bulk  of  a  saturated  solution  of  a  neutral  salt  (preferably  of  magne- 
sium sulphate)  and  mixing  carefully,  will  answer  the  purpose  and,  just 
as  in  the  other  case,  the  colored  corpuscles  will  subside  leaving  the  clear 
superstratum  of  (salted)  plasma.  In  order  that  this  plasma  may  coagu- 
late, it  is  necessary  to  get  rid  of  the  salts  by  dialysis,  or  to  dilute  it  with 
several  times  its  bulk  of  water. 

Evidently,  therefore,  fibrin  is  as  a  rule  derived  from  the  plasma  of 
blood 

The  second  step  in  the  investigation  is  to  consider  from  what  part  of 
the  plasma  fibrin  is  formed,  and  to  that  we  shall  now  turn  our  attention. 

If  plasma  be  saturated  with  solid  magnesium  sulphate  or  sodium 
chloride,  a  white,  sticky  precipitate  called  plasmine  is  thrown  down, 
after  the  removal  of  which,  by  filtration,  the  plasma  will  not  spontane- 
ously coagulate.  Plasmine  is  soluble  in  dilute  neutral  saline  solutions, 
and  the  solution  of  it  speedily  coagulates,  producing  a  clot  composed  of 
fibrin.  Blood  plasma  therefore  contains  a  substance  without  which  it 
cannot  coagulate,  and  a  solution  of  which  is  spontaneously  coagulable. 
This  substance  is  very  soluble  in  dilute  saline  solutions,  and  is  not, 
therefore,  fibrin,  which  is  insoluble  in  these  fluids.  We  are,  therefore, 
led  to  the  belief  that  plasmine  ]3roduces  or  is  converted  into  fibrin,  when 
clotting  of  fluids  containing  it  takes  place. 

There  is  distinct  evidence  that  plasmine  is  a  compound  body  made 
up  of  two  or  more  substances,  and  that  it  is  not  mere  soluble  fibrin. 
This  view  is  based  upon  the  following  observations: — There  exists  in  all 
the  serous  cavities  of  the  body  in  health,  e.  g.,  the  pericardium,  the 
peritoneum,  and  the  pleura,  a  certain  small  amount  of  transparent  fluid, 
generally  of  a  pale  straw  color,  which  in  diseased  conditions  may  be 
greatly  increased.  It  somewhat  resembles  serum  in  appearance,  but  in 
reality  differs  from  it,  and  is  probably  closely  allied  to  plasma.  This 
serous  fluid  is  not,  as  a  rule,  spontaneously  coagulable,  but  maybe  made 
to  clot  on  the  addition  of  serum,  which  is  also  a  fluid  which  has  no  ten- 
dency of  itself  to  coagulate.  The  clot  produced  consists  of  fibrin,  and 
the  clotting  is  identical  with  the  clotting  of  plasma.  From  the  serous 
fluid  (that  from  the  inflamed  tunica  vaginalis  testis  or  hydrocele  fluid  is 


THE   BLOOD.  6?> 

mostly  used)  we  may  obtain,  by  saturating  it  with  solid  magnesium  sul- 
phate or  sodium  chloride,  a  white  viscid  substance  as  precipitate  which 
is  called  fibrinogen.  If  fibrinogen  be  separated  by  filtration,  it  can  be 
dissolved  in  water,  as  a  certain  amount  of  the  neutral  salt  used  in  pre- 
cipitating it  is  entangled  with  the  precipitate,  and  is  sufficient  to  pro- 
duce a  dilute  saline  solution  in  which  fibrinogen,  being  a  body  of  the 
globulin  class,  is  soluble.  The  solution  of  fibrinogen  has  no  tendency 
to  clot  of  itself.  The  same  body  may  also  be  obtained  as  a  viscid  pre- 
cipitate from  hydrocele  fluid  by  diluting  it  with  water,  and  passing  a 
brisk  stream  of  carbon  dioxide  gas  through  the  solution. 

Now  if  blood-serum  be  added  to  a  solution  of  fibrinogen,  obtained 
in  either  of  these  ways,  the  mixture  clots. 

On  the  other  hand,  from  blood-serum  may  be  obtained  another 
globulin  very  similar  in  properties  to  fibrinogen,  if  it  be  treated  in 
either  of  the  ways  by  which  fibrinogen  is  obtained  from  hydrocele  fluid; 
this  substance  is  called  paraglobulin,  and  it  may  be  separated  by  filtra- 
tion and  dissolved  in  a  dilute  saline  solution  in  a  manner  similar  to 
fibrinogen. 

If  the  solutions  of  fibrinogen  and  paraglobulin  be  mixed,  the  mix- 
ture cannot  be  distinguished  from  a  solution  of  plasmine,  and  in  a  great 
majority  of  cases  firmly  clots  like  that  solution,  whereas  a  mixture  of 
the  hydrocele  fluid  and  serum,  from  which  these  bodies  have  been  respec- 
tively taken,  no  longer  manifests  the  like  property. 

In  addition  to  this  evidence  of  the  compound  nature  of  plasmine,  it 
may  be  further  shown  that,  if  sufficient  care  be  taken,  both  fibrinogen 
and  paraglobulin  may  be  separately  obtained  from  plasma:  the  one,  fibri- 
nogen, as  a  flaky  precipitate,  by  adding  carefully  thirteen  per  cent  of 
crystalline  sodium  chloride  to  it;  and  the  other,  paraglobulin,  may  be 
precipitated,  after  the  removal  of  fibrinogen  by  filtration,  on  the  further 
addition  to  saturation  of  the  same  salt  or  of  magnesium  sulphate  to  the 
filtrate.  It  is  evident,  therefore,  that  both  these  substances  must  be 
thrown  down  together  when  plasma  is  at  once  saturated  with  sodium 
chloride  or  magnesium  sulphate,  and  that  the  mixture  of  the  two  cor- 
responds with  plasmine. 

So  far  it  has  been  shown  that  plasmine,  the  antecedent  of  fibrin,  to 
the  possession  of  which  blood  owes  its  power  of  coagulating,  is  not  a 
simple  body,  but  is  composed  of  at  least  two  factors— viz.,  fibrinogen 
and  paraglobulin;  there  is  reason  for  believing  that  yet  another  bod//  is 
■associated  with  them  in  plasmine  to  produce  coagulation;  this  is  what 
is  known  under  the  name  of  fibrin  ferment  (Schmidt). 

Let  us  now  consider  the  evidence  in  favor  of  this  view.  It  was  at  one 
time  thought  that  the  reason  why  hydrocele  fluid  coagulated,  when 
serum  was  added  to  it,  was  that  the  latter  fluid  supplied  the  paraglobu- 
lin which  the  former  lacked;  this,  however,  is  not  the  case,  as  hvdrocele 


64  HANDBOOK    OF    PHYSIOLOGY. 

fluid  does  not  lack  this  body,  and  moreover,  if  paraglobulin,  obtained 
from  serum  by  the  carbonic  acid  method,  be  added  to  it,  it  will  not 
coagulate,  neither  will  a  mixture  of  solutions  of  fibrinogen  and  para- 
globulin, obtained  in  the  same  way.  But  if  paraglobulin,  obtained  by 
the  saturation  method,  be  added  to  hydrocele  fluid,  it  will  clot,  as  will 
also,  as  we  have  seen  above,  a  mixed  solution  of  fibrinogen  and  parar 
globulin,  both  obtained  by  the  saturation  method.  From  this  it  is  evi- 
dent that  in  plasmine  there  is  something  more  than  the  two  bodies  above 
mentioned,  and  that  this  something  is  precipitated  with  the  paraglobu- 
lin by  the  saturation  method,  and  is  not  precipitated  by  the  carbonic 
acid  method. 

The  following  experiments  show  that  it  is  of  the  nature  of  a  ferment. 
If  defibrinated  blood  or  serum  be  kept  in  a  stoppered  bottle  with  its  own 
bulk  of  alcohol  for  some  weeks,  all  the  proteid  matter  is  precipitated  in 
a  coagulated  form;  if  the  precipitate  be  then  removed  by  filtration, 
dried  over  sulphuric  acid,  finely  powdered,  and  then  suspended  in  water, 
a  watery  extract  may  be  obtained  by  further  filtration,  containing  ex- 
tremely little,  if  any,  proteid  matter.  Yet  a  little  of  this  watery  ex- 
tract will  produce  coagulation  in  fluids,  e.g.,  hydrocele  fluid  or  diluted 
plasma,  which  are  not  spontaneously  coagulable,  or  which  coagulate 
slowly  and  with  difficulty.  It  will  also  cause  a  mixture  of  fibrinogen 
and  paraglobulin,  both  obtained  by  the  carbonic  acid  method,  to  clot. 
The  watery  extract  appears  to  contain  the  body  which  is  precipitated 
with  the  paraglobulin  by  the  saturation  method.  Its  active  properties 
are  entirely  destroyed  by  boiling.  The  amount  of  the  extract  added 
does  not  influence  the  amount  of  the  clot  formed,  but  only  the  rapidity 
of  clotting,  aud  moreover  the  active  substance  contained  in  the  extract 
evidently  does  not  form  part  of  the  clot,  as  it  may  be  obtained  from  the 
serum  after  blood  has  clotted.  So  that  the  third  factor,  which  is  contained 
in  the  aqueous  extract  of  blood,  appears  to  belong  to  that  class  of 
bodies  which  promote  the  union  of,  or  cause  changes  in,  other  bodies, 
without  themselves  entering  into  union  or  undergoing  change,  i.e..  fer- 
ments. The  third  substance  has,  therefore,  received  the  name  fibrin 
ferment.  This  ferment  is  developed  in  blood  soon  after  it  has  been  shed, 
and  its  amount  appears  to  increase  for  some  little  time  afterwards 
(p.  65). 

So  far  we  have  seen  that  plasmine  is  a  body  composed  of  three  sub- 
stances, viz.,  fibrinogen,  paraglobulin,  and  fibrin  ferment.  The  next  ques- 
tion which  presents  itself  is,  are  these  three  bodies  actively  concerned  in  the 
formation  offi:/rin?  Here  we  come  to  a  point  about  which  two  distinct 
opinions  prevail,  aud  which  it  will  be  necessary  to  mention. 

On  the  one  hand  Schmidt  holds  that  fibrin  is  produced  by  the  inter- 
action of  the  two  proteid  bodies,  viz  .  fibrinogen  and  paraglobulin, 
brought  about  by  the  presence  of  a  special  fibrin  ferment.     Also,  that 


THE    BLOOD.  0"> 

when  coagulation  does  not  occur  in  serum,  which  contains  paraglohulin 
and  the  Gbrin  ferment,  the  non-coagulation  is  accounted  for  by  lack  of 
fibrinogen,  and  that  when  it  does  not  occur  in  fluids  which  contain 
fibrinogen,  it  is  due  to  the  absence  of  paraglobulin,  or  of  the  ferment,  or 
of  both.  It  will  be  seen  that,  according  to  this  view,  paraglobulin  has 
a,  very  important  fibrino-plastic  property. 

On  the  other  hand  Hammersten  holds  that  paraglobulin  is  not  an 
essential  in  coagulation,  or  at  any  rate  does  not  take  an  active  part  in 
the  process.  He  believes  that  paraglobulin  possesses  the  property  in 
common  with  many  other  bodies  of  combining  with — or  decomposing, 
a,nd  so  rendering  inert — certain  substances  which  have  the  power  of  pre- 
venting the  formation  or  precipitation  of  fibrin,  this  power  of  preventing 
coagulation  being  well  known  to  belong  to  the  free  alkalies,  to  the  alka- 
line carbonates,  and  to  certain  salts  ;  and  he  looks  upon  fibrin  as  formed 
from  fibrinogen,  which  is  either  (1)  decomposed  into  that  substance  with 
the  production  of  some  other  substances  ;  or  (2)  bodily  converted  into  it 
under  the  action  of  a  ferment,  which  is  frequently  precipitated  with 
paraglobulin. 

Hammersten's  view  as  to  the  formation  of  fibrin  from  fibrinogen  by 
the  action  of  a  second  body,  possibly  of  the  ferment  class,  is  now  very 
generally  held.  The  presence  of  a  certain  but  small  amount  of  salts, 
especially  of  sodium  chloride,  is  necessary  for  coagulation,  and  without 
it,  clotting  cannot  take  place. 

Sources  of  the  Fibrin  Generators. — It  has  been  previously  re- 
marked that  the  colorless  corpuscles  which  are  always  present  in  smaller 
or  greater  numbers  in  the  plasma,  even  when  this  has  been  freed  from 
colored  corpuscles,  have  an  important  share  in  the  production  of  the 
clot.  The  proofs  of  this  may  be  briefly  summarized  as  follows  : — (1) 
That  all  strongly  coagulable  fluids  contain  colorless  corpuscles  almost  in 
direct  proportion  to  their  coagulability  ;  (2)  That  clots  formed  on  for- 
eign bodies,  such  as  needles  projecting  into  the  interior  or  lumen  of 
living  blood-vessels,  are  preceded  by  an  aggregation  of  colorless  corpus- 
cles ;  (3)  That  plasma  in  which  the  colorless  corpuscles  happen  to  be 
scanty,  clots  feebly ;  (4)  That  if  horse's  blood  be  kept  in  the  cold,  so 
that  the  corpuscles  subside,  it  will  be  found  that  the  lowest  stratum, 
containing  chiefly  colored  corpuscles,  will,  if  removed,  clot  feebly,  as  it 
contains  little  of  the  fibrin  factors  ;  whereas  the  colorless  plasma,  es- 
pecially the  lower  layers  of  it  in  which  the  colorless  corpuscles  are  most 
numerous,  will  clot  well,  but  if  filtered  in  the  cold  will  not  clot  so  well, 
indicating  that  when  filtered  nearly  free  from  colorless  corpuscles  even 
the  plasma  does  not  contain  sufficient  of  all  the  fibrin  factors  to  produce 
thorough  coagulation  ;  (5)  In  a  drop  of  coagulating  blood,  observed 
under  the  microscope,  the  fibrin  fibrils  are  seen  to  start  from  the  color- 
less corpuscles. 
5 


66  HANDBOOK    OF    PHYSIOLOGY. 

Although  the  intimate  connection  of  the  colorless  corpuscles  with  the 
process  of  coagulation  seems  indubitable,  for  the  reasons  just  given,  the 
exact  share  which  they  have  in  contributing  the  various  fibrin  factors 
still  remains  uncertain.  It  is  generally  believed  that  the  fibrin-ferment 
at  any  rate  is  contributed  by  them,  inasmuch  as  the  quantity  of  this 
substance  obtainable  from  plasma  bears  a  direct  relation  to  the  numbers 
of  colorless  corpuscles  which  the  plasma  contains.  Many  believe  that 
the  fibrinogen  too  is  wholly  or  in  part  derived  from  them,  and  also  that 
they  are  the  usual  source  of  the  paraglobul in  present  in  plasma.  Accord- 
ing to  this  view  all  the  fibrin  factors  are  derived  from  the  disintegration 
of  the  colorless  corpuscles.  We  have  seen  that  the  colored  corpuscles 
may  also  under  certain  circumstances  take  a  share  in  producing  the 
fibrin  generators. 

Conditions  affecting  Coagulation. — The  coagulation  of  the  blood 
is  hastened  by  the  following  means  : — 

1.  Moderate  warmth—  from  100°  to  120°  F.  (37.8-49°  C). 

2.  Rest  is  favorable  to  the  coagulation  of  blood.  Blood,  of  which 
the  whole  mass  is  kept  in  uniform  motion,  as  when  a  closed  vessel  com- 
pletely filled  with  it  is  constantly  moved,  coagulates  very  slowly  and  im- 
perfectly. 

3.  Contact  icith  foreign  matter,  and  especially  multiplication  of  the 
points  of  contact.  Thus,  as  before  mentioned,  fibrin  may  be  quickly  ob- 
tained from  liquid  blood  by  stirring  it  with  a  bundle  of  small  twigs  ;  and 
even  in  the  living  body  the  blood  will  coagulate  upon  rough  bodies  pro- 
jecting into  the  vessels. 

4.  The  free  access  of  air. — Coagulation  is  quicker  in  shallow  than  in 
tall  and  narrow  vessels. 

5.  The  addition  of  less  than  twice  the  bulk  of  water. 

The  blood  last  drawn  is  said,  from  being  more  watery,  to  coagulate 
more  quickly  than  the  first. 

The  coagulation  of  the  blood  is  retarded,  suspended,  or  prevented 
by  the  following  means  : 

1.  Cold  retards  coagulation  •  and  so  long  as  blood  is  kept  at  a  tem- 
perature, 32°  F.  (0°  C),  it  will  not  coagulate  at  all.  Freezing  the 
blood,  of  course,  prevents  its  coagulation  ;  yet  it  will  coagulate,  though 
not  firmly,  if  thawed  after  being  frozen  ;  and  it  will  do  so,  even  after  it 
has  been  frozen  for  several  months.  A  higher  temperature  than  120°  F. 
(49°  C.)  retards  coagulation,  by  coagulating  the  albumen  of  the  serum, 
and  a  still  higher  one  above  56°  C.  prevents  it  altogether. 

2.  The  addition  of  water  in  greater  proportion  than  tioice  the  bulk 
of  the  blood,  also  the  addition  of  syrup,  glycerin,  and  other  viscid  sub- 
stances. 

3.  Contact  with  living  tissues,  and  especially  with  the  interior  of  a 
living  blood-vessel. 


tiii:  blood.  67 

4.  The  addition  of  neutral  salts  in  the  proportion  of  2  or  3  per  cent 
and  upwards.  When  added  in  large  proportion  most  of  these  saline 
substances  prevent  coagulation  altogether.  Coagulation,  however,  ensues 
on  dilution  with  water.  The  time  during  which  blood  can  be  thus  pre- 
served in  a  liquid  state  and  coagulated  by  the  addition  of  water,  is  quite 
mdefinite. 

5.  Imperfect  aeration — as  in  the  blood  of  those  who  die  by  asphyxia. 

6.  In  inflammatory  states  of  the  system  the  blood  coagulates  more 
slowly  although  more  firmly. 

7.  Coagulation  is  retarded  by  exclusion  of  the  blood  from  the  air,  as  by 
pouring  oil  on  the  surface,  etc.  In  vacuo,  the  blood  coagulates  quickly  ; 
but  Lister  thinks  that  the  rapidity  of  the  process  is  due  to  the  bubbling 
which  ensues  from  the  escape  of  gas,  and  to  the  blood  being  thus  brought 
more  freely  into  contact  with  the  containing  vessel.  Receiving  blood 
into  a  vessel,  well  smeared  inside  with  oil,  fat,  or  vaseline,  is  said  also  to 
retard  or  prevent  coagulation. 

8.  The  coagulation  of  the  blood  is  prevented  altogether  by  the  addi- 
tion of  strong  acids  and  caustic  alkalies. 

9.  It  has  been  believed,  and  chiefly  on  the  authority  of  Hunter,  that 
after  certain  modes  of  death  the  blood  does  not  coagulate  ;  he  enumerates 
the  death  by  lightning,  over-exertion  (as  in  animals  hunted  to  death), 
blows  on  the  stomach,  fits  of  anger.  He  says,  "  I  have  seen  instances  of 
them  all."  Doubtless  he  had  done  so  ;  but  the  results  of  such  events  are 
not  constant.  The  blood  has  been  often  observed  coagulated  in  the 
bodies  of  animals  killed  by  lightning  or  an  electric  shock  ;  and  Gulliver 
has  published  instances  in  which  he  found  clots  in  the  hearts  of  hares 
and  stags  hunted  to  death,  and  of  cocks  killed  in  fightiug. 

10.  The  injection  of  peptones,  or  of  various  digestive  ferments,  e.  g., 
trypsin  or  pepsin,  into  the  vessels  of  an  animal  appears  to  prevent  or 
stay  coagulation  of  its  blood  if  it  be  killed  soon  after.  The  secretion 
of  the  mouth  of  the  leech,  and  possibly  the  blood  squeezed  out  of  its  body 
Avhen  full,  also  prevents  the  clotting  if  added  to  blood. 

Cause  of  the  fluidity  of  the  blood  within  the  living  body.— 

Very  closely  connected  with  the  problem  of  the  coagulation  of  the  blood 
is  the  question — why  does  the  blood  remain  liquid  within  the  living  bodv? 
We  have  certain  pathological  and  experimental  facts,  apparently  opposed 
to  one  another,  which  bear  upon  it,  and  these  may  be,  for  the  sake  of 
clearness,  classed  under  two  heads: — 

(1)  Blood  will  coagulate  within  the  living  body  under  certain  condi- 
tions—for  example,  on  ligaturing  an  artery,  whereby  the  inner  and 
middle  coats  are  generally  ruptured,  a  clot  will  form  within  it,  or  by 
passing  a  needle  through  the  coats  of  the  vessel  into  the  blood  stream  a 
clot  will  gradually  form  upon  it.  Other  foreign  bodies,  e.g.,  wire,  thread, 
etc.,  produce  the  same  effoct.  It  is  a  well-known  fact  that  small  clots 
are  apt  to  form  upon  the  rougheued  edges  of  the  valves  of  the  heart  when 


68  HANDBOOK   OF   PHYSIOLOGY. 

the  roughness  has  been  produced  by  inflammation,  as  in  endocarditis, 
and  it  is  also  equally  true  that  aneurysms  of  arteries  are  sometimes  spon- 
taneously cured  by  the  deposition  within  them,  layer  by  layer,  of  fibrin 
from  the  blood  stream,  which  natural  cure  it  is  the  aim  of  the  physician 
or  surgeon  to  imitate. 

(2)  Blood  will  remain  liquid  under  certain  conditions  outside  the 
body,  without  the  addition  of  any  reagent,  even  if  exposed  to  the  air  at 
the  ordinary  temperature.  It  is  well  known  that  blood  remains  fluid  in 
the  body  for  some  time  after  death,  and  it  is  only  after  rigor  mortis  has 
occurred  that  the  blood  is  found  clotted.  It  has  been  demonstrated  by 
Hewson,  and  also  by  Lister,  that  if  a  large  vein  in  the  horse  or  similar 
animal  be  ligatured  in  two  places  some  inches  apart,  and  after  sometime 
be  opened,  the  blood  contained  within  it  will  be  found  fluid,  and  that 
coagulation  will  occur  only  after  a  considerable  time.  But  this  is  not 
due  to  occlusion  from  the  air  simply.  Lister  further  showed  that  if  the 
vein  with  the  blood  contained  within  it  be  removed  from  the  body,  and 
then  be  carefully  opened,  the  blood  might  be  poured  from  the  vein  into 
another  similarly  prepared,  as  from  one  test-tube  into  another,  thereby 
suffering  free  exposure  to  the  air,  without  coagulation  occurring  as  long 
as  the  vessels  retain  their  vitality.  If  the  endothelial  lining  of  the  vein, 
however,  be  injured,  the  blood  will  not  remain  liquid.  Again,  blood 
will  remain  liquid  for  days  in  the  heart  of  a  turtle,  which  continues  to 
beat  for  a  very  long  time  after  removal  from  the  body. 

Any  theory  which  aims  at  explaining  the  normal  fluidity  of  the  blood 
within  the  living  body  must  reconcile  the  above  apparently  contradictory 
facts,  and  must  at  the  same  time  be  made  to  include  all  other  known 
facts  concerning  coagulation.  We  may  therefore  dismiss  as  insufficient 
the  following: — that  coagulation  is  due  to  exposure  to  the  air  or  oxygen; 
that  it  is  due  to  the  cessation  of  the  circulatory  movement;  that  it  is  due 
to  evolution  of  various  gases,  or  to  the  loss  of  heat. 

Two  theories,  those  of  Lister  and  Briicke,  remain.  The  former  sup- 
poses that  the  blood  has  no  natural  tendency  to  clot,  but  that  its  coagu- 
lation out  of  the  body  is  due  to  the  action  of  foreign  matter  with  which 
it  happens  to  be  brought  into  contact,  and  in  the  body  to  conditions  of 
the  tissues  which  cause  them  to  act  towards  it  like  foreign  matter.  The 
latter,  on  the  other  hand,  supposes  that  there  is  a  natural  tendency  on 
the  part  of  the  blood  to  clot,  but  that  this  is  restrained  in  the  living 
body  by  some  inhibitory  power  resident  in  the  walls  of  the  containing 
vessels. 

The  blood  must  contain  all  the  substances  from  which  fibrin  is  formed, 
and  the  re-arrangement  of  these  substances  must  occur  very  quickly 
whenever  the  blood  is  shed,  and  so  it  is  somewhat  difficult  to  prevent 
coagulation.  It  seems  more  reasonable  to  hold,  therefore,  that  the  blood 
has  a  strong  tendency  to  clot,  rather  than  that  it  has  no  special  tendency 
thereto. 

But  it  has  been  recently  suggested  that  the  reason  why  blood  does  not 
coagulate  in  the  living  vessels,  is  that  the  factors  which  are  necessary  for 
the  formation  of  fibrin  are  not  in  the  exact  state  required  for  its  produc- 
tion, and  that  at  any  rate  the  fibrin  ferment  is  not  formed  or  is  not  free 
in  the  living  blood,  but  that  it  is  produced  (or  set  free)  at  the  moment 


THE    BLOOD.  69 

of  coagulation  b\r  the  disintegration  of  the  colorless  (and  possibly  of  the 
colored)  corpuscles.  This  supposition  is  certainly  plausible,  and  if  it  be 
a  true  one,  it  must  be  assumed  either  that  the  liYing  blood-vessels  exert 
a  restraining  influence  upon  the  disintegration  of  the  corpuscles  in  suffi- 
cient numbers  to  form  a  clot,  or  that  they  render  inert  any  small  amount 
of  fibrin  ferment  which  may  have  been  set  free  by  the  disintegration  of 
a  few  corpuscles;  as  it  is  certain,  firstly,  that  corpuscles  of  all  kinds  must 
from  time  to  time  disintegrate  in  the  blood  without  causing  it  to  clot; 
and,  secondly,  that  shed  and  defibrinated  blood  which  contains  blood 
corpuscles,  broken  down  and  disintegrated,  will  not,  when  injected  into 
the  vessels  of  an  animal,  under  ordinary  conditions,  produce  clotting. 
There  must  be  a  distinct  difference,  therefore,  if  only  in  amount,  between 
the  normal  disintegration  of  a  few  colorless  corpuscles  in  the  living  un- 
injured blood-vessels  and  the  abnormal  disintegration  of  a  large  number 
which  occurs  whenever  the  blood  is  shed  without  suitable  precaution,  or 
when  coagulation  is  unrestrained  by  the  neighborhood  of  the  living  un- 
injured blood-vessels. 

The  explanation  of  the  clotting  of  blood  which  has  been  given  in  the 
preceding  pages  and  which  depends  chiefly  upon  the  researches  of  Alex. 
Schmidt  and  Hammersten,  supposes  that  it  is  one  of  the  fermentative 
actions,  so  many  of  which  are  believed  to  go  on  in  the  living  body.  Wool- 
dridge  ably  contests  this  view  of  the  process.  His  laborious  researches 
have  led  him  to  the  belief  that  coagulation  of  the  blood  is  a  vital  pro- 
cess, or  rather  that  it  is  the  last  act  of  vitality  displayed  by  blood  plasma, 
which  he  considers  to  be  during  life,  living  protoplasm.  Some  of  the 
results  of  his  experiments  may  with  advantage  be  here  mentioned,  as 
they  correct  and  amplify  the  information  as  to  blood-clotting  which  has 
been  hitherto  given  and  received.  Firstly,  he  has  shown  that  plasma 
itself  contains  everything  that  is  necessary  for  coagulation.  Peptone 
plasma  obtained  by  injecting  a  solution  of  peptone  into  the  veins  of  an 
animal  and  bleeding  it  immediately  afterwards  was  experimented  with. 
The  whole  of  the  corpuscular  elements  were  removed  by  repeated  treat- 
ment with  a  centrifugal  machine.  The  plasma  thus  obtained  was  shown 
to  clot  by  the  use  of  some  simple  mechanical  means,  e.g.,  filtering 
through  a  clay  cell,  or  through  filter  paper,  or  on  neutralization  with 
acetic  acid,  or  carbonic  acid,  or  by  dilution  with  water  or  saline  solution. 
Thus  it  would  appear  that  if  the  colorless  blood-corpuscles  aid  coagula- 
tion, their  influence  is  only  secondary. 

Secondly,  he  has  shown  that  the  important  precursor  of  clotting  in 
this  peptone  plasma  may  be  separated  from  it,  as  a  precipitate,  if  the 
plasma  be  kept  in  ice  for  some  time,  and  that  after  its  removal  the 
plasma  contains  only  a  little  fibrinogen  capable  of  clotting  by  the  action 
of  fibrin  ferment.  If  the  plasma  be  diluted  with  water  or  slightlv  acid- 
ulated, however,  the  fibrin  ferment  is  able  to  produce  a  complete 
clotting. 

In  peptone  plasma,  "Wooldridge  states  that  three  coagulable  bodies 
exist,  which  he  calls  A,  B,  and  C  fibrinogen,  and  which  are  closely 
allied  to  one  another.  C-fibrinogen  is  identical  with  the  body  which 
has  been  hitherto  described  as  fibrinogen,  is  present  in  very  small  amount, 


70  HANDBOOK   OF   PHYSIOLOGY. 

and  clots  on  addition  of  fibrin  ferment.  The  coagulable  matter  present 
in  greatest  amount  is  B-fibrinogen,  which  clots  on  addition  of  lecithin, 
or  of  lymph  corpuscles,  but  not  on  the  addition  of  fibrin  ferment;  A- 
fibrinogenis  separated  from  plasma  by  cooling,  in  minute  regular  rounded 
granules,  from  which  rounded  distinctly  biconcave  discs  arise,  if  watched 
under  the  microscope,  quite  indistinguishable  from  colored  blood-cor- 
pus :les;  it  is  not  coagulated  by  fibrin  ferment.  Finally,  he  considers 
that  when  blood  plasma  dies,  an  action  takes  place  between  A-  and  B- 
fibrinogen  which  are  both  compounds  of  proteid  and  lecithin.  The  es- 
seutial  of  this  action  is  a  loss  of  lecithin  on  the  part  of  the  former  and 
a  gain  of  lecithin  on  the  part  of  the  latter,  with  the  result  of  the  pro- 
duction of  fibrin,  a  third  proteid-lecithin  compound,  and  the  setting 
free  of  other  substances  contained  in  the  serum,  including  fibrin  fer- 
ment. Thus,  fibrin  ferment,  a  body  which  can  convert  C-fibrinogen 
into  fibrin,  is  not  present  in  living  plasma,  but  is  a  result  of  its  disor- 
ganization or  death.  As  the  fibrinogen  which  can  be  clotted  by  the  fer- 
ment is  only  present  in  minimal  amounts  in  living  plasma,  injection  of 
a  solution  of  fibrin  ferment  or  of  shed  blood  does  not  produce  intra- 
vascular clotting,  whereas  injection  of  lymph  corpuscles  from  lymphatic 
glands  or  of  lecithin,  either  of  which  will  produce  clotting  of  the  other 
fibrinogens  which  form  the  bulk  of  the  coagulable  matter  in  living 
blood,  leads  to  extensive  intra-vascular  clotting. 

The  Blood  Corpuscles. 

There  are  two  principal  forms  of  corpuscles,  the  red  and  the  white, 
or,  as  they  are  now  frequently  named,  the  colored  and  the  colorless. 
In  the  moist  state,  the  red  corpuscles  form  about  45  percent  by  weight  of 
the  whole  mass  of  the  blood.  The  proportion  of  colorless  corpuscles  is 
only  as  1  to  500  or  600  of  the  colored. 

Red  or  Colored  Corpuscles. — Human  red  blood-corpuscles  are 
circular,  biconcave  discs  with  rounded  edges,  from  -g-oVo  to  joVo"  inch  in 
diameter,  and  t?^Tq-  inch  in  thickness,  becoming  flat  or  convex  on  addi- 
tion of  water.  When  viewed  singly,  they  appear  of  a  pale  yellowish 
tinge;  the  deep  red  color  which  they  give  to  the  blood  being  observable 
in  them  only  when  they  are  seen  en  masse.  They  are  composed  of  a 
colorless,  structureless,  and  transparent  filmy  framework  or  stroma,  in- 
filtrated in  all  parts  by  a  red  coloring  matter  termed  hmnoglobin.  The 
stroma  is  tough  and  elastic,  so  that,  as  the  corpuscles  circulate,  they 
admit  of  elongation  and  other  changes  of  form,  in  adaptation  to  the  ves- 
sels, yet  recover  their  natural  shape  as  soon  as  they  escape  from  com- 
pression. 

The  term  cell,  in  the  sense  of  a  bag  or  sac,  although  sometimes  ap- 
plied, is  inapplicable  to  the  red  blood-corpuscle;  and  it  must  be  consid- 
ered, if  not  solid  throughout,  yet  as  having  no  such  variety  of  consis- 
tence in  different  parts  as  to  justify  the  notion  of  its  being  a  membranous 
sac  with  fluid  contents.  The  stroma  exists  in  all  parts  of  its  substance, 
and  the  coloring  matter  uniformly  pervades  this,  and  is  not  merely  sur- 


THE    BLOOD. 


71 


rounded  by   and  mechanically    inclosed  within  the  outer  wall  of   the 
corpuscle. 

The  red  corpuscles  have  no  nuclei,  although  in  their  usual  state  the 
unequal  refraction  of  transmitted  light  gives  the  appearance  of  a  central 
spot,  brighter  or  darker  than  the  border,  according  as  it  is  viewed  in  or 
out  of  focus.     Their  specific  gravity  is  about  1088. 

Varieties. — The  red  corpuscles  are  not  all  alike,  some  being  rather 
larger,  paler,  and  less  regular  than  the  majority,  and  sometimes  flat  or 
slightly  convex,  with  a  shining  part  apparent  like  a  nucleolus.  In 
almost  every  specimen  of  blood  may  be  also  observed  a  certain  number 
of  corpuscles  smaller  than  the  rest.  They  are  termed  microcyfes,  and 
are  probably  immature  corpuscles. 

It  is  necessary  to  take  notice  that  much  importance  is  attached  to 
one  form  of  these  smaller  corpuscles 
named  blood  plates  by  Bizzozero.  They 
are  small,  more  or  less  rounded  or 
slightly  oval  granules,  slightly  if  at  all 
colored,  and  about  one-third  the  size 
of  ordinary  colored  corpuscles.  From 
them  it  is  supposed  the  fibrin  ferment 
is  specially  derived.  Some  go  so  far  as 
t»  say  that  they  are  practically  broken 
up  into  it  alone.  They  rapidly  under- 
go change  in  blood  after  it  has  been 
drawn.  They  may  form  masses  by  co- 
alescing. 

A    peculiar    property    of    the    red 
corpuscles,    which    is    exaggerated    in 

inflammatory  blood,  may  be  here  again  noticed,  i.  e.,  their  great  ten- 
dency to  adhere  together  in  rolls  or  columns,  like  piles  of  coins.  These 
rolls  quickly  fasten  together  by  their  ends,  and  cluster;  so  that,  when 
the  blood  is  spread  out  thinly  on  a  glass,  they  form  a  kind  of  irregular 
network,  with  crowds  of  corpuscles  at  the  several  points  corresponding 
with  the  knots  of  the  net  (Fig.  6*6).  Hence  the  clot  formed  in  such  a 
thin  layer  of  blood  looks  mottled  with  blotches  of  pink  upon  a  white 
ground,  and  in  a  larger  quantity  of  such  blood  help,  by  the  consequent 
rapid  subsidence  of  the  corpuscles,  in  the  formation  of  the  buffy  coat 
already  referred  to. 

Action  of  Reagents.— Considerable  light  has  been  thrown  on  the 
physical  and  chemical  constitution  of  red  blood-cells  by  studying  the 
effects  produced  by  mechanical  means  and  by  various  reagents;  the  fol- 
lowing is  a  brief  summary  of  these  reactions: 

Pressure. — If  the  red  blood-cells  of  a  frog  or  man  are  gentlv 
squeezed,  they  exhibit  a  wrinkling  of  the  surface,  which  clearly  indi- 
cates that  there  is  a  superficial  pellicle  partly  differentiated   Erom  the 


Fig.  C6.— Red   corpuscles  in  rouleaux. 
At  a,  a,  are  two  white  corpuscles. 


72 


HANDBOOK    OF    PHYSIOLOGY, 


softer  mass  within;  again,  if  a  needle  be  rapidly  drawn  across  a  drop  of 
blood,  several  corpuscles  will  be  found  cut  in  two,  but  this  is  not  accom- 
panied by  any  escape  of  cell  contents;  the  two  halves,  on  the  contrary, 
assume  a  rounded  form,  proving  clearly  that  the  corpuscles  are  not  mere 
membranous  sacs  with  fluid  contents  like  fat-cells. 

Fluids,     i.    Water. — When  water  is  added  gradually  to  frog's  blood, 
the  oval  disc-shaped  corpuscles  become  spherical,  and  gradually  discharge 
their  haemoglobin,  a  pale,  transparent  stroma  being  left  behind;  human 
red  blood-cells  change  from  a  discoidal  to  a  spheroidal  form,  and  dis- 
charge their  cell-contents,  becoming  quite  transparent 
and  all  but  invisible. 
W  &  ii.   Saline  solution  (dilute)  produces  no  appreciable 

<%£§  effect  on  the  red  blood-cells  of  the  frog.     In  the  red 

blood-cells  of  man  the  discoid  shape  is  exchanged  for  a 
fig.  67.  spherical  one,  with  spinous  projections,   like  a  horse- 

chestnut   (Fig.    67).     Their  orginal   forms  can  be  at 
once  restored  by  the  use  of  carbonic  acid. 

iii.  Acetic  acid  (dilute)  causes  the  nucleus  of  the  red  blood-cells  in 
the  frog  to  become  more  clearly  denned;  if  the  action  is  prolonged,  the 


Fiq.  68.— The  above  illustration  is  somewhat  altered  from  a  drawing  by  Gulliver,  in  the  Proceed 
Znol.  Society,  and  exhibits  the  typical  characters  of  the  red  blood-cells  in  the  main  divisions  of  the 
Vertebrata  The  fractions  are  those  of  an  inch,  and  represent  the  average  diameter.  In  the  case 
of  the  oval  cells,  only  the  long  diameter  is  here  given,  it  is  remarkable,  that  although  the  size  of 
the  red  blood-cells  varies  so  much  in  the  different  classes  of  the  vertebrate  kingdom,  that  of  the 
white  corpuscles  remains  comparatively  uniform,  and  thus  they  are,  in  some  animals,  much  great- 
er, in  others  much  less  than  the  red  corpuscles  existing  side  by  side  with  them. 

nucleus  becomes  strongly  granulated,  and  all  the  coloring  matter  seems 
to  be  concentrated  in  it,  the  surrounding  cell-substance  and  outline  of 


THE    BLOOD.  7" 

the  cell  becoming  almost  invisible;  after  a  time  the  cells  lose  their  color 
altogether.  The  cells  in  the  figure  (Fig.  69)  represent  the  successive 
stages  of  the  change.  A  similar  loss  of  color  occurs  in  the  red  cells  of 
human  blood,  which,  however,  from  the  absence  of  nuclei,  seem  to  dis- 
appear entirely. 

iv.  Alkalies  cause  the  red  blood-cells  to  swell  and  finally  disappear. 

v.  Chloroform  added  to  the  red  blood-cells  of  the  frog  causes  them 
to  part  with  their  haemoglobin;  the  stroma  of  the  cells  becomes  gradually 
broken  up.     A  similar   effect  is  produced  on  the  human  red  blood-cell. 

vi.  Tannin. — When  a  2  per  cent  solution  of  tannic  acid  is  applied  to 
frog's  blood  it  causes  the  appearance  of  a  sharply-defined  little  knob, 
projecting  from  the  free  surface  (Robert's  macula):  the  coloring  matter 
becomes  at  the  same  time  concentrated  in  the  nucleus,  which  grows 
more  distinct  (Fig.  70).  A  somewhat  similar  effect  is  produced  on  the 
human  red  blood-corpuscle. 

vii.  Magenta,  when  applied  to  the  red  blood-cells  of  the  frog,  pro- 
duces a  similar  little  knob  or  knobs,  at  the  same  time  staining  the  nu- 
cleus and  causing  the  discharge  of  the  haemoglobin.  The  first  effect  of 
the  magenta  is  to  cause  the  discharge  of  the  haemoglobin,  then  the 
nucleus  becomes  suddenly  stained,  and  lastly  a  finely  granular  matter 
issues  through  the  wall  of  the  corpuscle,  becoming  stained  by  the  ma- 


Fig.  09.  Fig.  70.  Fig.  71.  Fig.  72  Fig.  78. 

genta,  and  a  macula  is  formed  at  the  point  of  escape.  A  similar  macula 
is  produced  in  the  human  red  blood-cell. 

viii.  Boracic  acid. — A  2  per  cent  solution  applied  to  nucleated  red 
blood-cells  (frog)  will  cause  the  concentration  of  all  the  coloring  matter 
in  the  nucleus;  the  colored  body  thus  formed  gradually  quits  its  central 
position,  and  comes  to  be  partly,  sometimes  entirely,  protruded  from 
the  surface  of  the  now  colorless  cell  (Fig.  71).  The  result  of  this  ex- 
periment Jed  Brucke  to  distinguish  the  colored  contents  of  the  cell 
(zooid)  from  its  colorless  stroma  (cecoid).  When  applied  to  the  non- 
nucleated  mammalian  corpuscle  its  effect  merely  resembles  that  of  other 
dilute  acids. 

ix.  Ammonia. — Its  effects  seem  to  vary  according  to  the  degree  of 
concentration.  Sometimes  the  outline  of  the  corpuscles  becomes  dis- 
tinctly crenated;  at  other  times  the  effect  resembles  that  of  boracic  acid, 
while  in  other  cases  the  edges  of  the  corpuscles  begin  to  break  up. 

Gases.  Carbonic  acid. — If  the  red  blood-cells  of  a  frog  be  first  ex- 
posed to  the  action  of  water-vapor  (which  renders  their  outer  pellicle 
more  readily  permeable  to  gases),  and  then  acted  on  by  carbonic  acid, 
the  nuclei  immediately  become  clearly  defined  and  strongly  granulated: 
when  air  or  oxygen  is  admitted  the  original  appearance  is  at  once  re- 
stored. The  upper  and  lower  cell  in  Fig.  72  show  the  effect  of  carbonic 
acid;  the  middle  one  the  effect  of  the  re-admission  of  air.     These  effects 


74  HANDBOOK   OF   PHYSIOLOGY. 

can  be  reproduced  five  or  six  times  in  succession.  If,  however,  the  ac- 
tion of  the  carbonic  acid  be  much  prolonged,  the  granulation  of  the 
nucleus  becomes  permanent;  it  appears  to  depend  on  a  coagulation  of 
the  paraglobulin. 

Heat.— The  effect  of  heat  up  to  120°-140°  F.  (50°-60°  C.)  is  to 
cause  the  formation  of  a  number  of  bud-like  processes  (Fig.  73). 

Electricity  causes  the  red  blood-corpuscles  to  become  crenated,  and 
at  length  mulberry-like.  Finally  they  recover  their  round  form  and 
become  quite  pale. 

The  Colorless  Corpuscles. — In  human  blood  the  white  or  colorless 
corpuscles  or  leucocytes  are  nearly  spherical  masses  of  granular  proto- 
plasm without  cell  wall.  The  granular  appearance  more  marked  in 
some  than  in  others  {vide  infra),  is  due  to  the  presence  of  particles 
probably  of  a  fatty  nature.  In  all  cases  one  or  more  nuclei  exist  in  each 
corpuscle.  The  size  of  the  corpuscle  averages  xsVo-  of  an  inch  in 
diameter. 

In  health,  the  proportion  of  red  to  white  corpuscles,  which,  taking  an 


Fig.  74.— A.  Three  colored  blood-corpuscles.    B.  Three  colorless  blood-corpuscles  acted  on  by 
acetic  acid  ;  the  nuclei  are  very  clearly  visible,     x  900. 

average,  is  about  1  to  500  or  600,  varies  considerably  even  in  the  course 
of  the  same  day.  The  variations  appear  to  depend  chiefly  on  the 
amount  and  probably  also  on  the  kind  of  food  taken;  the  number  of 
leucocytes  being  very  considerably  increased  by  a  meal,  and  diminished 
again  on  fasting.  Also  in  young  persons,  during  pregnancy,  and  after 
great  loss  of  blood,  there  is  a  larger  proportion  of  colorless  blood-corpus- 
cles, which  probably  shows  that  they  are  more  rapidly  formed  under 
these  circumstances.  In  old  age,  on  the  other  hand,  their  proportion  is 
diminished. 

Varieties. — The  colorless  corpuscles  present  greater  diversities  of 
form  than  the  red  ones.  Two  chief  varieties  are  to  be  seen  in  human 
blood;  one  which  contains  a  considerable  number  of  granules,  and  the 
other  which  is  paler  and  less  granular.  In  size  the  variations  are  great, 
for  in  most  specimens  of  blood  it  is  possible  to  make  out,  in  addition  to 
the  full-sized  varieties,  a  number  of  smaller  corpuscles,  consisting  of  a 
large  spherical  nucleus  surrounded  by  a  variable  amount  of  more  or  less 
granular  protoplasm.  The  small  corpuscles  are,  in  all  probability,  the 
undeveloped  forms  of  the  others,  and  are  derived  from  the  cells  of  the 
lymph. 

Besides  the   above-mentioned    varieties,   Schmidt  describes  another 


THE    BLOOD,  7.5 

form  which  he  looks  upon  as  intermediate  between  the  colored  and  the 
colorless  forms,  viz.,  certain  corpuscles  which  contain  red  granules  of 
haemoglobin  in  their  protoplasm.  The  different  varieties  of  colorless 
corpuscles  are  especially  well  seen  in  the  blood  of  frogs,  newts,  and  other 
cold-blooded  animals. 

Amoeboid  movement. — The  remarkable  property  of  the  colorless 
corpuscles  of  spontaneously  changing  their  shape  was  first  demonstrated 
by  Wharton  Jones  in  the  blood  of  the  skate.  If  a  drop  of  blood  be 
examined  with  a  high  power  of  the  microscope  on  a  warm  stage,  or,  in 
other  words,  under  conditions  by  which  loss  of  moisture  is  prevented, 
and  at  the  same  time  the  temperature  is  maintained  at  about  that  of  the 
blood  within  the  walls  of  the  living  vessels,  100°  F.  (37.8°  C),  the 
colorless  corpuscles  will  be  observed  slowly  to  alter  their  shapes,  and  to 
send  out  processes  at  various  parts  of  their  circumference.  The  amoeboid 
movement  can  be  most  conveniently  studied  in  the  newt's  blood.  The 
processes  which  are  sent  out  from  the  corpuscle  are  either  lengthened  or 
withdrawn.  If  lengthened,  the  protoplasm  of  the  whole  corpuscle  flows 
as  it  were  into  its  process,  and  the  corpuscle  changes  its  position;  if 
withdrawn,  protrusion  of  another  process  at  a  different  point  of  the  cir- 


Fig.  75.— Human  colorless  blood-corpuscle,  showing  its  successive  changes  of  outline  within  ten 
minutes  when  kept  moist  on  a  warm  stage.    (Schofield.) 

cumference  speedily  follows.  The  change  of  position  of  the  corpuscle 
can  also  take  place  by  a  flowing  movement  of  the  whole  mass,  and  in 
this  case  the  locomotion  is  comparatively  rapid.  The  activity  both  in 
the  processes  of  change  of  shape  and  also  of  change  in  position,  is  much 
more  marked  in  some  corpuscles,  viz.,  in  the  granular  variety  than  in 
•others.  Klein  states  that  in  the  newt's  blood  the  changes  are  especially 
likely  to  occur  in  a  variety  of  the  colorless  corpuscle,  which  consists  of 
masses  of  finely  granular  protoplasm  with  jagged  outline,  containing 
three  or  four  nuclei,  or  of  large  irregular  masses  of  protoplasm  contain- 
ing from  five  to  twenty  nuclei.  Another  phenomenon  may  be  observed 
in  such  a  specimen  of  blood,  viz.,  the  division  of  the  corpuscles,  which 
occurs  in  the  following  way.  A  cleft  takes  place  in  the  protoplasm  at 
one  point,  which  becomes  deeper  and  deeper,  and  then  by  the  lengthen- 
ing out  and  attenuation  of  the  connection,  and  finally  by  its  rupture,  two 
corpuscles  result.  The  nuclei  have  previously  undergone  division.  The 
cells  so  formed  are  remarkably  active  in  their  movements.  Thus  we  see 
that  the  rounded  form  which  the  colorless  corpuscles  present  in  ordinary 
microscopic  specimens  must  be  looked  upon  as  the  shape  natural  to  a  dead 
corpuscle  or  to  one  whose  vitality  is  dormant  rather  than  as  the  shape 
proper  to  one  living  and  active. 


Tti  HANDBOOK    OF    PHYSIOLOGY. 

Action  of  reagents  upon  the  colorless  corpuscles.  —Feeding 
the  corpuscles. — If  some  fine  pigment  granules,  e.g.,  powdered  vermilion, 
be  added  to  a  fluid  containing  colorless  blood- corpuscles,  on  a  glass  slide, 
these  will  be  observed,  under  the  microscope,  to  take  up  the  pigment. 
In  some  cases  colorless  corpuscles  have  been  seen  with  fragments  of 
colored  ones  thus  imbedded  in  their  substance.  This  property  of  the 
colorless  corpuscles  is  especially  interesting  as  helping  still  further  to 
connect  them  with  the  lowest  forms  of  animal  life,  and  to  connect  both 
with  the  organized  cells  of  which  the  higher  animals  are  composed. 

The  property  which  the  colorless  corpuscles  possess  of  passing  through 
the  walls  of  the  blood-vessels  will  be  described  later  on. 

Enumeration  of  the  blood-corpuscles.— Several  methods  are  em- 
ployed for  counting  the  blood-corpuscles,  most  of  them  depending  upon 
the  same  principle,  i.e.,  the  dilution  of  a  minute  volume  of  blood  with 
a  given  volume  of  a  colorless  solution  similar  in  specific  gravity  to  blood 
plasma,  so  that  the  size  and  shape  of  the  corpuscles  is  altered  as  little  as 
possible.  A  minute  quantity  of  the  well-mixed  solution  is  then  taken, 
examined  under  the  microscope,  either  in  a  flattened  capillary  tube 
(Malassez)  or  in  a  cell  (Hayem  &  Nachet,"  Gowers)  of  known  capacity, 
and  the  number  of  corpuscles  in  a  measured  length  of  the  tube,  or  in  a 
given  area  of  the  cell  is  counted.  The  length  of  the  tube  and  the  area 
of  the  cell  are  ascertained  by  means  of  a  micrometer  scale  in  the  micro- 
scope ocular;  or  in  the  case  of  Gowers'  modification,  by  the  division  of 
the  cell  area  into  squares  of  known  size.  Having  ascertained  the  number 
of  corpuscles  in  the  diluted  blood,  it  is  easy  to  find  out  the  number  in  a 
given  volume  of  normal  blood.  Gowers'  modification  of  Hayem  & 
Nachet's  instrument,  called  by  him  "  Hcemacytometer,"  appears  to  be  the 
most  convenient  form  of  instrument  for  counting  the  corpuscles,  and  as 
such  will  alone  be  described  (Fig.  76).  It  consists  of  a  small  pipette 
(a),  which,  when  filled  up  to  a  mark  on  its  stem,  holds  995  cubic  milli- 
metres. It  is  furnished  with  an  india-rubber  tube  and  glass  mouth-piece 
to  facilitate  filling  and  emptying;  a  capillary  tube  (b)  marked  to  hold  5 
cubic  millimetres,  and  also  furnished  with  an  india-rubber  tube  and 
mouth-piece;  a  small  glass  jar  (d)  in  which  the  dilution  of  the  blood  is 
performed;  a  glass  stirrer  (e)  for  mixing  the  blood  thoroughly,  (f)  a 
needle,  the  length  of  which  can  be  regulated  by  a  screw;  a  brass  stage 
plate  (c)  carrying  a  glass  slide,  on  which  is  a  cell  one-fifth  of  a  millimetre 
deep,  and  the  bottom  of  which  is  divided  into  one-tenth  millimetre 
squares.  On  the  top  of  the  cell  rests  the  cover-glass,  which  is  kept  in 
its  place  by  the  pressure  of  two  springs  proceeding  from  the  stage  plate. 
A  standard  saline  solution  of  sodium  sulphate,  or  similar  salt,  of  specific 
gravity  1025,  is  made,  and  995  cubic  millimetres  are  measured  by  means 
of  the  pipette  into  the  glass  jar,  and  with  this  five  cubic  millimetres  of 
blood,  obtained  by  pricking  the  finger  with  a  needle,  and  measured  in  the 
capillary  pipette  (B),  are  thoroughly  mixed  by  the  glass  stirring-rod.  A 
drop  of  this  diluted  blood  is  then  placed  in  the  cell  and  covered  with  a 
cover-glass,  which  is  fixed  in  position  by  means  of  the  two  lateral  springs. 
The  preparation  is  then  examined  under  a  microscope  with  a  power  of 
about  400  diameters,  and  focussed  until  the  lines  dividing  the  cell  into 
squares  are  visible. 


THE    BLOOD. 


77 


After  a  short  delay,  the  red  corpuscles  which  have  sunk  to  the  bottom 
•of  the  cell,  and  are  resting  on  the  squares,  are  counted  in  ten  squares, 
and  the  number  of  white  corpuscles  noted.  By  adding  together  the 
numbers  counted  in  ten  (one-tenth  millimetre)  squares,  and  multiplying 


Fig.  76.— Hemacytometer. 

by  ten  thousand,  the  number  of  corpuscles  in  one  cubic  millimetre  of 
blood  is  obtained.  The  average  number  of  corpuscles  per  each  cubic 
millimetre  of  healthy  blood,  according  to  Vierordt  and  Welcker,  is 
5,000,000  in  adult  men,  and  rather  fewer  in  women. 


Chemical  Composition  of  the  Blood. 

Before  considering  the  chemical  composition  of  the  blood  as  a  whole, 
it  will  be  convenient  to  take  in  order  the  composition  of  the  various 
chief  factors  which  have  been  set  out  in  the  table  on  p.  58,  into  which 
the  blood  may  be  separated,  viz. : — (1.)  The  Plasma  ;  (2.)  The  Serum  ; 
(3.)   The  Corpuscles;  (4.)  The  Fibrin. 

(1.)  Chemical  Composition  of  Plasma. — The  Plasma,  or  liquid 
part  of  the  blood,  in  which  the  corpuscles  float,  may  be  obtained  free 
from  colored  corpuscles  in  either  of  the  ways  mentioned  below. 

In  it  are  the  fibrin  factors,  inasmuch  as  when  exposed  to  the  ordinary 
temperature  of  the  air  it  undergoes  coagulation  and  splits  up  into  fibrin 
and  serum.  It  differs  from  the  serum  in  containing  fibrinogen,  but  in 
appearance  and  in  reaction  it  closely  resembles  that  fluid;  its  alkalinity, 
however,  is  less  than  that  of  the  serum  obtained  from  it.  It  may  be 
freed  from  white  corpuscles  by  filtration  at  a  temperature  below  41°  F. 
(5°  C),  or  by  the  centrifugal  machine. 


78  HAXDBOOK    OF  PHYSIOLOGY. 

The  chief  methods  of  obtaining  plasma  free  from  corpuscles  are : 
(1)  by  cold,  the  temperature  should  be  about  0°  C.  and  may  be  two  or 
three  degrees  higher,  but  not  lower.  (2)  The  addition  of  neutral  salts, 
in  certain  proportions,  either  solid  or  in  solution,  e.  g.,  of  sodium  sul- 
phate, if  solid,  1  part  to  12  parts  of  blood;  if  a  saturated  solution,  1  part 
to  6  parts  of  blood;  of  magnesium  sulphate,  of  a  23$,  or  if  saturated 
solution  1  part  to  4  of  blood.  (3)  A  third  way  is  to  mix  frog's  blood 
with  an  equal  part  of  a  5f0  of  cane  sugar,  and  to  get  rid  of  the  corpuscles 
by  filtration;  or  (4)  by  the  injection  of  peptone  into  the  veins  of  mam- 
mals, previous  to  bleeding  them  to  death,  and  afterwards  subjecting  the 
plasma  thus  obtained  to  the  action  of  a  centrifugal  machine. 

Salts  of  the  plasma. — In  1000  parts  of  the  plasma  there  are: — 
Sodium  chloride,     .         .         .         .  ■       .         .         .     5.546 

Soda,  ........  1.532 

Sodium  phosphate,  ......       .271 

Potassium  chloride,     .  ....  .359 

sulphate, 281 

Calcium  phosphate,     .         .         .         .         .         .  .298 

Magnesium  phosphate,    .         .         ...         .         .       .218 


8.505 
(2.)  Chemical  Composition  of  Serum.— The  serum  is  the  liquid 
part  of  the  blood  or  of  the  plasma  remaining  after  the  separation  of  the 
clot.  It  is  an  alkaline,  yellowish,  transparent  fluid,  with  a  specific 
gravity  of  from  1025  to  1032.  In  the  usual  mode  of  coagulation,  part 
of  the  serum  remains  in  the  clot,  and  the  rest,  squeezed  from  the  clot 
by  its  contraction,  lies  around  it.  Since  the  contraction  of  the  clot  may 
continue  for  thirty-six  or  more  hours,  thu  quantity  of  serum  in  the 
blood  cannot  be  even  roughly  estimated  till  this  period  has  elapsed. 
There  is  nearly  as  much,  by  weight,  of  serum  as  there  is  clot  in  coagu- 
lated blood. 

Serum  may  be  obtained  from  blood  corpuscles  by  allowing  blood  to 
clot  in  large  test  tubes,  and  subjecting  the  test  tubes  to  the  action  of  a 
centrifugal  machine  for  some  time. 

In  tabular  form  the  composition  may  be  thus  summarized.  In  1000 
parts  of  serum  there  are: — 

Water, about  900 

Proteids  : 

a.  Serum-albumin,        .         .         .         .         .         •        l    «o 

(5.  Paraglobulin,        ...... 

Salts.  _ 

Fats — including  fatty  acids,  cholesterin,  lecithin  ;  and 
some  soaps,  ....... 

Grape  sugar  in  small  amount,    ..... 

Extractives — kreatin,  kreatinin,  urea,  etc.,    .         .  \   20 
Yellow  pigment,  which  is  independent  of  haemoglobin, 
Gases — small  amounts  of  oxygen,   nitrogen,    and  car- 
bonic acid,        

1000 


THE    BLOOD.  79 

a.  Water. — The  water  of  the  serum  varies  in  amount  according  to 
the  amount  of  food,  drink,  and  exercise,  and  with  many  other  circum- 
stances. 

b.  Proteids. — a.  Serum-albumin  is  the  chief  proteid  found  in  serum. 
The  proportion  which  it  bears  to  paraglobulin,  the  other  proteid,  is  as 
1.011  to  1.  in  human  blood. 

Serum-albumin  has  been  shown  by  Halliburton  to  be  a  compound 
body,  which  may  be  called  serine,  made  up  of  three  proteids,  which  co- 
agulate at  different  temperatures,  a  at  73°  C. ,  ft  at  77°  C,  and  y  at  85°  C. 
The  serine  is  entirely  coagulated  at  94°  C,  and  also  by  the  addition  of 
strong  acids,  such  as  nitric  and  hydrochloric  ;  by  long  contact  with  al- 
cohol it  is  precipitated.  It  is  not  precipitated  on  addition  of  ether,  and 
so  differs  from  the  other  native  albumin,  viz.,  e^-albumin.  When  dried 
at  104°  F.  (40°  C.)  serum-albumin  is  a  brittle,  yellowish  substance,  solu- 
ble in.  water,  possessing  a  laevorotary  power  of  —56°.  It  is  with  great 
difficulty  freed  from  its  salts,  and  is  precipitated  by  solutions  of  metallic 
salts,  e.g.,  of  mercuric  chloride,  copper  sulphate,  lead  acetate,  sodium 
tungstate,  etc.  If  dried  at  a  temperature  over  35°  C.  the  residue  is  insol- 
uble in  water,  having  been  changed  into  coagulated  proteid.  Serum- 
albumin  may  be  precipitated  from  serum,  from  which  the  paraglobulin 
has  been  previously  separated  by  saturation  with  magnesium  sulphate, 
and  removed  by  filtration,  by  further  saturation  with  sodium  sulphate, 
sodium  nitrate,  or  iodide  of  potassium. 

ft.  Paraglobulin  can  be  obtained  as  a  white  jorecipitate  from  cold  serum 
by  adding  a  considerable  excess  of  water,  and  passing  through  the  mix- 
ture a  current  of  carbonic  acid  gas  or  by  the  cautious  addition  of  dilute 
acetic  acid.  It  can  also  be  obtained  by  saturating  serum  with  either 
crystallized  magnesium  sulphate,  or  sodium  chloride,  nitrate,  acetate,  or 
carbonate.  When  obtained  in  the  latter  way,  precipitation  seems  to  be 
much  more  complete  than  by  means  of  the  former  method.  Paraglobu- 
lin belongs  to  the  class  of  proteids  called  globulins. 

c.  The  salts  of  sodium  predominate  in  serum  as  in  plasma,  and  of 
these  the  chloride  generally  forms  by  far  the  largest  proportion. 

d.  Fats  are  present  partly  as  fatty  acids  and  partly  emulsified.  The 
fats  are  tri-olein,  tri-stearin,  tri-palmitin.  The  amount  of  fatty  matter 
varies  according  to  the  time  after,  and  the  ingredients  of,  a  meal.  Of 
cliolesterin  and  lecithin  there  are  mere  traces. 

e.  Grape  sugar  is  found  principally  in  the  blood  of  the  hepatic  vein, 
about  one  part  in  a  thousand. 

f.  The  extractives  vary  from  time  to  time  ;  sometimes  uric  and  hip- 
puric  acids  are  found  in  addition  to  urea,  kreatin,  and  kreatinin.  Urea 
exists  in  proportion  from  .02  to  .04  per  cent. 

g.  The  yellow  pigment  of  the  serum  and  the  odorous  matter  which 
gives  the  blood  of  each  particular  animal  a  peculiar  smell,  have  not 
yet  been  exactly  differentiated.  The  former  is  probably  choletelin 
(MacMunn). 


SO  HANDBOOK   OF    PHYSIOLOGY. 

(3.)  Chemical  Composition  of  the  Corpuscles.— a.  Colored. — 
Analysis  of  a  thousand  parts  of  moist  blood-corpuscles  shows  the  follow- 
ing result: — 

Water, 688 

Solids— 

S  Organic, 303.88 

(Mineral, 8.12—312  =  1000. 

Of  the  solids  the  most  important  is  Haemoglobin,  the  substance  to 
which  the  blood  owes  its  color.  It  constitutes,  as  will  be  seen  from  the 
appended  Table,  more  than  90  per  cent  of  the  organic  matter  of  the 
corpuscles.  Besides  haemoglobin  there  are  proteid  *  and  fatty  matters, 
the  former  chiefly  consisting  of  globulins,  and  the  latter  of  cholesterin 
and  lecithin. 

In  1000  parts  organic  matter  are  found  : — 

Haemoglobin, 905.4 

Proteids, .86.7 

Fats, 7-9  =  1000 

Of  the  inorganic  salts  of  the  corpuscles,  with  the  iron  omitted — 
In  1000  parts  corpuscles  (Schmidt)  are  found  : — 

Potassium  Chloride, 3.679 

Potassium  Phosphate, 2. 343 

Potassium  sulphate, 132 

Sodium,      ........  .633 

Calcium, 094 

Magnesium,        .         .         .         .         .         .         .  .060 

Soda, 341  =  7.282 

The  properties  of  haemoglobin  will  be  considered  in  relation  to  the 
Gases  of  the  blood  (p.  83). 

b.  Colorless. — The  corpuscles  may  be  said  also  to  contain  fibrinogen, 
paraglobulin,  and  the  ferment.  In  consequence  of  the  difficulty  of  ob- 
taining colorless  corpuscles  in  sufficient  number  to  make  an  analysis , 
little  is  accurately  known  of  their  chemical  composition;  in  all  proba- 
bility, however,  the  stroma  of  the  corpuscles  is  made  up  of  proteid  mat- 
ter, and  the  nucleus  of  nuclein,  a  nitrogenous, -phosphorus-containing 
body  akin  to  mucin,  capable  of  resisting  the  action  of  the  gastric  juice. 
The  proteid  matter,  chiefly  globulins,  soluble  in  a  ten  per  cent  solution 
of  sodium  chloride,  the  solution  being  precipitated  on  the  addition  of 
water,  by  heat  and  by  the  mineral  acids.  The  stroma  contains  fatty 
granules,  and  in  it  also  the  presence  of  glycogen  has  been  demonstrated. 
The  salts  of  the  corpuscles  are  chiefly  potassium,  and  of  these  the  phos- 
phate is  in  greatest  amount. 

1  An  account  of  the  proteid  bodies,  etc.,  will  be  found  in  the  Appendix,  and  should 
be  referred  to  for  explanation  of  the  terms  employed  in  the  text. 


THE    BLOOD. 


bl 


(4.)  Chemical  Composition  of  Fibrin.— The  part  played  by  fibrin 
in  the  formation  of  a  clot  has  been  already  described  (p.  58),  and  it  is 
only  necessary  to  consider  here  its  general  properties.  It  is  a  stringy 
elastic  substance  belonging  to  the  proteid  class  of  bodies.  It  is  insoluble 
in  water  and  in  weak  saline  solutions  ;  soluble  in  ten  per  cent  solu- 
tion of  sodium  chloride,  it  swells  up  into  a  transparent  jelly  when 
placed  in  dilute  hydrochloric  acid,  but  does  not  dissolve,  but  in  strong 
acid  it  dissolves,  producing  acid-albumin  '  ;  it  is  also  soluble  in  strong 
saline  solutions.  Blood  contains  only  .2  per  cent  of  fibrin.  It  can  be 
converted  by  the  gastric  or  pancreatic  juice  into  peptone.  It  possesses 
the  power  of  liberating  the  oxygen  from  solutions  of  hydric  peroxide, 
H2Oa  or  ozonic  ether.  This  may  be  shown  by  dipping  a  few  shreds  of 
fibrin  in  tincture  of  guaiacum,  and  then  immersing  them  in  a  solution 
of  hydric  peroxide.  The  fibrin  becomes  of  a  bluish  color,  from  its  hav- 
ing liberated  from  the  solution  oxygen,  which  oxidizes  the  resin  of  guai- 
acum contained  in  the  tincture,  and  thus  produces  the  coloration. 

The  Gases  of  the  Blood. 

The  gases  contained  in  the  blood  are  Carbonic  acid,  Oxygen,  and 
Nitrogen,  100  volumes  of  blood  containing  from  50  to  60  volumes  of 
these  gases  collectively. 

Arterial  blood  contains  relatively  more  oxygen  and  less  carbonic  acid 
than  venous.  But  the  absolute  quantity  of  carbonic  acid  is  in  both 
kinds  of  blood  greater  than  that  of  the  oxygen. 

Oxygen.  Carbonic  Acid.  Nitrogen. 

Arterial  Blood,     .     .     20  vol.  per  cent  39  vol.  per  cent  1  to  2  Vols. 
Venous       " 

(from  muscles  at  rest)  8  to  12    "      "      "  4G    "      "      "  1  to  2  vols. 

The  Extraction  of  the  Oases  frOm  the  Blood.  —  As  the  ordinary  air- 
pumps  are  not  sufficiently  powerful  for  the  purpose,  the  extraction  of 
the  gases  from  the  blood  is  accomplished  by  means  of  a  mercurial  air- 
pump,  of  which  there  are  many  varieties,  those  of  Ludwig,  Alvergnidt, 
Geissler,  and  Sprengel  being  the  chief.  The  principle  of  action  in  all  is 
much  the  same.  Lud  wig's  pump,  which  may  be  taken  as  a  type,  is  rep- 
resented in  Fig.  77.  It  consists  of  two  fixed  glass  globes,  Cand  F,  the 
upper  one  communicating  by  means  of  the  stop-cock  D,  and  a  stout  in- 
dia-rubber tube  with  another  glass  globe,  L,  which  can  be  raised  or 
lowered  by  means  of  a  pulley  ;  it  also  communicates  by  means  of  a  stop- 
cock, B,  and  a  bent  glass  tube,  A.  with  a  gas  receiver  (not  represented 
in  the  figure),  A,  dipping  into  a  bowl  of  mercury,  so  that  the  gas  mav  be 
received  over  mercury.     The  lower  globe,  F,  communicates  with  C  by 

1  The  use  of  the  two  words  albumen  and  albumin  may  need  explanation.     The 
former  is  the  generic  word,  which  may  include  several  albuminous  or  proteid  bodies, 
e.  r/.,  albumen  of  blood;   the  latter  which  requires  to  be  qualified  by  another  word  is 
the  specific  form,  and  is  applied  to  varieties,  e.  g.,  egg-albumin,  serum-albumin. 
6 


HANDBOOK    OF    PHYSIOLOGY. 


means  of  the  stopcock,  E,  with  Jin  which  the  blood  is  contained  by  the 
stopcock,  G,  and  with  a  movable  glass  globe,  M,  similar  to  L,  by  means 
of  the  stopcock,  H,  and  the  stout  india-rubber  tube,  K. 

In  order  to  work  the  pump,  L  and  M  are  filled  with  mercury,  the 
blood  from  which  the  gases  are  to  be  extracted  is  placed  in  the  bulb  I, 
the  stopcocks,  H,  E,  D,  and  B,  being  open,  and  G  closed.  M  is  raised 
by  means  of  the  pulley  until  J7  is  full  of  mercury,  and  the  air  is  driven 
out.  E  is  then  closed,  and  L  is  raised  so  that  C becomes  full  of  mer- 
cury, and  the  air  driven  off.  B  is  then  closed.  On  lowering  L  the 
mercury  runs  into  it  from  C,  and  a  vacuum  is  established  in  G.  On 
opening  E  and  lowering  M,  a  vacuum  is  similarly  established  in  F;  if  G. 
be  now  opened,  the  blood  in  I  will  enter  into  ebullition,  and  the  gases 

will  pass  off  into  F  and  C,  and  on  raising  M 
and  then  X,  the  stopcock  B  being  opened, 
the  gas  is  driven  through  A,  and  is  received 
into  the  receiver  over  mercury.  By  repeat- 
ing the  experiment  several  times  the  whole 
of  the  gases  of  the  specimen  of  blood  is 
obtained,  and  may  be  estimated. 

a.  The  Oxygen  of  the  Blood. — It  has 
been  found  that  a  very  small  proportion  of 
the  oxygen  which  can    be  obtained,  by  the 
aid  of  the  mercurial  pump,  from  the  blood, 
exists  in  a  state  of   simple   solution  in  the 
plasma.     If  the  gas  were  in  simple  solution, 
the  amount  of  oxygen  in  any  given  quantity 
of  blood   exposed   to  any  given  atmosphere 
ought  to  vary  with   the  amount   of  oxygen 
contained  in  the  atmosjDhere.     Since,  speak- 
ing generally,    the  amount   of  any  gas   ab- 
sorbed by  a  liquid  such  as  plasma  would  de- 
pend upon  the  proportion  of  the  gas  in  the 
atmosphere  to  which  the  liquid  is  exposed — 
if  the  proj)ortion  is  great,  the  absorption  will 
be   great;  if   small,  the   absorption   will   be 
similarly  small.     The   absorption  continues 
until    the    proportions   of    the   gas    in   the 
liquid   and   in    the   atmosphere   are   equal. 
Other  things  will,  of  course,  influence  the 
absorption,  such  as  the  nature  of  the  gas  employed,  the  nature  of  the 
liquid,  and  the  temperature,  but  cceteris  paribus,  the  amount  of  a  gas 
which  a  liquid  absorbs  depends  upon  the  proportion— the  so-called  par- 
tial pressure — of   the   gas   in   the   atmosphere   to  which   the   liquid   is 
subjected.     And  conversely,  if  a  liquid  containing  a  gas  in  solution  be 
exposed  to  an  atmosphere  containing  none  of  the  gas,  the  gas  will  be 
given  up  to  the  atmosphere  until  the  amount  in  the  liquid  and  in  the 


Fig.  77.— Ludwig's  Mercurial 
Pump. 


THK   BLOOD.  83 

atmosphere  becomes  equal.     This  condition  is  called  a  condition  of  equal 
tensions. 

The  condition  may  be  understood  by  a  simple  illustration.  A  large 
amount  of  carbonic  acid  gas  is  dissolved  in  a  bottle  of  water  by  exposing 
the  liquid  to  extreme  pressure  of  the  gas,  and  a  cork  is  placed  in  the 
bottle  and  wired  down.  The  gas  exists  in  the  water  in  a  condition  of 
extreme  tension,  and  therefore  exhibits  a  tendency  to  escape  into  the 
atmosphere,  in  order  to  relieve  the  tension;  this  produces  the  violent 
expulsion  of  the  cork  when  the  wire  is  removed,  and  if  the  aerated  water 
be  placed  in  a  glass  the  gas  will  continue  to  be  evolved  until  it  has  almost 
entirely  passed  into  the  atmosphere,  and  the  tension  of  the  gas  in  the 
water  approximates  to  that  of  the  atmosphere  in  which,  it  should  be 
remembered,  the  carbon  dioxide  is,  naturally,  in  very  small  amount, 
viz.,  .04  per  cent. 

The  oxygen  of  the  blood  does  not  obey  this  law  of  pressure.  For  if 
blood  which  contains  little  or  no  oxygen  be  exposed  to  a  succession  of 
atmospheres  containing  more  and  more  of  that  gas,  we  find  that  the 
absorption  is  at  first  very  great,  but  soon  becomes  relatively  very  small, 
not  being  therefore  regularly  in  proportion  to  the  increased  amount  (or 
tension)  of  the  oxygen  of  the  atmospheres,  and  that  conversely,  if  arte- 
rial blood  be  submitted  to  regularly  diminishing  pressures  of  oxygen,  at 
first  very  little  of  the  contained  oxygen  is  given  off  to  the  atmosphere, 
then  suddenly  the  gas  escapes  with  great  rapidity,  and  again  disobeys 
the  law  of  pressures. 

Very  little  oxygen  can  be  obtained  from  serum  freed  from  blood- 
corpuscles,  even  by  the  strongest  mercurial  air-pump,  neither  can  serum 
be  made  to  absorb  a  large  quantity  of  that  gas;  but  the  small  quantity 
which  is  so  given  up  or  so  absorbed  follows  the  laws  of  absorption 
according  to  pressure. 

It  must  be,  therefore,  evident  that  the  chief  part  of  the  oxygen  is 
contained  in  the  corpuscles,  and  not  in  a  state  of  simple  solution.  The 
chief  solid  constituent  of  the  colored  corpuscles  is  haemoglobin,  which 
constitutes  more  than  90  per  cent  of  their  bulk.  This  body  has  a  very 
remarkable  affinity  for  oxygen,  absorbing  it  to  a  very  definite  extent 
under  favorable  circumstances,  and  giving  it  up  when  subjected  to  the 
action  of  reducing  agents,  or  to  a  sufficiently  low  oxygen  pressure. 
From  these  facts  it  is  inferred  that  the  oxygen  of  the  blood  is  combined 
with  haemoglobin,  and  not  simply  dissolved;  but  inasmuch  as  it  is  com- 
paratively easy  to  cause  the  haemoglobin  to  give  up  its  oxygen,  it  is 
believed  that  the  oxygen  is  but  loosely  combined  with  the  substance. 

Haemoglobin. — Haemoglobin  is  a  crystallizable  body  which  consti- 
tutes by  far  the  largest  portion  of  the  colored  corpuscles.  It  is  inti- 
mately distributed  throughout  their  stroma,  and  must  be  dissolved  out 
before  it  will  undergo  crystallization.     Its   percentage   composition  is 


84 


HANDBOOK    OF    PHYSIOLOGY. 


C.  53.85;  H.  7.32;  K  16.17;  0.  21.84;  S.  .63;  Fe.  .42;  and  if  the 
molecule  be  supposed  to  contain  one  atom  of  iron  the  formula  would  be 
C  ,  H960,  K154,  FeS3  0]79.  The  most  interesting  of  the  properties  of 
haemoglobin  are  its  powers  of  crystallizing  and  its  attraction  for  oxygen 
and  other  gases. 

Crystals. — The  haemoglobin  of  the  blood  of  various  animals  pos- 
sesses the  power  of  crystallizing  to  very  different  extents  (blood- 
crystals).  In  some  animals  the  formation  of  crystals  is  almost  spon- 
taneous, whereas  in  others  it  takes  place  either  with  great  difficulty  or 
not  at  all.  Among  the  animals  whose  blood  coloring-matter  crystallizes 
most  readily  are  the  guinea-pig,  rat,  squirrel,  and  dog;  and  in  these 
cases  to  obtain  crystals  it  is  generally  sufficient  to  dilute  a  drop  of 
recently-drawn  blood  with  water  and  expose  it  for  a  few  minutes  to  the 
air.     Light  seems  to  favor  the  formation  of  the  crystals.     In  many  in- 


Fig.  78.— Crystals  of  oxy-haemoglobin— prismatic  from  human  blood. 

stances  other  means  must  be  adopted,  e.  g.,  the  addition  of  alcohol, 
ether,  or  chloroform,  rapid  freezing,  and  then  thawing,  an  electric  cur- 
rent, a  temperature  of  140°  F.  (60°  C),  or  the  addition  of  sodium 
sulphate. 

The  haemoglobin  of  human  blood  crystallizes  with  difficulty,  as  does 
also  that  of  the  ox,  the  pig,  the  sheep,  and  the  rabbit. 

The  forms  of  haemoglobin  crystals,  as  will  be  seen  from  the  appended 
figures,  differ  greatly. 

Haemoglobin  crystals  are  soluble  in  water.  Both  the  crystals  them- 
selves and  also  their  solutions  have  the  characteristic  color  of  arterial 
blood. 

A  dilute  solution  of  haemoglobin  gives  a  characteristic  appearance 
with  the  spectroscope.  Two  absorption  bands  are  seen  between  the  solar 
lines  d  (which  is  the  sodium  band  in  the  yellow)  and  e  (see  plate),  one  in 
the  yellow,  with  its  middle  line  some  little  way  to  the  right  of  D,  is  very 


THE    BLOOD. 


85 


intense,  but  narrower  than  the  other,  which  lies  in  the  green  near  to  the 
left  of  e.  Each  baud  is  darkest  in  the  middle  and  fades  away  at  the 
sides.  As  the  strength  of  the  solution  increases,  the  bands  become  broader 
and  deeper  and  both  the  red  and  the  blue  euds  of  the  spectrum  become 
encroached  upon  until  the  bands  coalesce  to  form  one  very  broad  band, 
and  only  a  slight  amount  of  the  green  remains  unabsorbed,  and  part  of 
the  red;  on  still  further  increase  of  the  strength  the  former  disappears. 

If  the  crystals  of  oxyhemoglobin  be  subjected  to  a  mercurial  air- 
pump,  they  give  off  a  definite  amount  of  oxygen  (1  gramme  giving 
off  1.59  c.  cm.  of  oxygen),  and  they  become  of  a  purple  color;  and  a 
solution  of  oxy-haemoglobin  may  be  made  to  give  up  oxygen,  and  to  be- 
come purple  in  a  similar  manner. 

This  change  may  be  also  effected  by  passing  through  it  hydrogen  or 


Fig.  79. 


Fig. 


Fig.  79  —  Oxy-hsemoglobin  crystals— tetrahedral,  from  blood  of  the  guinea-pig. 
Fig.  80.— Hexagonal  oxy-hfeuioglobin  crystals,  from  blood  of  squirrel.     On  these  hexagonal 
plates  prismatic  crystals  grouped  in  a  stellate  manner  not  unfrequently  occur  (after  Funke). 

nitrogen  gas,  or  by  the  action  of  reducing  agents,  of  which  Stokes'  fluid  ' 
or  ammonium  sulphide  is  the  most  convenient. 

AVith  the  spectroscope,  a  solution  of  deoxidized  or  reduced  haemo- 
globin is  found  to  give  an  entirely  different  appearance  from  that  of 
oxidized  haemoglobin.  Instead  of  the  two  bands  at  d  and  E  we  find  a 
single  broader  but  fainter  band  occupying  a  position  midway  between  the 
two,  and  at  the  same  time  less  of  the  blue  end  of  the  spectrum  is  ab- 
sorbed. Even  in  strong  solutions  this  latter  appearance  is  found. 
thereby   differing    from   the   strong   solution  of   oxidized    haemoglobin 


1  Stokes'  Fluid  consists  of  a  solution  of  ferrous  sulphate,  to  which  ammonia 
has  been  added  and  sufficient  tartaric  acid  to  prevent  precipitation.  Another 
reducing  agent  is  a  solution  of  stannous  chloride,  treated  in  a  way  similar  to  the 
ferrous  sulphate,  and  a  third  reagent  of  like  nature  is  an  aqueous  solution  of 
ammonium  sulphide.    N  Ht  H  S. 


88  HANDBOOK    OF    PHYSIOLOGY. 

which  lets  through  only  the  red  and  orange  rays;  accordingly  to  the  naked 
eye,  the  one  (reduced  haemoglobin- solution)  appears  purple,  the  other 
(oxy-haemoglobin  solution)  red.  The  deoxidized  crystals  or  their  solu- 
tions quickly  absorb  oxygen  on  exposure  to  the  air,  becoming  scarlet. 
It  solutions  of  blood  be  taken  instead  of  solutions  of  haemoglobin,  results 
similar  to  the  whole  of  the  foregoing  can  be  obtained. 

Venous  blood  never,  except  in  the  last  stages  of  asphyxia,  fails  to  show 
the  oxy-haemoglobin  bands,  inasmuch  as  the  greater  part  of  the  haemo- 
globin even  in  venous  blood,  exists  in  the  more  highly  oxidized  condition. 

Action  of  Gases  on  Haemoglobin.—  Carbonic  oxide  gas,  passed 
through  a  solution  of  haemoglobin,  causes  it  to  assume  a  bluish  color, 
and  its  spectrum  to  be  slightly  altered;  two  bands  are  still  visible,  but 
are  slightly  nearer  the  blue  end  tban  those  of  oxy-haemoglobin  (see 
plate).  The  amount  of  carbonic  oxide  taken  up  is  equal  to  the  amount 
of  the  oxygen  displaced.  Although  the  carbonic  oxide  gas  readily  dis- 
places oxygen,  the  reverse  is  not  the  case,  and  upon  this  property  depends 
the  dangerous  effect  of  coal-gas  poisoning.  Coal  gas  contains  much 
carbonic  oxide,  and  when  breathed,  the  gas  combines  with  the  haemo- 
globin of  the  blood,  and  produces  a  compound  which  cannot  easily  be 
reduced.  This  compound  (carboxy-haemoglobin)  is  by  no  means  an 
oxygen  carrier,  and  death  may  result  from  suffocation  due  to  the  want 
of  oxygen  notwithstanding  the  free  entry  of  pure  air  into  the  lungs. 
Crystals  of  carbonic-oxide  haemoglobin  closely  resemble  those  of  oxy- 
haemoglobin. 

Nitric  oxide  produces  a  similar  compound  to  the  carbonic-oxide 
haemoglobin,  which  is  even  less  easily  reduced. 

Nitrous  oxide  reduces  oxy-hsemoglobin,  and  therefore  leaves  the 
reduced  haemoglobin  in  a  condition  to  actively  take  up  oxygen. 

Sulphuretted  Hydrogen. — If  this  gas  be  passed  through  a  solution  of 
oxy-haemoglobin,  the  haemoglobin  is  reduced  and  an  additional  band 
appears  in  the  red.  If  the  solution  be  then  shaken  with  air,  the  two 
bands  of  oxy-haemoglobin  replace  that  of  reduced  haemoglobin,  but  the 
band  in  the  red  persists. 

Derivatives  of  Haemoglobin. 

Methaemoglobin. — If  an  aqueous  solution  of  oxy-haemoglobin  is  ex- 
posed to  the  air  for  some  time,  its  spectrum  undergoes  a  change;  the 
two  d  and  e  bands  become  faint,  and  a  new  line  in  the  red  at  c  is 
developed.  The  solution,  too,  becomes  brown  and  acid  in  reaction,  and 
is  precipitable  by  basic  lead  acetate.  This  change  is  due  to  the  decom- 
position of  oxy-haemoglobin,  and  to  the  production  of  methcemoglobin 
On  adding  ammonium  sulphide,  reduced  haemoglobin  is  produced,  and 
on  shaking  this  up  with  air,  oxy-haemoglobin  is  reproduced.  Methaemo- 
globin is  probably  a  stage  in  the  deoxidation  of  oxy-haemoglobin.  It 
appears  to  contain  less  oxygen  than  oxy-haemoglobin,  but  more  than 
reduced  haemoglobin.  Its  oxygen  is  in  more  stable  combination,  how- 
ever, than  is  the  case  with  the  former  compound. 

Haematin. — By  the  action  of  heat,  or  of  acids  or  alkalies  in  the 
presence  of  oxygen,  haemoglobin  can  be  split  up  into  a  substance  called 
Hcematin,  which  contains  all  the  iron  of  the  haemoglobin  from  which  it 


THE    BLOOD.  »< 

was  derived,  and  a  proteid  residue.  Of  the  latter  it  is  impossible  to  say 
more  than  that  it  probably  consists  of  one  or  more  bodies  of  the  globulin 
class.  If  there  be  no  oxygen  present,  instead  of  haematin  a  body  called 
haemochromogen  is  produced,  which,  however,  will  speedily  undergo 
oxidation  into  haematin. 

Haematin  is  a  dark  brownish  or  black  non-crystallizable  substance  of 
metallic  lustre.  Its  percentage  composition  is  C.  64.30;  H.  5.50;  N. 
9.06;  Fe.  8.82;  0.  12.32;  which  gives  the  formula  C08,  H70,  N"8,  Fes,  0,„ 
(Hoppe-Seyler).  It  is  insoluble  in  water,  alcohol,  and  ether;  soluble  in 
the  caustic  alkalies;  soluble  with  difficulty  in  hot  alcohol  to  which  is 
added  sulphuric  acid.  The  iron  may  be  removed  from  haematin  by 
heating  it  with  fuming  hydrochloric  acid  to  320°  F.  (160°  C),  and  a 
new  body,  haematoporphyrin,  is  produced.  Haematoporphyrin  (C68, 
H74,  N8,  0)2,  Hoppe-Seyler)  may  also  be  obtained  by  adding  blood  to 
strong  sulphuric  acid,  and  if  necessary  filtering  the  fluid  through 
asbestos.  It  forms  a  fine  crimson  solution,  which  has  a  distinct  spec- 
trum, viz.,  a  dark  band  just  beyond  D,  and  a  second  all  but  midway 
between  d  and  e.  It  may  be  precipitated  from  its  acid  solution  by  adding 
water  or  by  neutralization,  and  when  redissolved  in  alkalies  presents 


Fig.  81.  Fig.  82. 

Fig.  81 .  —  Hcematoidin  crystals.    (Frey.) 
Fig.  82.— Hnemiu  crystals.   (Frey.) 

four  bands,  a  pale  baud  between  c  and  d,  a  second  between  D  and  E, 
nearer  D,  another  nearer  e,  and  a  fourth  occupying  the  chief  part  of 
the  space  between  b  and  F. 

Hcematin  in  arid  solution. — If  an  excess  of  acetic  acid  be  added  to 
blood,  and  the  solution  is  boiled,  the  color  alters  to  brown  from  decom- 
position of  haemoglobin  and  the  setting  free  of  haematin;  by  shaking  this 
solution  with  ether,  solution  of  the  haematin  in  acid  solution  is  obtained. 
The  spectrum  of  the  ethereal  solution  (colored  plate)  shows  no  less  than 
four  absorption  bands,  viz.,  one  in  the  red  between  c  and  d,  one  faint 
and  narrow  close  to  I),  and  then  two  broader  bands,  one  between  d  and 
e,  and  another  nearly  midway  between  b  and  f.  The  first  band  is  by  far 
the  most  distinct,  and  the  acid  aqueous  solution  of  haematin  shows  it 
plainly. 

Hcematin  in  alkaline  solution. — If  an  alkali  be  added  to  blood  and 
the  solution  is  boiled,  alkaline  haematin  is  produced,  and  the  solution 
becomes  olive  green  in  color,  the  absorption  band  of  which  is  still  in  the 
red,  but  nearer  to  D,  and  the  blue  end  of  the  spectrum  is  partially 
absorbed  to  a  considerable  extent.  If  a  reducing  agent  be  added,  fcwo 
bands  resembling  those  of  oxy-haemoglobin,  but  nearer  to  the  blue, 
appear;  this  is  the  spectrum  of  reduced  hcematin,  or  haemochromogen. 


S^  HANDBOOK    OF   PHYSIOLOGY. 

On  shaking  the  reduced  haematin  with  air  or  oxygen  the  two  bands  are 
replaced  by  the  single  band  of  alkaline  haematin. 

Haematoidin. — This  substance  is  found  in  the  form  of  yellowish 
crystals  in  old  blood  extravasations,  and  is  derived  from  the  haemoglobin. 
Their  crystalline  form  and  the  reaction  they  give  with  nitric  acid  seem 
to  show  them  to  be  identical  with  Bilirubin,  the  chief  coloring  matter 
of  the  Bile. 

Haemin. — One  of  the  most  important  derivatives  of  haematin  is  hae- 
min.  It  is  usually  called  Hydrocklorate  of  Hcematin  (or  hydrochloride), 
but  its  exact  chemical  composition  is  uncertain.  Its  formula  is  C68,  H70, 
N,,  Fe2,  O10,  2  HC1,  and  it  contains  5.18  per  cent  of  chlorine,  but  by 
some  it  is  looked  upon  as  simply  crystallized  haematin.  Although  diffi- 
cult to  obtain  in  bulk,  a  specimen  may  be  easily  made  for  the  microscope 
in  the  following  way  :— A  small  drop  of  dried  blood  is  finely  powdered 
with  a  few  crystals  of  common  salt  on  a  glass  slide,  and  spread  out ;  a 
cover  glass  is  then  placed  upon  it,  and  glacial  acetic  acid  added  by  means 
of  a  capillary  pipette.  The  blood  at  once  turns  of  a  brownish  color. 
The  slide  is  then  heated,  and  the  acid  mixture  evaporated  to  dryness  at 
a  high  temperature.  The  excess  of  salt  is  washed  away  with  water  from 
the  dried  residue,  and  the  specimen  may  then  be  mounted.  A  large 
number  of  small,  dark,  reddish  black  crystals  of  a  rhombic  shape,  some- 
times arranged  in  bundles,  will  be  seen  if  the  slide  be  subjected  to  micro- 
scopic examination. 

The  formation  of  these  haemin  crystals  is  of  great  interest  and  impor- 
tance from  a  medico-legal  point  of  view,  as  it  constitutes  the  most  certain 
and  delicate  test  we  have  for  the  presence  of  blood  (not  of  necessity  the 
blood  of  man)  in  a  stain  on  clothes,  etc.  It  exceeds  in  delicacy  even  the 
spectroscopic  test.  Compounds  similar  in  composition  to  haemin,  but 
containing  hydrobromicand  hydriodic  acids,  instead  of  hydrochloric,  may 
be  also  readily  obtained. 

Estimation  of  Haemoglobin. — The  most  exact  method  is  by  the 
estimation  of  the  amount  of  iron  in  a  given  specimen  of  blood,  but  as 
this  is  a  somewhat  complicated  process,  a  method  has  been  proposed 
which,  though  not  so  exact,  has  the  advantage  of  simplicity.  This  con- 
sists in  comparing  the  color  of  a  given  small  amount  of  diluted  blood 
with  glycerin  jelly  tinted  with  carmine  and  picrocarmine  to  represent  a 
standard  solution  of  blood  diluted  one  hundred  times.  The  amount  of 
dilution  which  the  given  blood  requires  will  thus  approximately  repre- 
sent the  quantity  of  haemoglobin  it  contains.     (Gowers.) 

Distribution  of  Haemoglobin. — Haemoglobin  occurs  not  only  in  the 
red  blood-cells  of  all  Vertebrata  (except  one  fish  [leptocephalus]  whose 
blood  cells  are  all  colorless),  but  also  in  similar  cells  in  many  Worms  ; 
moreover,  it  is  found  diffused  in  the  vascular  fluid  of  some  other  worms 
and  certain  Crustacea  ;  it  also  occurs  in  all  the  striated  muscles  of  Mam- 
mals and  Birds.  It  is  generally  absent  from  unstriated  muscle  except 
that  of  the  rectum.     It  has  also  been  found  in  Mollusca  in  certain  mus- 


THE    BLOOD.  8M 

cles  which  are  specially  active,   viz.,  those  which   work  the  rasp-like 
tongue. 

B.  The  Carbon  Dioxide  Gas  in  the  Blood.— Of  this  gas  in  the 
blood,  part  exists  in  a  state  of  simple  solution  in  the  serum,  and  and  the 
rest  in  a  state  of  weak  chemical  combination.  It  is  believed  that  the 
latter  is  combined  with  the  sodium  carbonate  in  a  condition  of  bicar- 
bonate. Some  observers  consider  that  part  of  the  gas  is  associated  with 
the  corpuscles. 

C.  The  Nitrogen  in  the  Blood. — The  whole  of  the  small  quantity 
of  the  nitrogen  contained  in  the  blood  is  simply  dissolved  in  the  fluid 
plasma. 

Chemical  Composition  of  the  Blood  in  Bulk. — Analyses  of  the 
blood  as  a  whole  differ  slightly,  but  the  following  table  may  be  taken  to 
represent  the  average  composition  : 

Water,        .  784 

Solids- 
Corpuscles,      ......         130 

Proteids  (of  serum),     .....      70 

Fibrin  (of  clot), 2.2 

Fatty  matters  (of  serum),   .         .         .       '  .         1.4 
Inorganic  salts  (of  serum),      ...  C 

Gases,    kreatin,    urea    and    other    extractive  )  6.4 — 
matter,  glucose  and  accidental  substances,    \  216 


1000 


Variations  in  the  Composition  of  healthy  Blood. 

The  conditions  which  appear  most  to  influence  the  composition  of 
the  blood  in  health  are  these  :  Sex,  Pregnancy,  Age,  and  Temperament. 
The  composition  of  the  blood  is  also,  of  course,  much  influenced  by  diet. 

1.  Sex. — The  blood  of  men  differs  from  that  of  women,  chiefly  in 
being  of  somewhat  higher  specific  gravity,  from  its  containing  a  rela- 
tively larger  quantity  of  red  corpuscles. 

2.  Fret/nancy. — The  blood  of  pregnant  women  is  rather  lower  than 
the  average  specific  gravity,  from  deficiency  of  colored  corpuscles.  The 
quantity  of  the  uncolored  corpuscles,  on  the  other  hand,  and  of  fibrin,  is 
increased. 

3.  Age. — The  blood  of  the  foetus  is  very  rich  in  solid  matter,  and  es- 
pecially in  colored  corpuscles  ;  and  this  couditiou,  gradually  diminishing, 
continues  for  some  weeks  after  birth.  The  quantity  of  solid  matter  then 
falls  during  childhood  below  the  average,  rises  during  adult  life,  and  in 
old  age  falls  again. 

4.  Temperament. — There  appears  to  be  a  relatively  larger  quantity 
of  solid  matter,  and  particularly  of  colored  corpuscles,  in  those  of  a  ple- 
thoric or  sanguineous  temperament. 

5.  Diet. — Such  differences  in  the  composition  of  the  blood  as  are  due 


9U  HANDBOOK    OF    PHYSIOLOGY. 

to  the  temporary  presence  of  various  matters  absorbed  with  the  food  and 
drink,  as  well  as  the  more  lasting  changes  which  must  result  from  gener- 
ous or  poor  diet  respectively,  need  be  here  only  referred  to. 

6.  Effects  of  Bleeding. — The  result  of  bleeding  is  to  diminish  the 
specific  gravity  of  the  blood  ;  and  so  quickly,  that  in  a  single  venesection, 
the  portion  of  blood  last  drawn  has  often  a  less  specific  gravity  than  that 
of  the  blood  that  flowed  first.  This  is,  of  course,  due  to  absorption  of 
fluid  from  the  tissues  of  the  body.  [The  physiological  import  of  this 
fact,  namely,  the  instant  absorption  of  liquid  from  the  tissues,  is  the 
same  as  that  of  the  intense  thirst  which  is  so  common  after  either  loss  of 
blood,  or  the  abstraction  from  it  of  watery  fluid,  as  in  cholera,  diabetes, 
and  the  like.] 

For  some  little  time  after  bleeding,  the  want  of  colored  corpuscles  is 
well  marked,  but  with  this  exception,  no  considerable  alteration  seems  to 
be  produced  in  the  composition  of  the  blood  for  more  than  a  very  short 
time  ;  the  loss  of  the  other  constituents,  including  the  colored  corpuscles, 
being  very  quickly  repaired. 

Variations  in  different  parts  of  the  Body. — The  composition  of 
the  blood,  as  might  be  expected,  is  found  to  vary  in  different  parts  of 
the  body.  Thus  arterial  blood  differs  from  venous;  and  although  its 
composition  and  general  characters  are  uniform  throughout  the  whole 
course  of  the  systemic  arteries,  they  are  not  so  throughout  the  venous 
system — the  blood  contained  in  some  veins  differing  remarkably  from 
that  in  others. 

Differences  between  Arterial  and  Venous  Blood. — The  differences 
between  arterial  and  venous  blood  are  these: — 

(a.)  Arterial  blood  is  bright  red,  from  the  fact  that  almost  all  its 
haemoglobin  is  combined  with  oxygen  (Oxy-haemoglobin,  or  scarlet 
haemoglobin),  while  the  purple  tint  of  venous  blood  is  due  to  the  deoxi- 
dation  of  a  certain  quantity  of  its  oxy-haemoglobin,  and  its  consequent 
reduction  to  the  purple  variety  (Deoxidized,  or  purple  haemoglobin). 

(b.)  Arterial  blood  coagulates  somewhat  more  quickly. 

(c.)  Arterial  blood  contains  more  oxygen  than  venous,  and  less  car- 
bonic acid. 

Some  of  the  veins  contain  blood  which  differs  from  the  ordinary 
standard  considerably.  These  are  the  Portal,  the  Hepatic,  and  the 
Splenic  veins. 

Portal  vein. — The  blood  which  the  portal  vein  conveys  to  the  liver 
is  supplied  from  two  chief  sources;  namely,  from  the  gastric  and  mesen- 
teric veins,  which  contains  the  soluble  elements  of  food  absorbed  from 
the  stomach  and  intestines  during  digestion,  and  from  the  splenic  vein; 
it  must,  therefore,  combine  the  qualities  of  the  blood  from  each  of  these 
sources. 

The  blood  in  the  gastric  and  mesenteric  veins  will  vary  much  according 
to  the  stage  of  digestion  and  the  nature  of  the  food  taken,  and  can 
therefore  be  seldom  exactly  the  same.  Speaking  generally,  and  without 
considering  the  sugar,  and  other  soluble  matters  which  may  have  been 


THE    BLOOD.  91 

absorbed  from  the  alimentary  canal,  this  blood  appears  to  be  deficient  in 
solid  matters,  especially  in  colored  corpuscles,  owing  to  dilution  by  the 
quantity  of  water  absorbed,  to  contain  an  excess  of  proteid  matter,  and 
to  yield  a  less  tenacious  kind  of  fibrin  than  that  of  blood  generally. 

The  blood  from  the  splenic  vein  is  generally  deficient  in  colored  cor- 
puscles, and  contains  an  unusually  large  proportion  of  proteids.  The 
fibrin  obtainable  from  the  blood  seems  to  vary  in  relative  amount,  but 
to  be  almost  always  above  the  average.  The  proportion  of  colorless 
corpuscles  is  also  unusually  large.  The  whole  quantity  of  solid  matter 
is  decreased,  the  diminution  appearing  to  be  of  colored  corpuscles. 

The  blood  of  the  portal  vein,  combining  the  peculiarities  of  its  two 
factors,  the  splenic  and  mesenteric  venous  blood,  is  usually  of  lower 
specific  gravity  than  blood  generally,  is  more  watery,  contains  fewer 
colored  corpuscles,  more  proteids,  and  yields  a  less  firm  clot  than  that 
yielded  by  other  blood,  owing  to  the  deficient  tenacity  of  its  fibrin. 

Guarding  (by  ligature  of  the  portal  vein)  against  the  possibility  of  an 
error  in  the  analysis  from  regurgitation  of  hepatic  blood  into  the  portal 
vein,  recent  observers  have  determined  that  hepatic  venous  blood  contains 
less  water,  proteids,  and  salts  than  the  blood  of  the  portal  vein;  but  that 
it  yields  a  much  larger  amount  of  extractive  matter,  in  which  is  one 
constant  element,  namely,  grape-sugar,  which  is  found,  whether  saccha- 
rine or  farinaceous  matter  have  been  present  in  the  food  or  not. 

Development  of  the  Blood-Corpuscles. 

The  first  formed  blood-corpuscles  of  the  human  embryo  differ  much 
in  their  general  characters  from  those  which  belong  to  the  later  periods 


Fig.  83.— Part  of  the  network  of  developing  blood-vessels  in  the  vascular  area  of  a  guinea-pig. 
6i,  blood-corpuscles  becoming  free  in  an  ealarged  and  hollowed  out  part  of  the  network  ;  a.  process 
of  protoplasm.    (E.  A.  Schufer.) 

of  intra-uterine,  and  to  all  periods  of  extra-uterine  life.     Their  manner 
of  origin  is  at  first  very  simple. 

Surrounding  the  early  embryo  is  a  circular  area,  called  the  vascular 
area,  in  which  the  first  rudiments  of  the  blood-vessels  and  blood-corpus- 
cles are  developed.  Here  the  nucleated  embryonal  cells  of  the  mesoblast, 
from  which  the  blood-vessels  and  corpuscles  are  to  be  formed,  send  out 
processes  in  various  directions,  and  these  joining  together,  form  an  irreg- 


92 


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ular  meshwork.  The  nuclei  increase  in  number,  and  collect  chiefly  in 
the  larger  masses  of  protoplasm,  but  partly  also  in  the  processes.  These 
nuclei  gather  around  them  a  certain  amount  of  the  protoplasm,  and  be- 
coming colored,  form  the  red  blood-corpuscles.  The  protoplasm  of  the 
cells  and  their  branched  network  in  which  these  corpuscles  lie  then  be- 
come hollowed  out  into  a  system  of  canals  inclosing  fluid,  in  which  the 
red  nucleated  corpuscles  float.  The  corpuscles  at  first  are  from  about 
3g100  to  x^Vtf  °f  an  iQcn  in  diameter,  mostly  spherical,  and  with  granular 
contents,  and  a  well-marked  nucleus.  Their  nuclei,  which  are  about 
-%-^^q  of  an  inch  in  diameter,  are  central,  circular,  very  little  prominent 
on  the  surfaces  of  the  corpuscle,  and  apparently  slightly  granular  or 
tuberculated. 

The  corpuscles  then  strongly  resemble  the  colorless  corpuscles  of  the 
fully  developed  blood,  but  are  colored.  They  are  capable  of  amoeboid 
movement  and  multiply  by  division. 

When,  in  the  progress  of  embryonic  development,  the  liver  begins  to 
be  formed,  the  multiplication  of  blood-cells  in  the  whole  mass  of  blood 
ceases,  and  new  blood-cells  are  produced  by  this  organ,  and  also  by  the 
lymphatic  glands,  thymus  and  spleen.  These  are  at  first  colorless  and 
nucleated,  but  afterwards  acquire  the  ordinary  blood-tinge,  and  resemble 
very  much  those  of  the  first  set.  They  also  multiply  by  division.  In 
whichever  way  produced,  however,  whether  from  the  original  formative 
cells  of  the  embryo,  or  by  the  liver  and  the  other  organs  mentioned 
above,  these  colored  nucleated  cells  begin  very  early  in  foetal  life  to  be 
mingled  with  colored  wow- nucleated  corpuscles  resembling  those  of  the 
adult,  and  at  about  the  fourth  or  fifth  month  of  embryonic  existence  are 
completely  replaced  by  them. 

Origin  of  the  Mature  Colored  Corpuscles. — The  non-nucleated 
red  corpuscles  may  possibly  be  derived  from  the  nucleated,  but  in  all 
probability  are  an  entirely  new  formation,  and  the  methods  of  their  ori- 


Fig.  84.—  Development  of  red  corpuscles  in  connective-tissue  cells.  From  the  subcutaneous 
tissue  of  a  new-born  rat.  h,  a  cell  containing  haemoglobin  in  a  diffused  form  in  the  protoplasm  ;  h\ 
one  containing  colored  globules  of  varying  size  and  vacuoles  ;  h",  a  cell  filled  with  colored  globules 
of  nearly  uniform  size  ;  /,  /',  developing  fat  cells.    (E.  A.  Sehafer.) 

gin  are  the  following  : — (1.)  During  fcetal  life  and  possibly  in  some  ani- 
mals, e.g.,  the  rat,  which  are  born  in  an  immature  condition,  for  some 
little  time  after  birth,  the  blood  discs  arise  in  the  connective-tissue  cells 


THE   BLOOD.  93 

in  the  following  way.  Small  globules,  of  varying  size,  of  coloring 
matter  arise  in  the  protoplasm  of  the  cells,  and  the  cells  themselves  be- 
come branched,  their  branches  joining  the  branches  of  similar  cells. 
The  cells  next  become  vacuolated,  and  the  red  globules  are  free  in  a 
cavity  filled  with  fluid  (Fig.  85)  ;  by  the  extension  of  the  cavity  of  the 
cells  into  their  processes  anastomosing  vessels  are  produced,  which  ulti- 
mately join  with  the  previously  existing  vessels,  and  the  globules,  now 
having  the  size  and  appearance  of  the  ordinary  red  corpuscles,  are  passed 
into  the  general  circulation.  This  method  of  formation  is  called  intra- 
cellular (Schafer). 

(2.)  From  the  white  corpuscles. — The  belief  that  the  red  corpuscles 
are  derived  from  the  white  is  still  very  general,  although  no  new  evidence 
has  been  recently  advanced  in  favor  of  this  view.  It  is,  however,  uncer- 
tain whether  the  nucleus  of  the  white  corpuscle  becomes  the  red  cor- 
puscle, or  whether  the  whole  white  corpuscle  is  bodily  converted  into  the 
red  by  the  gradual  clearing  up  of  its  contents  with  a  disappearance  of 
the  nucleus.     Probably  the  latter  view  is  the  correct  one. 

(3.)  From  the  medulla  of  bones. — Colored  corpuscles  are  to  a  very  large 
extent  derived  during  adult  life  from  the  large  pale  cells  in  the  red  mar- 
row of  bones,  especially  of  the  ribs  (Figs.  S3,  84).  These  cells  become 
colored  from  the  formation  of  haemoglobin  chiefly  in  oue  part  of  their 
protoplasm.  This  colored  part  becomes  separated  from  the  rest  of  the 
cell  and  forms  a  red  corpuscle,  being  at  first  cup-shaped,  but  soon  taking 
on  the  normal  appearance  of  the  mature  corpuscle.  It  is  supposed  that 
the  protoplasm  may  grow  up  again  and  form  a  number  of  red  corpuscles 
in  a  similar  way. 

(4.)  From  the  tissue  of  the  spleen. — It  is  probable  that  colored  as  well 
as  colorless  corpuscles  may  be  produced  in  the  spleen. 

(5.)  From  Microcytes. — Hay  em  describes  the  small  particles  (micro- 
cytes),  previously  mentioned  as  contained  in  the  blood  (p.  71),  and  which 
he  calls  haematoblasts,  as  the  precursors  of  the  red  corpuscles.  They  ac- 
quire color,  and  enlarge  to  the  normal  size  of  red  corpuscles. 

Without  doubt,  the  red  corpuscles  have,  like  all  other  parts  of  the 
organism,  a  tolerably  definite  term  of  existence,  and  in  a  like  manner 
die  and  waste  away  when  the  portion  of  work  allotted  to  them  has  been 
performed.  Neither  the  length  of  their  life,  however,  nor  the  fashion 
of  their  decay  has  been  yet  clearly  made  out.  It  is  generally  believed 
that  a  certain  number  of  the  colored  corpuscles  undergo  disintegration 
in  the  spleen  ;  and  indeed  corpuscles  in  various  degrees  of  degeneration 
have  been  observed  in  that  organ. 

Origin  of  the  Colorless  Corpuscles. — The  colorless  corpuscles  of 
the  blood  are  derived  from  the  lymph  corpuscles,  being,  indeed,  indis- 
tinguishable from  them  ;  and  these  come  chiefly  from  the  lymphatic 
glands.     Their  number  is  increased  by  division. 


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HANDBOOK    OF    PHYSIOLOGY. 


Colorless  corpuscles  are  also  in  all  probability  derived  from  the  spieen 
and  thymus,  and  also  from  the  germinating  endothelium  of  serous  mem- 


FI(*-  85- —Further  development  of  blood-corpuscles  in  connective-tissue  cells  and  transformation 
of  the  latter  into  capillary  blood-vessels,  a,  an  elongated  cell  with  a  cavity  in  the  protoplasm  oc- 
cupied by  fluid  and  by  blood -corpuscles  which  are  still  globular;  b,  a  hollow  cell,  the  nucleus  of 
which  has  multiplied.  The  new  nuclei  are  arranged  around  the  wall  of  the  cavity,  the  corpuscles 
in  which  have  now  become  discoid;  c,  shows  the  mode  of  union  of  a  "  hsemapoietic  "  cell,  which  in 
this  instance  contains  only  one  corpuscle,  with  the  prolongation  (bt)  of  a  previously  existing  vessel; 
a  and  c,  from  the  new-born  rat;  b,  from  the  foetal  sheep.    (E.  A.  Schafer.) 

branes,  and  from  connective  tissue.     The  corpuscles  are  carried  into  the 
blood  either  with  the  lymph  and  chyle,  or  pass  directly  from  the  lym- 


Fig.  86.— Colored  nucleated  corpuscles,  from  the  red  marrow  of  the  guinea-pig.    (E.  A.  Schufer.) 

phatic  tissue  in  which  they  have  been  formed  into  the  neighboring 
blood-vessels. 

1.  Uses  of  the  Blood.— -To  be  a  medium  for  the  reception  and 
storing  of  matter  (ordinary  food,  drink,  and  oxygen)  from  the  outer 
world,  and  for  its  conveyance  to  all  parts  of  the  body. 

2.  To  be  a  source  whence  the  various  tissues  of  the  body  may  take 
the  materials  necessary  for  their  nutrition  and  maintenance  ;  and  whence 
the  secreting  organs  may  take  the  constituents  of  their  various  secretions. 

3.  To  be  a  medium  for  the  absorption  of  refuse  matters  from  all  the 
tissues,  and  for  their  conveyance  to  those  organs  whose  function  it  is  to 
separate  them  and  cast  them  out  of  the  body. 

4.  To  warm  and  moisten  all  parts  of  the  body. 


CHAPTER  IV. 

THE   CIRCULATION   OF  THE   BLOOD. 

The  Heart  is  a  hollow  muscular  organ  consisting  of  four  chambers, 
two  auricles  and  two  ventricles,  arranged  in  pairs.  On  the  right  and 
left  sides  of  the  heart  is  an  auricle  joined  to  and  communicating  with  a 
ventricle,  but  the  chambers  on  the  right  side  do  not  directly  communi- 
cate with  those  on  the  left  side.     The  circulation  of  the  blood  is  chiefly 


Fig.  87.— Diagram  of  the  circulation.— The  unshaded  part  of  the  figure  to  the  right  indicates 
the  district  of  the  circulation  of  arterial  blood;  the  dark  part  to  the  left  the  district  of  venous  blood. 

carried  on  by  the  contraction  or  systole  of  the  muscular  walls  of  the 
chambers  of  the  heart :  the  auricles  contracting  simultaneously,  and 
their  contraction  being  followed  by  the  simultaneous  contraction  of  the 
ventricles.  The  blood  is  conveyed  away  from  the  left  side  of  the  heart 
(as  in  the  diagram,  Fig.  87)  by  the  arteries,  and  returned  to  the  right 


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side  of  the  heart  by  the  veins,  the  arteries  and  veins  being  continuous 
with  each  other  at  one  end  by  means  of  the  heart,  and  at  the  other  by  a 
fine  network  of  vessels  called  the  capillaries.  The  blood,  therefore,  in 
its  passage  from  the  heart  passes  first  into  the  arteries,  then  into  the  ca- 
pillaries, and  lastly  into  the  veins,  by  which  it  is  conveyed  back  again  to 
the  heart,  thus  completing  a  revolution  or  circulation. 

As  the  right  side  of  the  heart,  however,  does  not  directly  communi- 
cate with  the  left,  in  order  to  complete  the  circulation  it  is  necessary 
that  the  blood  should  pass  from  the  right  side  to  the  lungs,  through  the 
pulmonary  artery,  then  through  the  pulmonary  capillary-vessels,  and 
through  the  pulmonary  veins  to  the  left  side  of  the  heart  (Fig.  87). 
Thus  there  are  two  circulations  by  which  the  blood  must  pass  ;  the  one,, 


Right 
Lung 


Pulmonary 
Artery. 


-    Left 
!l   Lung. 


Diaphragm. 

Fig  88.  —View  of  heart  and  lungs  in  situ.  The  front  portion  of  the  chest- wall,  and  the  outer  or 
parietal  layers  of  the  pleurae  and  pericardium  have  been  removed.  The  lungs  are  partly  col- 
lapsed. 

a  shorter  circuit  from  the  right  side  of  the  heart  to  the  lungs  and  back 
again  to  the  left  side  of  the  heart ;  the  other  and  larger  circuit,  from 
the  left  side  of  the  heart  to  all  parts  of  the  body  and  back  again  to  the 
right  side  ;  but  more  strictly  speaking,  there  is  only  one  complete  circu- 
ation,  which  may  be  diagrammatically  represented  by  a  double  loop,  as 
in  the  accompanying  figure  (Fig.  8T). 

On  reference  to  this  figure,  and  noticing  the  direction  of  the  arrows, 
which  represent  the  course  of  the  stream  of  blood,  it  will  be  observed 
that  while  there  is  a  smaller  and  a  larger  circle,  both  of  which  pass 
through  the  heart,  yet  that  these  are  not  distinct,  one  from  the  other, 
but  are  formed  really  by  one  continuous  stream,  the  whole  of  which 
must,  at  one  part  of  its  course,  pass  through  the  lungs.  Subordinate  to 
the  two  principal  circulations,  the  Pulmonary  and  Systemic,  as  they  are 


THE    CIRCULATION    OF    THE    BLOOD.  9  i 

named,  it  will  be  noticed  also  in  the  same  figure  that  there  is  another, 
by  which  a  portion  of  the  .stream  of  hloocl  having  been  diverted  once 
into  the  capillaries  of  the  intestinal  canal,  and  some  other  organs,  and 
o-athered  up  again  into  a  single  stream,  is  a  second  time  divided  in  its 
passage  through  the  liver,  before  it  finally  reaches  the  heart  and  com- 
pletes a  revolution.  This  subordinate  stream  through  the  liver  is  called 
the  Portal  circulation. 

As  a  necessary  step  towards  the  consideration  of  the  method  by  which 
the  circulation  is  maintained,  it  will  be  advisable  in  the  first  place  to  de- 
vote some  time  to  the  description  of  various  important  points  in  the 
anatomy  and  minute  structure  of — I.  The  Heart;  II.  The  Arteries; 
III.  The  Capillaries;  IV.  The  Veins.  We  shall  then  be  in  a  better  po- 
sition to  discuss  the  problems  in  the  physiology  of  the  circulation. 

(I.)  The  Heart. 

The  heart  is  contained  in  the  chest  or  thorax,  and  lies  between  the 
right  and  left  lungs  (Fig.  88),  enclosed  in  a  membranous  sac — the  peri- 
cardium, which  is  made  up  of  two  distinct  parts,  an  external  fibrous 
membrane,  composed  of  closely  interlacing  fibres,  which  has  its  base  at- 
tached to  the  diaphragm  or  midriff,  the  great  muscle  which  forms  the 
floor  of  the  chest  and  divides  it  from  the  abdomen — both  to  the  central 
tendon  and  to  the  adjoining  muscular  fibres,  while  the  smaller  and  upper 
end  is  lost  on  the  large  blood-vessels  by  mingling  its  fibres  with  that  of 
their  external  coats;  and  an  internal  serous  layer,  which  not  only  lines 
the  fibrous  sac,  but  also  is  reflected  on  to  the  heart,  which  it  completely 
invests.  The  part  which  lines  the  fibrous  membrane  is  called  the  parietal 
layer,  and  that  enclosing  the  heart,  the  visceral  layer,  and  these  being 
continuous  for  a  short  distance  along  the  great  vessels  of  the  base  of  the 
heart,  form  a  closed  sac,  the  cavity  of  which  in  health  contains  just 
enough  fluid  to  lubricate  the  two  surfaces,  and  thus  enable  them  to  glide 
smoothly  over  each  other  during  the  movements  of  the  heart.  Most  of 
the  vessels  passing  in  and  out  of  the  heart  receive  more  or  less  invest- 
ment from  this  sac. 

The  heart  in  the  chest  is  situated  behind  the  sternum  and  costal  car- 
tilages, being  placed  obliquely  from  right  to  left,  quite  two-thirds  to  the 
left  of  the  mid-sternal  line.  It  is  of  pyramidal  shape,  with  the  apex 
pointing  downwards,  outwards,  and  towards  the  left,  and  the  base  back- 
wards, inwards,  and  towards  the  right.  It  rests  upon  the  diaphragm, 
and  its  pointed  apex,  formed  exclusively  of  the  left  side  of  the  heart,  is  in 
contact  with  the  chest  wall,  and  during  life  beats  against  it  at  a  point 
called  the  apex  beat,  situated  in  the  fifth  intercostal  space,  about  two 
inches  below  the  left  nipple,  and  an  inch  aud  a  half  to  the  sternal  side. 
The  heart  is  suspended  in  the  chest  by  the  large  vessels  which  proceed 


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HANDBOOK    OF    PHYSIOLOGY. 


from  its  base,  but,  excepting  the  base,  the  organ  itself  lies  free  in  the 
sac  of  the  pericardium.  The  part  which  rests  upon  the  diaphragm  is 
flattened,  and  is  known  as  the  posterior  surface,  whilst  the  free  upper 
part  is  called  the  anterior  surface.  The  margin  towards  the  left  is 
thick  and  obtuse,  whilst  the  lower  margin  towards  the  right  is  thin  and 
acute. 

On  examination  of  the  external  surface  the  division  of  the  heart  into 
parts  which  correspond  to  the  chambers  inside  of  it  may  be  traced,  for 
a  deep  transverse  groove  called    the  auriciilo-ventricidar  groove  divides 


Fig.  89.— The  right  auricle  and  ventricle  opened,  aud  a  part  of  their  right  and  anterior  walls 
removed,  so  as  to  show  their  interior.  y>.—\,  superior  vena  cava;  2,  inferior  vena  cava;  2',  he- 
patic veins  cut  short;  3,  right  auricle ;  3',  placed  in  the  fossa  ovalis,  below  which  is  the  Eustachian 
valve;  3",  is  placed  close  to  the  Hperture  of  the  coronary  vein ;  +, +,  placed  in  the  auriculo-ven- 
tricular  groove,  where  a  narrow  portion  of  the  adjacent  walls  of  the  auricle  and  ventricle  has  been 
preserved;  4,  4,  cavity  of  the  right  ventricle,  the  upper  figure  is  immediately  below  the  semilunar 
valves;  4',  large  columna  carnea  or  musculus  papillaris;  5,  5',  5",  tricuspid  valve;  6,  placed  in  the 
interior  of  the  pulmonary  artery,  a  part  of  the  anterior  wall  of  that  vessel  having  been  removed, 
and  a  narrow  portion  of  it  preserved  at  its  commencement,  where  the  semilunar  valves  are  attached ; 
7,  concavity  of  the  aortic  arch  close  to  the  cord  of  the  ductus  arteriosus;  8,  ascending  part  or  sinus  of 
the  arch  covered  at  its  commencement  by  the  auricular  appendix  and  pulmonary  artery;  9,  placed 
between  the  innominate  and  left  carotid  arteries;  10,  appendix  of  the  left  auricle;  11,  11,  the  outside 
of  the  left  ventricle,  the  lower  figure  near  the  apex.    (Allen  Thomson.) 

the  auricles  which  form  the  base  of  the  heart  from  the  ventricles  which 
form  the  remainder,  including  the  apex,  the  ventricular  portion  being  by 
far  the  greater;  aad,  again,  the  inter -ventricular  groove  runs  between 


THK    CIRCULATION    OF    T3E    BLOOD.  'J'.t 

the  ventricles  both  front  and  back,  and  separates  the  one  from  the  other. 
The  anterior  groove  is  nearer  the  left  margin  and  the  posterior  nearer 
the  right,  as  the  front  surface  of  the  heart  is  made  up  chiefly  of  the 
right  ventricle  and  the  posterior  surface  of  the  left  ventricle.  In  the 
furrows  run  the  coronary  vessels,  which  supply  the  tissue  of  the  heart 
with  blood,  as  well  as  nerves  and  lymphatics  imbedded  in  more  or  less 
fatty  material. 

The  Chambers  of  the  Heart. — The  interior  of  the  heart  is  divided  by 
a  partition  in  such  a  manner  as  to  form  two  chief  chambers  or  cavities 
— right  and  left.  Each  of  these  chambers  is  again  subdivided  into  an 
upper  and  a  lower  portion,  called  respective^,  as  already  incidentally 
mentioned,  auricle  and  ventricle,  which  freely  communicate  one  with 
the  other;  the  aperture  of  communication,  however,  is  guarded  by  valves, 
so  disposed  as  to  allow  blood  to  pass  freely  from  the  auricle  into  the  ven- 
tricle, but  not  in  the  opposite  direction.  There  are  thus  four  cavities 
altogether  in  the  heart — the  auricle  and  ventricle  of  oue  side  being  quite 
separate  from  those  of  the  other  (Fig.  89). 

(1.)  Right  auricle. — The  right  auricle  is  situated  at  the  right  part 
of  the  base  of  the  heart  as  viewed  from  the  front.  It  is  a  thin-walled 
cavity  of  more  or  less  quadrilateral  shape,  prolonged  at  one  corner  into 
a  tongue-shaped  portion,  the  right  auricular  appendix,  which  slightly 
overlaps  the  exit  of  the  great  artery,  the  aorta,  from  the  heart. 

The  interior  is  smooth,  being  lined  with  the  general  lining  of  the 
heart,  the  endocardium,  and  into  it  open  the  superior  and  inferior  venae 
cavae,  or  great  veins,  which  convey  the  blood  from  all  parts  of  the  body 
to  the  heart.  The  former  is  directed  downwards  and  forwards,  the  latter 
upwards  and  inwards;  between  the  entrances  of  these  vessels  is  a  slight 
tubercle  called  tubercle  of  Lower.  The  opening  of  the  inferior  cava  is 
protected  and  partly  covered  by  a  membrane  called  the  Eustachian  valve. 
Tu  the  posterior  wall  of  the  auricle  is  a  slight  depression  called  the  fossa 
avails  which  corresponds  to  an  openiug  between  the  right  and  left  auricles 
which  exists  in  fcetal  life.  The  right  auricular  appendix  is  of  oval  form, 
and  admits  three  fingers.  Various  veins,  including  the  coronary  sinus, 
or  the  dilated  portion  of  the  right  coronary  vein,  open  into  this  chamber. 
In  the  appendix  are  closely  set  elevations  of  the  muscular  tissue  covered 
with  endocardium,  and  on  the  anterior  wall  of  the  auricle  are  similar 
elevations  arranged  parallel  to  one  another,  called  musculi pectinati. 

(2.)  Right  Ventricle. — The  right  ventricle  occupies  the  chief  part 
of  the  anterior  surface  of  the  heart,  as  well  as  a  small  part  of  the  poste- 
rior surface  :  it  forms  the  right  margin  of  the  heart.  It  takes  no  part 
in  the  formation  of  the  apex.  On  section  its  cavity,  in  consequence  of 
the  encroachment  upon  it  of  the  septum  ventriculorum,  in  semilunar  or 
crescentic  (Fig.  91)  ;  into  it  are  two  openings,  the  auriculo-ventricular 
at  the  base,  and  the  opening  of  the  pulmonary  artery  also  at  the  base. 


100  HANDBOOK    OF    PHYSIOLOGY. 

but  more  to  the  left ;  the  part  of  the  ventricle  leading  to  it  is  called  the 
conus  arteriosus  or  infundibulum  ;  both  orifices  are  guarded  by  valves, 
the  former  called  tricuspid  and  the  latter  semilunar  or  sigmoid.  In  this 
ventricle  are  also  the  projections  of  the  muscular  tissue  called  columnce 
carnece  (described  at  length  p.  103). 

(3.)  Left  Auricle. — The  left  auricle  is  situated  at  the  left  and  poste- 
rior part  of  the  base  of  the  heart,  and  is  best  seen  from  behind.  It  is 
quadrilateral,  and  receives  on  either  side  two  pulmonary  veins.  The 
auricular  appendix  is  the  only  part  of  the  auricle  seen  from  the  front, 
and  corresponds  with  that  on  the  right  side,  but  is  thicker,  and  the  in- 
terior is  more  smooth.  The  left  auricle  is  only  slightly  thicker  than  the 
right,  the  difference  being  as  1%  lines  to  1  line.  The  left  auriculo-ven- 
tricular  orifice  is  oval,  and  a  little  smaller  than  that  on  the  right  side  of 
the  heart.  There  is  a  slight  vestige  of  the  foramen  between  the  auri- 
cles, which  exists  in  foetal  life,  on  the  septum  between  them. 

(4.)  Left  Ventricle. — Though  taking  part  to  a  comparatively  slight 
extent  in  the  anterior  surface,  the  left  ventricle  occupies  the  chief  part 
of  the  posterior  surface.  In  it  are  two  openings  very  close  together, 
viz.,  the  auriculo-ventricular  and  the  aortic,  guarded  by  the  valves  cor- 
responding to  those  of  the  right  side  of  the  heart,  viz.,  the  bicuspid  or 
mitral  and  the  semilunar  or  sigmoid.  The  first  opening  is  at  the  left 
and  back  part  of  the  base  of  the  ventricle,  and  the  aortic  in  front  and 
towards  the  right.  In  this  ventricle,  as  in  the  right,  are  the  columns 
carneas,  which  are  smaller  but  more  closely  reticulated.  They  are  chiefly 
found  near  the  apex  and  along  the  posterior  wall.  They  will  be  again 
referred  to  in  the  description  of  the  valves.  The  walls  of  the  left  ven- 
tricle, which  are  nearly  half  an  inch  in  thickness,  are,  with  the  excep- 
tion of  the  apex,  twice  or  three  times  as  thick  as  those  of  the  right. 

Capacity  of  the  Chambers. — The  capacity  of  the  two  ventricles  is 
about  four  to  six  ounces  of  blood,  the  whole  of  which  is  impelled  into 
their  respective  arteries  at  each  contraction.  The  capacity  of  the  auri- 
cles is  rather  less  than  that  of  the  ventricles  :  the  thickness  of  their 
walls  is  considerably  less.  The  latter  is  adapted  to  the  small  amount  of 
force  which  the  auricles  require  in  order  to  empty  themselves  into  their 
adjoining  ventricles  ;  the  former  to  the  circumstance  of  the  ventricles 
being  partly  filled  with  the  blood  before  the  auricles  contract. 

Size  and  Weight  of  the  Heart. — The  heart  is  about  5  inches  long,  3| 
inches  greatest  width,  and  2£  inches  in  its  extreme  thickness.  The 
average  weight  of  the  heart  in  the  adult  is  from  9  to  10  ounces ;  its 
weight  gradually  increasing  throughout  life  till  middle  age  ;  it  dimin- 
ishes in  old  age. 

Structure. — The  walls  of  the  heart  are  constructed  almost  entirely  of 
layers  of  muscular  fibres  ;  but  a  ring  of  connective  tissue,  to  which  some 
of  the  muscular  fibres  are  attached,  is  inserted  between  each  auricle  and 


THE  CIKCILLATION    OF    T1IK    UU>oI>. 


101 


ventricle,  and  forms  the  boundary  of  the  auriculo-ventricular  opening. 

Fibrous  tissue  also  exists  at  the  origins  of  the  pulmonary  artery  and 
aorta. 

The  muscular  fibres  of  each  auricle  are  in  part  continuous  with  those 
of  the  other,  and  partly  separate  ;  and  the  same  remark  holds  true  for 
the  ventricles.  The  fibres  of  the  auricles  are,  however,  quite  separate 
from  those  of  the  ventricles,  the  bond  of  connection  between  them  be- 
ing only  the  fibrous  tissue  of  the  auriculo-ventricular  openings. 


Fig.  90.-The  left auricle  and  ventricle  opened  and  a  part  of  their  anterior  and  left  walls  re- 
moved, ji.  —The  pulmonary  artery  has  been  divided  al  its  commencement;  the  opening:  into  the 
left  ventricle  is  carried  a  short  distance  into  the  aorta  between  two  of  the  segments  of  the  semi- 
lunar valves;  and  the  left  part  of  the  auricle  with  its  appendix  lias  been  removed.  The  right  auri- 
cle is  out  of  view.  I.  t  lie  two  right  pulmonary  v. -ins  cut  short :  their  openings  are  seen  wil  bin  the 
auricle:  1',  placed,  within  the  cavity  of  the  auricle  on  the  left  side  of  the  septum  and  on  the  part 
which  forms  the  remains  uf  tlr' valve  of  tl»e  foramen  ovale,  of  which  the  creBcentic  fold  is  seen 
towards  the  left  hand  of  r :  2,  a  narrow  portion  of  the  wall  of  the  auricle  and  ventricle  preserve,  i 
round  the  auriculo-ventricular  orifice;  8,  8',  the  cut  surface  of  the  walls  of  the  ventricle,  seen  to  be 
come  very  much  thinner  towards  3",  at  the  apex;  4,  a  small  part  of  the  anterior  wall  of  the  left 
ventricle  which  has  been  preserved  with  the  principal  anterior  columns  carnea  or  mnsculous  papil 
laris  attached  to  it;  5,  r>.  musculi  papillaris;  :">',  the  left  side  of  the  septum,  between  the  two  ventri 
cles,  within  the  cavity  of  the  left  ventricle;  6,8',  the  mitral  valve;  7.  placed  in  the  interior  of  the 
aorta  near  its  commencement  and  above  the  three  segments  of  its  semilunar  valve  which  are  hang- 
ing loosely  together;  7',  the  exterior  of  the  great  aorac  sinus;  8,  the  root  of  the  pulmonary  artery 
and  its  semilunar  valves;  s  ,  tin-  separated  portion  Of  the  pulmonary  artery  remaining  attached  to 
the  aorta  by  9,  the  cord  of  the  ductus  arteriosus;  10,  the  arteries  rising  from  the  summit  of  the 
aortic  arch!    (Allen  Thomson.) 


102 


HANDBOOK    OF    PHTSIOLOGT. 


The  muscular  fibres  of  the  heart,  unlike  those  of  most  of  the  invol- 
untary muscles,  are  striated  ;  hut  although,  in  this  respect,  they  re- 
semble the  skeletal  muscles,  they  have  distinguishing  characteristics  of 

their  own.  The  fibres  which  lie  side  by 
side  are  united  afc  frequent  intervals 
by  short  branches  (Fig.  92).  The  fibres 
are  smaller  than  those  of  the  ordinary 
striated  muscles,  and  their  striation  is 
less  marked.  No  sarcolemma  can  be 
discerned.  The  muscle-corpuscles  are 
situate  in  the  middle  of  the  substance 
of  the  fibre  ;  and  in  correspondence 
with  these  the  fibres  appear  under  cer- 
tain conditions  subdivided  into  oblong 
portions  or  "cells,"  the  offsets  from 
which  are  the  means  bv  which  the  fibres  anastomose  one  with  another 
(Fig.  93). 

Endocardium.— As  the  heart  is  clothed  on  the  outside  by  a  thin 
transparent  layer  of  pericardium,  so  its  cavities  are  lined  by  a  smooth 
and  shining  membrane,  or  endocardium,  which  is  directly  continuous 


Fig.  91. — Transverse  section  of  bul- 
lock's heart  in  a  state  of  cadaveric  rigid- 
ity, a,  cavity  of  left  ventricle,  b,  cavity  of 
right  ventricle .    (Da  It  on  J 


Fig.  92.  Fig.  93. 

Fin.  92.— Network  of  muscular  fibres  (striated)  from  the  heart  of  a  pig.    The  nuclei  of  the 
muscle-corpuscles  are  well  shown,     x  450.     (Klein  and  Noble  Smith.; 
Fig.  93.— Muscular  fibre  cells  from  the  heart.     (.E.A.  SchaferO 


with  the  internal  lining  of  the  arteries  and  veins.  The  endocardium  is 
composed  of  connective  tissue  with  a  large  admixture  of  elastic  fibres  ; 
and  on  its  inner  surface  is  laid  down  a  single  tesselated  layer  of  flattened 


THE   OIBOULATION    OF   THE    BLOOD.  108 

endothelial  cells.  Here  and  there  unstriped  muscular  fibres  are  some- 
times found  in  the  tissue  of  the  endocardium. 

Valves  of  the  Heart. — The  arrangement  of  the  heart's  valves  is 
such  that  the  blood  can  pas.s  only  in  one  directioii  (Fig.  94). 

The  tricuspid  valve  (5,  Fig.  89)  presents  three  principal  cusps  or 
subdivisions,  and  mitral  or  bicuspid  valve,  because  it  has  two  such  por- 
tions (6,  Fig.  90).  But  in  both  valves  there  is  between  each  two  prin- 
cipal portions  a  smaller  one  ;  so  that  more  properly,  the  tricuspid  may 
be  described  as  consisting  of  six,  and  the  mitral  of  four,  portions.  Each 
portion  is  of  triangular  form,  its  base  is  continuous  with  the  bases  of  the 
neighboring  portions,  so  as  to  form  an  annular  membrane  around  the 
auriculo-ventricular  opening,  and  is  fixed  to  a  tendinous  ring  which  en- 


Fig.  94.— Diagram  of  the  circulation  through  the  heart  (Daltou  i. 

circles  the  orifice  between  the  auricle  and  ventricle  and  receives  the 
insertions  of  the  muscular  fibres  of  both.  In  each  principal  cusp  may 
be  distinguished  a  central  part,  extending  from  base  to  apex,  and  includ- 
ing about  half  its  width.  It  is  thicker,  and  much  tougher  than  the 
border-pieces  or  edges. 

While  the  bases  of  the  cusps  of  the  valves  are  fixed  to  the  tendinous 
rings,  their  ventricular  surface  and  borders  are  fastened  by  slender  ten- 
dinous fibres,  the  chordae  tendinem,  to  the  internal  surface  walls  of  the 
ventricles,  the  muscular  fibres  of  which  project  into  the  ventricular  cavity 
in  the  form  of  bundles  or  columns — the  columna  car  mm.  These  columns 
are  not  all  alike,  for  while  sonic  are  attached  along  their  whole  length 
on  one  side,  and  by  their  extremities,  others  arc  attached  onlv  by  their 


104  HANDBOOK    OF    PHYSIOLOGY. 

extremities  ;  and  a  third  set,  to  which  the  name  musculi  papillares  has 
been  given,  are  attached  to  the  wall  of  the  ventricle  by  one  extremity 
only,  the  other  projecting,  papilla-like,  into  the  cavity  of  the  ventricle 
(5,  Fig.  89),  and  having  attached  to  it  chordae  tendineae.  Of  the  tendi- 
nous chords,  besides  those  which  pass  from  the  walls  of  the  ventricle 
and  the  musculi  papillares  to  the  margins  of  the  valves,  there  are  some 
of  especial  strength,  which  pass  from  the  same  parts  to  the  edges  of  the 
middle  and  thicker  portions  of  the  cusps  before  referred  to.  The  ends 
of  these  cords  are  spread  out  in  the  substance  of  the  valve,  giving  its 
middle  piece  its  peculiar  strength  and  toughness  ;  and  from  the  sides 
numerous  other  more  slender  and  branching  cords  are  given  off,  which 
are  attached  all  over  the  veutricular  surface  of  the  adjacent  border- 
pieces  of  the  principal  portions  of  the  valves,  as  well  as  to  those  smaller 
portions  which  have  been  mentioned  as  lying  between  each  two  princi- 
pal ones.  Moreover,  the  musculi  papillares  are  so  placed  that,  from  the 
summit  of  each,  tendinous  cords  proceed  to  the  adjacent  halves  of  two 
of  the  principal  divisions,  and  to  one  intermediate  or  smaller  division,  of 
the  valve. 

The  preceding  description  applies  equally  to  the  mitral  and  tricuspid 
valve  ;  but  it  should  be  added  that  the  mitral  is  considerably  thicker 
and  stronger  than  the  tricuspid,  in  accordance  with  the  greater  force 
which  it  is  called  upon  to  resist. 

The  semilunar  valves,  three  in  number,  guard  the  orifices  of  the  pul- 
monary artery  and  of  the  aorta.  They  are  nearly  alike  on  both  sides  of 
the  heart ;  but  the  aortic  valves  are  altogether  thicker  and  more  strongly 
constructed  than  the  pulmonary  valves,  in  accordance  with  the  greater 
pressure  which  they  have  to  withstand.  Each  valve  is  of  semilunar 
shape,  its  convex  margin  being  attached  to  a  fibrous  ring  at  the  place  of 
junction  of  the  artery  to  the  ventricle,  and  the  concave  or  nearly  straight 
border  being  free,  so  that  each  valve  forms  a  little  pouch  like  a  watch- 
pocket  (7,  Fig.  90).  In  the  centre  of  the  free  edge  of  the  valve,  which 
contains  a  fine  cord  of  fibrous  tissue,  is  a  small  fibrous  nodule,  the  cor- 
pus Arantii,  and  from  this  and  from  the  attached  border  fine  fibres  ex- 
tend into  every  part  of  the  mid  substance  of  the  valve,  except  a  small 
lunated  space  just  within  the  free  edge,  on  each  side  of  the  corptis  Aran- 
tii.  Here  the  valve  is  thinnest,  and  composed  of  little  more  than  the 
endocardium.  Thus  constructed  and  attached,  the  three  semilunar 
valves  are  placed  side  by  side  around  the  arterial  orifice  of  each  ventricle, 
so  as  to  form  three  little  pouches,  which  can  be  separated  by  the  blood 
passing  out  of  the  ventricle,  but  which  immediately  afterwards  are 
pressed  together  so  as  to  prevent  any  return  (7,  Fig.  89,  and  7,  Fig.  90). 
This  will  be  again  referred  to.  Opposite  each  of  the  semilunar  cusps, 
both  in  the  aorta  and  pulmonary  artery,  there  is  a  bulging  outwards  of 
the  wall  of  the  vessel  :  these  buMngrs  are  called  the  sinuses  of  Valsalva. 


THE    CIRCULATION    <>K  THE    lil.oon. 


H>; 


Structure  of  the  Valves. — The  valves  o.f  the  heart  are  formed  essen- 
tially of  thick  layers  of  closely  woven  connective  and  elastic  tissue,  over 
which,  on  every  part,  is  reflected  the  endocardium. 


If.     The  Arteries. 

Distribution. — The  arterial  system  begins  at  the  left  ventricle  in  a 
single  large  trunk,  the  aorta,  which  almost  immediately  after  its  origin 
gives  off  in  the  thorax  three  large  branches  for  the  supply  of  the  head, 
neck,  and  upper  extremities;  it  then  traverses  the  thorax  and  abdomen, 
giving  off  branches,  some  large  and  some  small,  for  the  supply  of  the 


pi  m 


Fig.  9(5. 

Fig.  96.— Minute  artery  viewed  in  longitudinal  section,  e.  Nucleated  endothelial  membrane, 
with  faint  nuclei  in  lumen," looked  at  from  above.  /'.  Thin  elastic  tunica  intima.  in.  Muscular  coat 
or  tunica  media.  a.  Tunica  adventitia.     (Klein  and  ^oble  Smith.)     X  250. 

Fig.  96.— Transverse  section  through  a  large  branch  of  the  interior  mesenteric  artery  of  a  pig. 
e,  endothelial  membrane  ;  i,  tunica  elastica  interna,  no  subendothelial  layer  is  te .-u  ;  m.  muscular 
tunica  media,  containing  only  a  few  wavy  elastic  fibres  :  e,  c,  tunica  elastica  externa,  dividing  the 
media  from  i he  connective-tissue  adventitia,  a.    (Klein and  Noble  Smith.)     X  350. 

various  organs  and  tissues  it  passes  on  its  way.  In  the  abdomen  it  di- 
vides into  two  chief  branches,  for  the  supply  of  the  lower  extremities. 
The  arterial  branches  wherever  given  off  divide  and  subdivide,  until  the 
calibre  of  each  subdivision  becomes  very  minute,  and  these  minute  ves- 
sels pass  into  capillaries.  Arteries  are,  as  a  rule,  placed  in  situations 
protected  from  pressure  and  other  dangers,  and  are,  with  few  exceptions, 
straight  in  their  course,  and  frequently  communicate  (anastomose  or  in- 
osculate) with  other  arteries.  The  blanches  are  usually  given  off  at  an 
acute  angle,  and  the  area  of  the  branches  of  an  artery  generally  exceeds 
that  of  the  parent  trunk;  and  as  the  distance  from  the  origin  is  increased, 
the  area  of  the  combined  branches  is  increased  also. 

After  death,  arteries  are  usually  found  dilated  (not  collapsed  as  the 
veins  are)  and  empty,  and  it  was  to  this  fact  that  their  name  was  given 
them,  as  the  ancients  believed  that  they  conveyed  air  to  the  various  parts 


100 


HANDBOOK    OF    PHYSIOLOGY, 


of  the  body.  As  regards  the  arterial  system  of  the  lungs  (pulmonary 
system)  it  begins  at  the  right  ventricle  in  the  pulmonary  artery,  and  is 
distributed  much  as  the  arteries  belonging  to  the  general  systemic  circu- 
lation 

Structure. — The  walls  of  the  arteries  are  composed  of  three  principal 
coats,  termed  (a)  the  external  or  tunica  adventitia,  (b)  the  middle  or 
tunica  media,  and  (c)  the  internal  or  tunica  intima. 

(a)  The  external  coat  or  tunica  adventitia  (Figs.  95  and  96  a),  the 
strongest  and  toughest  part  of  the  wall  of  the  artery,  is  formed  of  areo- 
lar tissue,  with  which  is  mingled  throughout  a  network  of  elastic  fibres. 
At  the  inner  part  of  this  outer  coat  the  elastic  network  forms  in  most 
arteries  so  distinct  a  layer  as  to  be  sometimes  called  the  external  elastic 
coat  (Fig.  99,  e  e). 


Fig.  97 


Fig. 


Fig.  97.— Portion  of  a  fenestrated  membrane  from  the  femoral  artery, 
tions.    (Henle.) 

Fig.  98.— Muscular  fibre-cells  from  human  arteries,  magnified  350  diameters. 
Nucleus,    b.  A  fibre-cell  treated  with  acetic  acid. 


X  200.    a,  b,  c,  Perfora- 
(Kolliker.)    a. 


(b)  The  middle  coat  (Fig.  95,  m)  is  composed  of  both  muscular  and 
elastic  fibres,  with  a  certain  proportion  of  areolar  tissue.  In  the  larger 
arteries  (Fig.  99)  its  thickness  is  comparatively  as  well  as  absolutely 
much  greater  than  in  the  small,  constituting,  as  it  does,  the  greater  part 
of  the  arterial  wall. 

The  muscular  fibres,  which  are  of  the  unstriped  variety  (Fig.  98). 
are  arranged  for  the  most  part  transversely  to  the  long  axis  of  the  artery 
(Fig.  95,  m);  while  the  elastic  element,  taking  also  a  transverse  direc- 
tion, is  disposed  in  the  form  of  closely  interwoven  and  branching  fibres, 
which  intersect  in  all  parts  the  layers  of  muscular  fibre.  In  arteries  of 
various  size  there  is  a  difference  in  the  proportion  of  the  muscular  and 
elastic  element,  elastic  tissue  preponderating  in  the  largest  arteries, 
while  this  condition  is  reversed  in  those  of  medium  and  small  size. 


THE   CIRCULATION    OF   THE    ISLOOD. 


1<>7 


(c)  The  internal  coat  is  formed  by  layers  of  elastic  tissue,  consisting 
in  part  of  coarse  longitudinal  branching  fibres,  and  in  part  of  a  very 
thin  and  brittle  membrane  which  possesses  little  elasticity,  and  is  thrown 


mmmm 
piliiir 


Fig.  99.— Transverse  section  of  aorta  through  internal  and  ahout  half  the  middle  coat.  a.  Lining 
endothelium  with  the  nuclei  of  the  cells  only  shown.  />.  Subepithelial  layer  of  connective  tissue,  c, 
d.  Elastic  tunica  intima  proper,  with  fibrils  ran  rung  circularly  or  longitudinally,  e,/.  .Middle  coat, 
consist  iug  of  elastic  fibres  arranged  longitudinally,  with  muscular  fibres,  cut  obliquely  or  longitu- 
dinally.   (Klein.) 

into  folds  or  wrinkles  when  the  artery  contracts.-    This  latter  mem- 
brane, the  striated  or  fenestrated  coat  of  Henle  (Fig.  97),  is  peculiar  in 


Fig.  100.— Transverse  section  of  small  artery  from  soft  palate,  e,  endothelial  lining,  the  nuclei 
of  the  cells  are  shown  :  /.  elastic  tissue  of  the'intima,  which  is  a  goo  I  deal  folded  :  <\  rn,  circular 
muscular  coat,  showing  nuclei  of  the  muscle  cells  ;  t.a,  tunica  advent  itia.    x  800.    (Schofleld.) 

its  tendency  to  curl  up,  when  peeled  off  from  the  artery,  and  in  the  per- 
forated and  streaked  appearance  which  it  presents  under  the  microscope. 
Its  inner  surface  is  lined  with  a  delicate  layer  of  elongated  endothelial 


10S 


HANDBOOK    OF    PHYSIOLOGY, 


cells  (Fig.  101,  a),  which  make  it  smooth  and  polished,  and  furnish  a 
nearly  impermeable  surface,  along  which  the  blood  may  flow  with  the 
smallest  possible  amount  of  resistance  from  friction. 


Fig.  101.— Two  blood-vessels  from  a  frog's  mesentery,  injected  with  nitrate  of  silver,  showingtne 
•outlines  of  the  endothelial  cells,  a.  Artery.  The  endothelial  cells  are  long  and  narrow;  the  trans- 
verse markings  indicate  the  muscular  coat.  t.a.  Tunica  adventitia.  v.  Vein,  showing  the  shorter 
and  wider  endothelial  cells  with  which  it  is  lined;  c,c.  two  capillaries  entering  the  vein.  (Scho- 
field.;) 


Fig.  102.— Blood-vessels  from  mesocolon  of  rabbit,  a.  Artery,  with  two  branches,  showing  tr. 
n.  nuclei  of  transverse  muscular  fibres;  l.n.  nuclei  of  endothelial  lining;  t.a.  tunica  adventitia.  v. 
Vein.  Here  the  transverse  nuclei  are  more  oval  than  those  of  the  artery.  The  vein  receives  a  small 
branch  at  the  lower  end  of  the  drawing;  it  is  distinguished  from  the  artery  among  other  things  by 
its  straighter  course  and  larger  calibre,  c  Capillary,  showing  nuclei  of  endothelial  cells.  X  300. 
fSchofield.) 


TIIE   CIRCULATION    OF   THE    BLOOD.  109 

Immediately  external  to  the  endothelial  lining  of  the  artery  is  fine 
connective  tissue,  sub-endothelial  layer,  with  branched  corpuscles.  Thus 
the  internal  coat  consists  of  three  parts  (a)  an  endothelial  lining,  (b)  the 
sub-endothelial  layer,  and  (c)  elastic  layers. 

Vasa  Vasorum. — The  walls  of  the  arteries,  with  the  possible  excep- 
tion of  the  endothelial  lining  and  the  layers  of  the  internal  coat  imme- 
diately outside  it,  are  not  nourished  by  the  blood  which  they  convey,  but 
are,  like  other  parts  of  the  body,  supplied  with  little  arteries,  ending  in 
capillaries  and  veins,  which,  branching  throughout  the  external  coat,. 


Fig.  103.— Ramification  of  nerves  and  termination  in  the  muscular  coat  of  a  small  artery  of  the 
frog  (Arnold  > . 

extend  for  some  distance  into  the  middle,  but  do  not  reach  the  internal 
coat.     These  nutrient  vessels  are  called  vasa  vasorum. 

Nerves. — Most  of  the  arteries  are  surrounded  by  a  plexus  of  sympa- 
thetic nerves,  which  twine  around  the  vessel  very  much  like  ivy  round 
a  tree:  and  gangli  are  found  at  frequent  intervals.  The  smallest  arte- 
ries and  capillaries  are  also  surrounded  by  a  very  delicate  network  of 
similar  nerve-tibres,  many  of  which  appear  to  end  in  the  nuclei  of  the 
transverse  muscular  fibres  (Fig.  103). 

III.  The  Capillaries. 

Distribution. — In  all  vascular  textures  except  some  parts  of  the  cor- 
pora cavernosa  of  the  penis,  and  of  the  uterine  placenta,  and  of  the 
spleen,  the  transmission  of  the  blood  from  the  miuute  branches  of  the 
arteries  to  the  minute  veins  is  effected  through  a  network  of  capillaries. 
They  may  be  seen  in  all  minutely  injected  preparations. 

The  point  at  which  the  arteries  terminate  and  the  minute  veins  com- 


110 


HANDBOOK    OF   PHYSIOLOGY, 


mence  cannot  be  exactly  defined,  for  the  transition  is  gradual;  but 
the  capillary  network  has,  nevertheless,  this  peculiarity,  that  the  small 
vessels  which  compose  it  maintain  the  same  diameter  throughout:  they 
do  not  diminish  in  diameter  in  one  direction,  like  arteries  and  veins; 
and  the  meshes  of  the  network  that  they  compose  are  more  uniform  in 
shape  and  size  than  those  formed  by  the  anastomoses  of  the  minute  ar- 
teries and  veins. 

Structure. — This  is  much  more  simple  than  that  of  the  arteries  or 
veins.     Their  walls  are  composed  of  a  single  layer  of  elongated  or  radi- 


Fig.  105. 


Fig.  104.— Blood-vessels  of  an  intestinal  villus,  representing  the  arrangement  of  capillaries  be- 
tween the  ultimate  venous  and  arterial  branches;  a,  a,  the  arteries;  b,  the  veiD. 

Fig.  105.— Capillary  blood-vessels  from  the  omentum  of  rabbit,  showing  the  nucleated  endothe- 
lial membrane  of  which  they  are  composed.     (Klein  and  Noble  Smith.) 

ate,  flattened  and  nucleated  cells,  so  joined  and  dovetailed  together  as  to 
form  a  continuous  transparent  membrane  (Fig.  105).  Outside  these 
cells,  in  the  larger  capillaries,  there  is  a  structureless,  or  very  finely 
fibrillated  membrane,  on  the  inner  surface  of  which  they  are  laid  down. 

In  some  cases  this  external  membrane  is  nucleated,  and  may  then  be 
regarded  as  a  miniature  representative  of  the  tunica  adventitia  of  arteries. 

Here  and  there,  at  the  junction  of  two  or  more  of  the  delicate  endo- 
thelial cells  which  compose  the  capillary  wall,  pseudo-stomata  may  be 
seen  (p.  22).  The  endothelial  cells  are  often  continuous  at  various 
points  with  processes  of  adjacent  connective-tissue  corpuscles. 

Capillaries  are  surrounded  by  a  delicate  nerve-plexus  resembling,  in 
miniature,  that  of  the  larger  blood-vessels. 

The  diameter  of  the  capillary  vessels  varies  somewhat  in  the  differ- 
ent textures  of  the  body,  the  most  common  size  being  about  yo^th  of 


THE    CIRCULATION    OF   THE    BLOOD. 


m 


an  inch.  Among  the  smallest  may  be  mentioned  those  of  the  brain, 
and  of  the  follicles  of  the  mucous  membrane  of  the  intestines;  among 
the  largest,  those  of  the  skin,  and  especially  those  of  the  medulla  of 
bones. 

The  size  of  capillaries  varies  necessarily  in  different  auimals  in  rela- 
tion to  the  size  of  their  blood-corpuscles:  thus,  in  the  Proteus,  the 
capillary  circulation  can  just  be  discerned  with  the  naked  eye. 

The  form  of  the  capillary  network  presents  considerable  variety  in  the 
different  textures  of  the  body:  the  varieties  consisting  principally  of 
modifications  of  two  chief  kinds  of  mesh,  the  rounded  and  the  elongated. 
That  kind  in  which  the  meshes  or  interspaces  have  a  roundish  form  is 
the  most  common,  and  prevails  in  those  parts  in  which  the  capillary  net- 
work is  most  dense,  such  as  the  lungs  (Fig,  10G),  most  glands,  and 
mucous  membranes,  and  the  cutis.     The  meshes  of  this  kind  of  network 


Fig.  106.  Fig.  107. 

Fig.  106.— Network  of  capillary  vessels  of  the  air-cells  of  the  horse's  lung  magnified,    a,  a, 
capillaries  proceeding  from  b,  h,  terminal  branches  of  the  pulmonary  artery.    iFrey.) 

Fig.  107.— Injected  capillary  vessels  of  muscle  seen  with  a  low  magnifying  power.    (Sharpey.) 

are  not  quite  circular,  but  more  or  less  angular,  sometimes  presenting  a 
nearly  regular  quadrangular  or  polygonal  form,  but  being  more  fre- 
quently irregular.  The  capillary  network  with  elongated  meshes  (Fig. 
107)  is  observed  in  parts  in  which  the  vessels  are  arranged  among  bundles 
of  fine  tubes  or  fibres,  as  in  muscles  and  nerves.  In  such  parts,  the 
meshes  usually  have  the  form  of  a  parallelogram,  the  short  sides  of 
which  may  be  from  three  to  eight  or  ten  times  less  than  the  long  ones; 
the  long  sides  always  corresponding  to  the  axis  of  the  fibre  or  tube,  by 
which  it  is  placed.  The  appearance  of  both  the  rounded  and  elongated 
meshes  is  much  varied  according  as  the  vessels  composing  them  have  a 
straight  or  tortuous  form.  Sometimes  the  capillaries  have  a  looped 
arrangement,  a  single  capillary  projecting  from  the  common   network 


112  HANDBOOK    OF    PHYSIOLOGY. 

into  some  prominent  organ,  and  returning  after  forming  one  or  more 
loops,  as  in  the  papillae  of  the  tongue  and  skin. 

The  number  of  the  capillaries  and  the  size  of  the  meshes  in  different 
parts  determine  in  general  the  degree  of  vascularity  of  those  parts. 
The  parts  in  which  the  network  of  capillaries  is  closest,  that  is,  in  which 
the  meshes  or  interspaces  are  the  smallest,  are  the  lungs  and  the  choroid 
membrane  of  the  eye.  In  the  iris  and  ciliary  body,  the  interspaces  are 
somewhat  wider,  yet  very  small.  In  the  human  liver  the  interspaces  are 
of  the  same  size,  or  even  smaller  than  the  capillary  vessels  themselves. 
In  the  human  lung  they  are  smaller  than  the  vessels;  in  the  human  kid- 
ney, and  in  the  kidney  of  a  dog,  the  diameter  of  the  injected  capillaries, 
compared  with  that  of  the  interspaces,  is  in  the  proportion  of  one  to 
four,  or  of  one  to  three.  The  brain  receives  a  very  large  quantity  of 
blood;  but  the  capillaries  in  which  the  blood  is  distributed  through  its 
substance  are  very  minute,  and  less  numerous  than  in  some  other  parts. 
Their  diameter,  according  to  E.  H.  Weber,  compared  with  the  long 
diameter  of  the  meshes,  being  in  the  proportion  of  one  to  eight  or  ten; 
compared  with  the  transverse  diameter,  in  the  proportion  of  one  to  four 
or  six.  In  the  mucous  membranes — for  example  in  the  conjunctiva  and 
in  the  cutis  vera,  the  capillary  vessels  are  much  larger  than  in  the  brain, 
and  the  interspaces  narrower — namely,  not  more  than  three  or  four  times 
wider  than  the  vessels.  In  the  periosteum  the  meshes  are  much  larger. 
In  the  external  coat  of  arteries,  the  width  of  the  meshes  is  ten  times  that 
of  the  vessels  (Henle). 

It  may  be  held  as  a  general  rule,  that  the  more  active  the  functions 
of  an  organ  are,  the  more  vascular  it  is.  Hence  the  narrowness  of  the 
interspaces  in  all  glandular  organs,  in  mucous  membranes,  and  in  grow- 
ing parts;  their  much  greater  width  in  bones,  ligaments,  and  other  very 
tough  and  comparatively  inactive  tissues;  and  the  usually  complete 
absence  of  vessels  in  cartilage,  and  such  parts  as  those  in  which,  prob- 
ably, very  little  vital  change  occurs  after  they  are  once  formed. 

IV.  The  Veins. 

Distribution. — The  venous  system  begins  in  small  vessels  which  are 
slightly  larger  than  the  capillaries  from  which  they  spring.  These  ves- 
sels are  gathered  up  into  larger  and  larger  trunks  until  they  terminate 
(as  regards  the  systemic  circulation)  in  the  two  vense  cavas  and  the  coro- 
nary veins,  which  enter  the  right  auricle,  and  (as  regards  the  pulmonary 
circulation)  in  four  pulmonary  veins,  which  enter  the  left  auricle.  The 
total  capacity  of  the  veins  diminishes  as  they  approach  the  heart  ;  but, 
as  a  rule,  their  capacity  exceeds  by  twice  or  three  times  that  of  their 
corresponding  arteries.  The  pulmonary  veins,  however,  are  an  excep- 
tion to  this  rule,  as  they  do  not  exceed  in  capacity  the  pulmonary  arte- 
ries.    The  veins  are  found  after  death  as  a  rule  to  be  more  or  less  col- 


THE    CIRCULATION    OF    THE    BLOOD. 


113 


lapsed,  and  often  to  contain  blood.  The  veins  are  usually  distributed 
in  a  superficial  and  a  deep  set  which  communicate  frequently  in  their 
course. 


Fig  108  -Transverse  section  through  a  small  artery  and  veiu  of  the  mucous  menibane  of  a 
child'se'piglottis:  the  contrast  between  the  thick-walled  artery  and  the  thin-balled  vein  is  well  shown 
A  Artery  the  letter  is  placed  in  the  lumeD  of  the  vessel,  e.  Endothelial  cells  with  nuclei  clearly  vis- 
ible- these  cells  appear  very  thick  from  the  contracted  state  of  the  vessel.  Outside  it  a  double  wavy 
line 'marks  the  elastic  tunica  intinia.  m.  Tunica  media  forming  the  chief  part  of  arterial  wall  and 
consisting  of  unstriped  muscular  fibres  circularly  arranged:  their  nuclei  are  well  seen.  a.  Part  of 
the  tunica  adventitia  showing  bundles  of  connective-tissue  fibre  in  section,  with  the  circular  nuclei 
of  the  connective-tissue  corpuscles.  This  coat  gradually  merges  into  the  surrounding  connective 
tissue  V.  In  the  lumen  of  the  vein.  The  other  letters  indicate  the  same  as  in  the  artery.  The 
muscular  coat  of  the  vein  (m)  is  seen  to  be  much  thinner  than  that  of  the  artery.  X  350.  (Klein 
and  Noble  Smith.) 


Fig.  109.— Diagram  showing  valves  of  veins,  a,  part  of  a  vein  laid  open  and  spread  out,  with 
two  pairs  of  valves,  b,  longitudinal  section  of  a  vein,  showing  the  apposition  of  the  edges  of 
the  valves  in  their  closed  state,  c,  portion  of  a  distended  vein,  exhibiting  a  swelling  in  the  situation 
of  a  pair  of  valves. 

Structure. — In  structure  the  coats  of  veins  bear  a  general  resemblance 
to  those  of  arteries  (Fig.  108).  Thus,  they  possess  an  outer,  middle,  and 
internal  coat.  The  outer  coat  is  constructed  of  areolar  tissue  like  that 
of  the  arteries,  but  is  thicker.  In  some  veins  it  contains  muscular  fibre- 
cells,  which  are  arranged  longitudinally. 
S 


114 


HANDBOOK    OF    PHYSIOLOGY. 


The  middle  coat  is  considerably  thinner  than  that  of  the  arteries  ; 
and,  although  it  contains  circular  unstriped  muscular  fibres  or  fibre-cells, 
these  are  mingled  with  a  larger  proportion  of  yellow  elastic  and  white 
fibrous  tissue.  In  the  large  veins,  near  the  heart,  namely  the  vence  cavce 
and  pulmonary  veins,  the  middle  coat  is  replaced,  for  some  distance  from 
the  heart,  by  circularly  arranged  striped  muscular  fibres,  continuous  with 
those  of  the  auricles. 

•  The  internal  coat  of  veins  is  less  brittle  than  the  corresponding  coat 
of  an  artery,  but  in  other  respects  resembles  it  closely. 

Valves. — The  chief  influence  which  the  veins  have  in  the  circulation, 
is  effected  with  the  help  of  the  valoes,  which  are  placed  in  all  veins  sub- 
ject to  local  pressure  from  the  muscles  between  or  near  which  they  run. 
The  general  construction  of  these  valves  is  similar  to  that  of  the  semi- 


Fig.  110.-A,  vein  with  valves  open,    b,  vein  with  valves  closed:  stream  of  blood  passing  off  by 
lateral  channel.    (Dalton.) 

lunar  valves  of  the  aorta  and  pulmonary  artery,  already  described ;  but 
their  free  margins  are  turned  in  the  opposite  direction,  i.e.,  towards  the 
heart,  so  as  to  stop  any  movement  of  blood  backward  in  the  veins. 
They  are  commonly  placed  in  pairs,  at  various  distances  in  different 
veins,  but  almost  uniformly  in  each  (Fig.  109).  In  the  smaller  veins, 
single  valves  are  often  met  with  ;  and  three  or  four  are  sometimes  placed 
together,  or  near  one  another,  in  the  largest  veins,  such  as  the  subclavian, 
and  at  their  junction  with  the  jugular  veins.  The  valves  are  semilunar; 
the  unattached  edge  being  in  some  examples  concave,  in  others  straight. 
They  are  composed  of  inextensile  fibrous  tissue,  and  are  covered  with 
endothelium  like  that  lining  the  veins.  During  the  period  of  their  in- 
action, when  the  venous  blood  is  flowing  in  its  proper  direction,  they  lie 
by  the  sides  of  the  veins  ;  but  when  in  action,  they  close  together  like 
the  valves  of  the  arteries,  and  offer  a  complete  barrier  to  any  backward 


THE   CIRCULATION    OK    THE   J5EOOD. 


115 


movement  of  the  blood  (Figs.  100  and  110).  Their  situation  in  the  su- 
perficial veins  of  the  fore-arm  is  readily  discovered  by  pressing  along  its 
surface,  in  a  direction  opposite  to  the  venous  current,  i.e.,  from  the  el- 
bow towards  the  wrist  ;  when  little  swell- 
ings (Fig.  109  c)  appear  in  the  position  of 
each  pair  of  valves.  These  swellings  at 
once  disappear  when  the  pressure  is  re- 
laxed. 

Valves  are  not  equally  numerous  in  all 
veins,  and  in  many  they  are  absent  alto- 
gether. They  are  most  numerous  in  the 
veins  of  the  extremities,  and  more  so  in 
those  of  the  leg  than  the  arm.  They  are 
commonly  absent  in  veins  of  less  than  a 
line  in  diameter,  and,  as  a  general  rule, 
there  are  few  or  none  in  those  which  are 
not  subject  to  muscular  pressure.  Among 
those  veins  which  have  no  valves  may  be 
mentioned  the  superior  and  inferior  vena 
cava,  the  trunk  and  branches  of  the 
portal  vein,  the  hepatic  and  renal  veins 
and  the  pulmonary  veins;  those  in  the 
interior  of  the  cranium  and  vertebral  col- 
umn, those  of  the  bones,  and  the  trunk 
and  branches  of  the  umbilical  vein  are 
also  destitute  of  valves. 

Lymphatics  of  Arteries  and  Veins. — 
Lymphatic  spaces  are  present  in  the 
coats  of  both  arteries  and  veins;  but  in  the  tunica  adventitia  or 
external  coat  of  large  vessels  they  form  a  distinct  plexus  of  more  or  less 
tubular  vessels.  In  smaller  vessels  they  appear  as  sinous  spaces  lined  by 
endothelium.  Sometimes,  as  in  the  arteries  of  the  omentum,  mesentery, 
and  membranes  of  the  brain,  in  the  pulmonary,  hepatic,  and  splenic 
arteries,  the  spaces  are  continuous  with  vessels  which  distinctly  ensheath 
them — perivascular  lymphatic  sheaths  (Fig.  111).  Lymph  channels  :ire 
said  to  be  present  also  in  the  tunica  media. 


Fig.  1 1 1 . —Surface  view  of  an  arte ry 
from  the  mesentery  of  a  frog,  eii- 
sheathed  in  a  perivascular  lymphatic 
vessel,  a.  The  artery,  with  its  circular 
muscular  coat  (media)  indicated  by 
broad  transverse  markings,  with  an 
indication  of  the  adventitia  outside. 
I.  Lymphatic  vessel  :  its  wall  is  a 
simple  endothelial  membrane.  (Klein 
and  Noble  Smith. ) 


The  Action  of  the  Heart. 


The  heart's  action  in  propelling  the  blood  consists  in  the  successive 
alternate  contraction  (systole)  and  relaxation  (diastole)  of  the  muscular 
walls  of  its  two  auricles  and  two  ventricles. 

1.  Action  of  the  Auricles. — The  description  of  the  action  of  the 
heart  may  be  commenced  at  that  period  in  each  action  which  immediately 


116  HANDBOOK    OF    PHYSIOLOGY. 

precedes  the  beat  of  the  heart  against  the  side  of  the  chest.  At  this 
period  the  whole  heart  is  in  a  passive  state,  the  walls  of  both  auricles  and 
ventricles  are  relaxed,  and  their  cavities  are  becoming  dilated.  The 
auricles  are  gradually  filling  with  blood  flowing  into,  them  from  the 
veins;  and  a  portion  of  this  blood  passes  at  once  through  them  into  the 
ventricles,  the  opening  between  the  cavity  of  each  auricle  and  that  of 
its  corresponding  ventricle  being,  during  all  the  pause,  free  and  patent. 
The  auricles,  however,  receiving  more  blood  than  at  once  passes  through 
them  to  the  ventricles,  become,  near  the  end  of  the  pause,  fully  distended ; 
and  at  the  end  of  the  pause,  they  contract  and  expel  their  contents  into 
the  ventricles. 

The  contraction  of  the  auricles  is  sudden  and  very  quick;  it  com- 
mences at  the  entrance  of  the  great  veins  into  them,  and  is  thence  pro- 
pagated towards  the  auriculo-ventricular  opening;  but  the  last  part 
which  contracts  is  the  auricular  appendix.  The  effect  of  this  contraction 
of  the  auricles  is  to  quicken  the  flow  of  blood  from  them  into  the  ven- 
tricles; the  force  of  their  contraction  not  being  sufficient  under  ordinary 
circumstances  to  cause  any  hack-flow  in  the  veins.  The  reflux  of  blood 
into  the  great  veins  is  moreover  resisted  not  only  by  the  mass  of  blood  in 
the  veins  and  the  force  with  which  it  streams  into  the  auricles,  but  also 
by  the  simultaneous  contraction  of  the  muscular  coats  with  which  the 
large  veins  are  provided  near  their  entrance  into  the  auricles.  Any  slight 
regurgitation  from  the  right  auricle  is  limited  also  by  the  valves  at  the 
junction  of  the  subclavian  and  internal  jugular  veins,  beyond  which  the 
blood  cannot  move  backwards;  and  the  coronary  vein  is  preserved  from 
it  by  a  valve  at  its  mouth. 

In  birds  and  reptiles  regurgitation  from  the  right  auricle  is  prevented 
by  valves  placed  at  the  entrance  of  the  great  veins. 

During  the  auricular  contraction  the  force  of  the  blood  propelled  into 
the  ventricle  is  transmitted  in  all  directions,  but  being  insufficient  to 
separate  the  semilunar  valves,'  it  is  expended  in  distending  the  ventricle, 
and,  by  a  reflux  of  the  current,  in  raising  and  gradually  closing  the  au- 
riculo-ventricular valves,  which,  when  the  ventricle  is  full,  form  a  com- 
plete septum  between  it  and  the  auricle. 

2.  Action  of  the  Ventricles.— The  blood  which  is  thus  driven,  by 
the  contraction  of  the  auricles,  into  the  corresponding  ventricles,  teing 
added  to  that  which  had  already  flowed  into  them  during  the  heart's 
pause,  is  sufficient  to  complete  their  diastole.  Thus  distended,  they 
immediately  contract:  so  immediately,  indeed,  that  their  systole  looks  as 
if  it  were  continuous  with  that  of  the  auricles.  The  ventricles  contract 
much  more  slowly  than  the  auricles,  and  in  their  contraction  probably 
always  thoroughly  empty  themselves,  differing  in  this  respect  from  the 
auricles,  in  which,  even  after  their  complete  contraction,  a  small  quan- 


THE    CIRCULATION    OF   THE    BLOOD.  117 

feity  of  blood  remains.  The  shape  of  both  ventricles  during  systole 
undergoes  an  alteration,  the  left  probably  not  altering  in  length  but  toa 
certain  degree  in  breadth,  the  diameters  in  the  plane  of  the  base  being 
diminished.  'The  right  ventricle  does  actually  shorten  to  a  small  extent. 
The  systole  has  the  effect  of  diminishing  the  diameter  of  the  base,  espe- 
cially in  the  plane  of  the  auriculo-ventricular  valves;  but  the  length  of 
the  heart  as  a  whole  is  not  altered.  (Ludwig.)  During  the  systole  of 
the  ventricles,  too,  the  aorta  and  pulmonary  artery,  being  filled  with 
blood  by  the  force  of  the  ventricular  action  against  considerable  resist- 
ance, elongate  as  well  as  expand,  and  the  whole  heart  moves  slightly  to- 
wards the  right  and  forwards,  twisting  on  its  long  axis,  and  exposing 
more  of  the  left  ventricle  anteriorly  than  is  usually  in  front.  When  the 
systole  ends  the  heart  resumes  its  former  position,  rotating  to  the  left 
again  as  the  aorta  and  pulmonary  artery  contract. 

Functions  of  the  Valves  of  the  Heart. — (1)  The  Auricula-  Ventric- 
ular.— The  distention  of  the  ventricles  with  blood  continues  throughout 
the  whole  period  of  their  diastole.  The  auriculo-ventricular  valves  are 
gradually  brought  into  place  by  some  of  the  blood  getting  behind  the 
cusps  and  floating  them  up;  and  by  the  time  that  the  diastole  is  complete, 
the  valves  are  no  doubt  in  apposition,  the  completion  of  this  being 
brought  about  by  the  reflux  current  caused  by  the  systole  of  the  auricles. 
This  elevation  of  the  auriculo-ventricular  valves  is  materially  aided  by 
the  action  of  the  elastic  tissue  which  has  been  shown  to  exist  so  largely 
in  their  structure,  especially  on  the  auricular  surface.  At  any  rate  at 
the  commencement  of  the  ventricular  systole  they  are  completely  closed. 
It  should  be  recollected  that  the  diminution  in  the  breadth  of  the  base 
of  the  heart  in  its  transverse  diameters  during  ventricular  systole  is  es- 
pecially marked  in  the  neighborhood  of  the  auriculo-ventricular  rings, 
and  this  aids  in  rendering  the  auriculo-ventricular  valves  competent  to 
close  the  openings,  by  greatly  diminishing  their  diameter.  The  margins 
of  the  cusps  of  the  valves  are  still  more  secured  in  apposition  with  an- 
other, by  the  simultaneous  contraction  of  the  musculi  papillares,  whose 
chorda}  tendineas  have  a  special  mode  of  attachment  for  this  object  (p. 
104).  The  cusps  of  the  auriculo-ventricular  valves  meet  not  by  their 
edges  only,  but  by  the  opposed  surfaces  of  their  thin  outer  borders. 

The  form  and  position  of  the  fleshy  columns  of  the  internal  walls 
of  the  ventricle  no  doubt  help  to  produce  the  obliteration  of  the  ventric- 
ular cavity  during  contraction  ;  and  the  completeness  of  the  closure 
may  often  be  observed  on  making  a  transverse  section  of  a  heart  shortly 
after  death,  in  any  case  in  which  rigor  mortis  is  very  marked  (Fig.  91). 
In  such  a  case  only  a  central  fissure  may  be  discernible  to  the  eye  in  the 
place  of  the  cavity  of  each  ventricle. 

If  there  were  only  circular  fibres  forming  the  ventricular  wall,  it  is 
evident  that  on  systole  the  ventricle  would  elongate  ;   if  there  were   only 


IIS  HANDBOOK    OF    PHYSIOLOGY. 

longitudinal  fibres  the  ventricle  would  shorten  on  systole  ;  but  there  are 
both.  The  tendency  to  alter  in  length  is  thus  counter-balanced,  and  the 
whole  force  of  the  contraction  is  expended  in  diminishing  the  cavity  of 
the  ventricle  ;  or,  in  other  words,  in  expelling  its  contents. 

On  the  conclusion  of  the  systole  the  ventricular  walls  tend  to  expand 
by  virtue  of  their  elasticity,  and  a  negative  pressure  is  set  up,  which 
tends  to  suck  in  the  blood.  This  negative  or  suctional  pressure  on  the 
left  side  of  the  heart  is  of  the  highest  importance  in  helping  the  pul- 
monary circulation.  It  has  been  found  to  be  equal  to  23  mm.  of  mer- 
cury, and  is  quite  independent  of  the  aspiration  or  suction  power  of  the 
thorax,  which  will  be  described  in  the  chapter  on  Respiration. 

Function  of  the  Musculi  Papillares. — The  special  function  of  the 
musculi  papillares  is  to  prevent  the  auriculo-ventricular  valves  from  be- 
ing everted  into  the  auricle.  For  the  chordae  tendineae  might  allow  the 
valves  to  be  pressed  back  into  the  auricle,  were  it  not  that  when  the  wall 
of  the  ventricle  is  brought  by  its  contraction  nearer  the  auriculo-ventric- 
ular orifice,  the  musculi  papillares  more  than  compensate  for  this  by 
their  own  contraction — holding  the  cords  tight,  and,  by  pulling  down 
the  valves,  adding  slightly  to  the  force  with  which  the  blood  is  expelled. 

What  has  been  said  applies  equally  to  the  auriculo-ventricular  valves 
on  both  sides  of  the  heart,  and  of  both  alike  the  closure  is  generally 
complete  every  time  the  ventricles  contract.  But  in  some  circumstances 
the  closure  of  the  tricuspid  valve  is  not  complete,  and  a  certain  quantity 
of  blood  is  forced  back  into  the  auricle.  This  has  been  called  the  safe- 
ty-valve action  of  this  valve.  The  circumstances  in  which  it  usually 
happens  are  those  in  which  the  vessels  of  the  lung  are  already  full 
enough  when  the  right  ventricle  contracts,  as  e.  g.,  in  certain  pulmonary 
diseases,  in  very  active  exertions,  and  in  great  efforts.  In  these  cases, 
the  tricuspid  valve  does  not  completely  close,  and  the  regurgitation  of 
the  blood  may  be  indicated  by  a  pulsation  in  the  jugular  veins  synchro- 
nous with  that  in  the  carotid  arteries. 

(2)  Of  the  Semilunar  Valves. — The  arterial  or  semilunar  valves  are 
forced  apart  by  the  out-streaming  blood,  with  which  the  contracting 
ventricle  dilates  the  large  arteries.  The  dilatation  of  the  arteries  is,  in  a 
peculiar  manner,  adapted  to  bring  the  valves  into  action.  The  lower- 
borders  of  the  semilunar  valves  are  attached  to  the  inner  surface  of  the 
tendinous  ring,  which  is,  as  it  were,  inlaid  at  the  orifice  of  the  artery, 
between  the  muscular  fibres  of  the  ventricle  and  the  elastic  fibres  of  the 
walls  of  the  artery.  The  tissue  of  this  ring  is  tough,  and  does  not  admit 
of  extension  under  such  pressure  as  it  is  commonly  exposed  to ;  the 
valves  are  equally  incxtensile,  being,  as  already  mentioned,  formed 
mainly  of  tough,  close-textured,  fibrous  tissue,  with  strong  interwoven 
cords.  Hence,  when  the  ventricle  propels  blood  through  the  orifice  and 
into  the  canal  of  the  artery,  the  lateral  pressure   which   it  exercises  is 


THE    CIRCULATION    OF    THE    BLOOD. 


1U» 


sufficient  to  dilate  the  walls  of  the  artery,  hut  not  enough  to  stretch  in 
an  equal  degree,  if  at  all,  the  unyielding  valves  and  the  ring  to  which 
their  lower  borders  are  attached.  The  effect,  therefore,  of  each  such 
propulsion  of  blood  from  the  ventricle  is,  that  the  Avail  of  the  first  por. 


Fig.  112.  -Sections  of  aorta,  to  show  the  action  of  the  semilunar  valves,  a  is  intended  to  show  the 
valves,  represented  by  the  dotted  lines,  lying  near  the  arterial  walls,  represented  by  the  continuous 
outer  line,  b  (after  Hunter)  shows  the  arterial  wall  distended  into  three  pouches  (a),  and  drawn 
away  from  the  valves,  which  are  straightened  into  the  form  of  an  equilateral  triangle,  as  represent- 
ed by  the  dotted  lines. 

tion  of  the  artery  is  dilated  into  three  pouches  behind  the  valves,  while 
the  free  margins  of  the  valves  are  drawn  inward  towards  its  centre  (Fig. 
112  b).     Their  positions  may  be  explained  by  the  diagrams,   in  which 


Fig.  113.— View  of  the  base  of  the  ventricular  part  of  the  heart,  showing  the  relative  position  of  the 
arterial  and  aurieulo- ventricular  orifices.  -  0 .  The  muscular  fibres  of  the  ventricles  are  exposed  by 
the  removal  of  the  pericardium,  fat,  blood-vessels,  etc.;  the  pulmonary  artery  and  aorta  have  been 
removedby  a  section  made  immediately  beyond  the  attachment  of  the  semilunar  v'ves,  and  the 
auricles  have  been  removed  immediately  above  the  auriculo-ventricular  orifices.  The  semilunar 
and  auriculo-ventricular  valves  are  in  the  nearly  closed  condition.  1,  1,  the  base  of  Hi<'  right  ven- 
tricle; 1',  the  conus  arteriosus:  2,  -i,  the  base  of  the  left  ventricle;  8,  8,  the  divided  wall  of  the  right 
auricle;  4,  thatof  the  left;  5,  5  5",  the  tricuspid  valve;  6,  6',  the  mitral  valve,  in  the  angles  \»- 
tween  these  segments  are  seen  the  smaller  fringes  frequently  observed;  T,  the  anterior  part  of  the 
pulmonary  artery;  8,  placed  upon  the  posterior  part  of  the  root  of  the  aorta;  9,  the  right,  9',  the  left 
coronary  artery.     (Allen  Thomson  i 

the  continuous  lines  represent  a  transverse  section  of  the  arterial  walls, 

the  dotted  ones  the  edges  of  the  valves,  firstly,  when  the  valves  are  near- 
est to  the  walls  (a),  as  in  the  dead  heart,  and.  secondly,  when,  the  walls 
being  dilated,  the  valves  are  drawn  away  from  them  (b). 


J2i)  HANDBOOK    OF    PHYSIOLOGY. 

This  position  of  the  valves  and  arterial  walls  is  retained  so  long  as  the 
ventricle  continues  in  contraction  :  but,  as  soon  as  it  relaxes,  and  the 
dilated  arterial  walls  can  recoil  by  their  elasticity,  the  blood  is  forced 
backwards  towards  the  ventricles  as  onwards  in  the  course  of  the  circu- 
lation. Part  of  the  blood  thus  forced  back  lies  in  the  pouches  (sinuses 
of  Valsalva)  (a,  Fig.  112,  b)  between  the  valves  and  the  arterial  walls  ; 
and  the  valves  are  by  it  pressed  together  till  their  thin  lunated  margins 
meet  in  three  lines  radiating  from  the  centre  to  the  circumference  of  the 
artery  (7  and  8,  Fig.  113). 

The  contact  of  the  valves  in  this  position,  and  the  complete  closure 
of  the  arterial  orifice,  are  secured  by  the  peculiar  construction  of  their 
borders  before  mentioned.     Among  the  cords  which  are  interwoven  in 

the  substance  of  the  valve,  are  two  of  greater 
strength  and  prominence  than  the  rest ;  of 
which  one  extends  along  the  free  border  of 
each  valve,  and  the  other  forms  a  double 
curve  or  festoon  just  below  the  free  border. 
Each  of  these  cords  is  attached  by  its  outer 
extremities  to  the  outer  end  of  the  free  margin 
of  its  valve,  and  in  the  middle  to  the  corpus 
Arantii;  they  thus  inclose  a  lunated  space 
from  a  line  to  a  line  and  a  half  in  width,  in 
which  space  the  substance  of  the  valve  is 
much  thinner  and  more  pliant  than  elsewhere. 
fig.   114. -Vertical  section      When  the  valves  are  pressed  down,  all  these 

through  the  aorta  at  its  junction  .     ,  „  . 

with  the  left  ventricle,   a,  Seq-      parts   or  spaces  oi  their  surfaces  come  into 

tion  of  aorta,  bb,  Section  of  two        1  .    .  .    -        ._ 

valves,  c,  section  of  wail  of  ven-       contact,  and  the  closure  oi  the  arterial  ormce 

tricle.     d,    Internal  surface   of  .   .  ,      ,,, 

ventricle.  is  thus  secured  by  the  apposition  not  or  the  mere 

edges  of  the  valves,  but  of  all  those  thin  lunated  parts  of  each  which  lie 
between  the  free  edges  and  the  cords  next  below  them.  These  parts  are 
firmly  pressed  together,  and  the  greater  the  pressure  that  falls  on  them 
the  closer  and  more  secure  is  their  apposition.  The  corpora  Arantii 
meet  at  the  centre  of  the  arterial  orifice  when  the  valves  are  down,  and 
they  probably  assist  in  the  closure  ;  but  they  are  not  essential  to  it,  for, 
not  uufrequently,  they  are  wanting  in  the  valves  of  the  pulmonary 
artery,  which  are  then  extended  in  larger,  thin,  flapping  margins.  In 
valves  of  this  form,  also,  the  inlaid  cords  are  less  distinct  than  in  those 
with  corpora  Arantii  ;  yet  the  closure  by  contact  of  their  surfaces  is  not 
less  secure. 

It  has  been  clearly  shown  that  this  pressure  of  the  blood  is  not  en- 
tirely sustained  by  the  valves  alone,  but  in  part  by  the  muscular  substance 
of  the  ventricle  (Savory).  By  making  vertical  sections  (Fig.  114) 
through  various  parts  of  the  tendinous  rings  it  is  possible  to  show  clearly 
that  the  aorta  and  pulmonary  artery,  expanding  towards  their  termina- 


THK    CIRCULATION    OF    THK    BLOOD.  121 

tion,  are  situated  upon  the  outer  edge  of  the  thick  ripper  border  of  the 
ventricles,  and  that  consequently  the  portion  of  each  .semilunar  valve 
adjacent  to  the  vessel  passes  over  and  rests  upon  the  muscular  substance 
— being  thus  supported,  as  it  were,  on  a  kind  of  muscular  floor  formed 
by  the  upper  border  of  the  ventricle.  The  result *of  this  arrangement  is 
that  the  reflux  of  the  blood  is  most  efficiently  sustained  by  the  ventricu- 
lar wall. 

As  soon  as  fhe  auricles  have  completed  their  contraction  they  begin 
again  to  dilate,  and  to  be  refilled  with  blood,  which  flows  into  them  in  a 
steady  stream  through  the  the  great  venous  trunks.  Indeed,  a  chief  func- 
tion of  the  auricles  is  to  form  a  receptacle  for  the  on-streaming  blood 
during  the  ventricular  contraction.  They  are  thus  filling  during  all  the 
time  in  which  the  ventricles  are  contracting  ;  and  the  contraction  of  the 
ventricles  being  ended,  these  also  again  dilate,  and  receive  again  the 
blood  that  flows  into  them  from  the  auricles.  By  the  time  that  the  ven- 
tricles are  thus  from  one-third  to  two-thirds  full,  the  auricles  are  dis- 
tended :  these,  then  suddenly  contracting,  fill  up  the  ventricles,  as  already 
described  (p.  116). 

Cardiac  Cycle. — If  we  supjwse  a  cardiac  cycle  divided  into  five 
parts,  one  of  these  will  be  occupied  by  the  contraction  of  the  auricles, 
two  by  that  of  the  ventricles,  and  two  by  repose  of  both  auricles  and 
ventricles. 

Contraction  of  Auricles,    .  '   .     .     1  +    Repose  of  Auricles,       .     4  =  5 

"  Ventricles,           .     %  +         "      '•  Ventricles,    .     3  =  5 
Repose  (no  contraction  of  either 

auricles  or  ventricles),        .     .     2  +   Contraction  (of  either  au- 

—  ricles  or  ventricles), .     3=5 
5 

If  the  speed  of  the  heart  be  quickened,  the  time  occupied  by  each 
eardiac  revolution  is  of  course  diminished,  but  the  diminution  affects 
only  the  diastole  and  pause.  The  systole  of  the  ventricles  occupies  very 
much  the  same  time,  about  T*r  sec,  whatever  the  pulse-rate. 

The  periods  in  which  the  several  valves  of  the  heart  are  in  action 
may  be  connected  with  the  foregoing  table;  for  the  auriculo-ventricular 
valves  are  closed,  and  the  arterial  valves  are  open  during  the  whole  rime 
of  the  ventricular  contraction,  while,  during  the  dilation  and  distention 
of  the  ventricles,  the  latter  valves  are  shut,  the  former  open.  Thus 
whenever  the  auriculo-ventricular  valves  are  open,  the  arterial  valves  are 
closed  and  vice  versa. 

The  Sounds  of  the  Heart. 

When  the  ear  is  placed  over  the  region  of  the  heart,  two  sounds  may 
be  heard  at  every  beat  of  the  heart,  which  follow  in  quick  succession. 
and  are  succeeded  by  a  pause  or  period  of  silence.     The  first  sound  is 


122  HANDBOOK    OF   PHYSIOLOGY. 

dull  and  prolonged;  its  commencement  coincides  with  the  movement  or 
impulse  of  the  heart  against  the  chest  wall,  and  just  precedes  the  pulse 
at  the  wrist.  The  second  is  a  shorter  and  sharper  sound,  with  a  some- 
what flapping  character;  and  follows  close  after  the  arterial  pulse.  The 
period  of  time  occupied  respectively  by  the  two  sounds  taken  together, 
and  by  the  pause,  are  almost  exactly  equal.  The  relative  length  of  time 
occupied  by  each  sound,  as  compared  with  the  other,  is  a  little  uncer- 
tain. The  difference  may  be  best  appreciated  by  considering  the  differ- 
ent forces  concerned  in  the  production  of  the  two  sounds.  In  one  case 
there  is  a  strong,  comparatively  slow,  contraction  of  a  large  mass  of 
muscular  fibres,  urging  forward  a  certain  quantity  of  fluid  against  con- 
siderable resistance;  while  in  the  other  it  is  a  strong  but  shorter  and 
sharper  recoil  of  the  elastic  coat  of  the  large  arteries — shorter  because 
there  is  no  resistance  to  the  flapping  back  of  the  semilunar  valves,  as 
there  was  to  their  opening.  The  sounds  may  be  expressed  by  saying  the 
words  lubb — dup  (C.  J.  B.  Williams). 

The  events  which  correspond,  in  point  of  time,  with  the  first  sound 
are  (1)  the  contraction  of  the  ventricles,  (2)  the  first  part  of  the  dilata- 
tion of  the  auricles,  (3)  the  tension  of  the  auriculo-ventricular  valves, 
(4)  the  opening  of  the  semilunar  valves,  and  (5)  the  propulsion  of  blood 
into  the  arteries.  The  sound  is  succeeded,  in  about  one-thirtieth  of  a 
second,  by  the  pulsation  of  the  facial  arteries,  and  in  about  one-sixth  of 
a  second,  by  the  pulsation  of  the  arteries  at  the  wrist.  The  second 
sound,  in  point  of  time,  immediately  follows  the  cessation  of  the 
ventricular  contraction,  and  corresponds  with  (a)  the  tension  of  the  semi- 
lunar valves,  (b)  the  continued  dilatation  of  the  auricles,  (c)  the  com- 
mencing dilatation  of  the  ventricles,  and  (d)  the  opening  of  the  auriculo- 
ventricular  valves.  The  pause  immediately  follows  the  second  sound, 
and  corresponds  in  its  first  part  with  the  completed  distention  of  the 
auricles,  and  in  its  second  with  their  contraction,  and  the  completed 
distention  of  the  ventricles;  the  auriculo-ventricular  valves  being,  all 
the  time  of  the  pause,  open,  and  the  arterial  valves  closed. 

Causes. — The  exact  causes  of  the  first  sound  of  the  heart  are  not 
exactly  known.  Two  factors  probably  enter  into  it,  viz.,  the  vibration 
of  the  auriculo-ventricular  valves  and  chordas  tend ineas,  due  to  their 
stretching,  and  also,  but  to  a  less  extent,  of  the  ventricular  walls,  and 
coats  of  the  aorta  and  pulmonary  artery,  all  of  which  parts  are  suddenly 
put  into  a  state  of  tension  at  the  moment  of  ventricular  contraction; 
and  secondly  the  muscular  sound  produced  by  contraction  of  the  mass 
of  muscular  fibres  which  form  the  ventricle.  The  first  factor  is  probably 
the  more  important. 

The  cause  of  the  second  sound  is  more  simple  than  that  of  the  first. 
It  is  probably  due  entirely  to  the  vibration  consequent  on  the  sudden 
closure  of  the  semilunar  valves  when  they  are  pressed  down  across  the 


THE    CIRCULATION'    OF   THE    BLOOD.  1'2'4 

orifices  of  the  aorta  and  pulmonary  artery.  The  influence  of  the  valves 
in  producing  the  sound  is  illustrated  by  the  experiment  performed  on 
large  animals,  such  as  calves,  in  which  the  results  could  be  fully  appre- 
ciated. In  thesa  experiments  two  delicate  curved  needles  were  inserted, 
one  into  the  aorta,  and  another  into  the  pulmonary  artery,  below  the  line 
of  attachment  of  the  semilunar  valves,  and,  after  being  carried  upwards 
about  half  an  inch,  were  brought  out  again  through  the  coats  of  the 
respective  vessels,  so  that  in  each  vessel  one  valve  was  included  between 
the  arterial  walls  and  the  wire.  Upon  applying  the  stethoscope  to  the 
vessels,  after  such  an  operation,  the  second  sound  had  ceased  to  be  audi- 
ble. Disease  of  these  valves,  when  so  extensive  as  to  interfere  with  their 
efficient  action,  also  often  demonstrates  the  same  fact  by  modifying  or 
destroying  the  distinctness  of  the  second  sound. 

One  reason  for  the  second  sound  being  a  clearer  and  sharper  one  than 
the  first  may  be,  that  the  semilunar  valves  are  not  covered  in  by  the  thick 
layer  of  fibres  composing  the  walls  of  the  heart  to  such  an  extent  as  are 
the  auriculo -ventricular.  It  might  be  expected  therefore  that  their 
vibration  would  be  more  easily  heard  through  a  stethoscope  applied  to 
the  walls  of  the  chest. 

The  contraction  of  the  auricles  which  takes  place  in  the  end  of  the 
pause  is  inaudible  outside  the  chest,  but  may  be  heard,  when  the  heart 
is  exposed  and  the  stethoscope  placed  on  it,  as  a  slight  sound  preceding 
and  continued  into  the  louder  sound  of  the  ventricular  contraction. 

The  Impulse  of  the  Heart. 

At  the  commencement  of  each  ventricular  contraction,  the  heart  may 
be  felt  to  beat  with  a  slight  shock  or  impulse  against  the  walls  of  the 
chest.  The  force  of  the  impulse,  and  the  extent  to  which  it  may  be 
perceived  beyond  this  point,  vary  considerably  in  different  individual-, 
and  in  the  same  individual  under  different  circumstances.  It  is  felt 
more  distinctly,  and  over  a  larger  extent  of  surface,  in  emaciated  than  in 
fat  and  robust  persons,  and  more  during  a  forced  expiration  than  in  a 
deep  inspiration;  for,  in  the  one  case,  the  intervention  of  a  thick  layer 
of  fat  or  muscle  between  the  heart  and  the  surface  of  the  chest,  and  in 
the  other  the  inflation  of  the  portion  of  lung  which  overlaps  the  heart. 
prevents  the  impulse  from  being  fully  transmitted  to  the  surface.  An 
excited  action  of  the  heart,  and  especially  a  hypertrophied  condition  of 
the  ventricles,  will  increase  the  impulse;  while  a  depressed  condition,  or 
an  atrophied  state  of  the  ventricular  walls,  will  diminish  it. 

Cause  of  the  Impulse. — During  the  period  which  precedes  the  ven- 
tricular systole,  the  apex  of  the  heart  is  situated  upon  the  diaphragm 
and  against  the  chest-wall  in  the  fifth  intercostal  space.  When  the  ven- 
tricles contract,  their  walls  become  hard  and  tense,  since  to  expel  their 


12  4: 


HANDBOOK    OF    PHYSIOLOGY. 


contents  into  the  arteries  is  a  distinctly  laborious  action,  as  it  is  resisted 
by  the  elasticity  of  the  vessels.  It  is  to  this  sudden  hardening  that  the 
impulse  of  the  heart  against  the  chest-wall  is  due,  and  the  shock  of  the 
sudden  tension  may  be  felt  not  only  externally,  but  also  internally,  if  the 
abdomen  of  an  animal  be  opened  and  the  finger  be  placed  upon  the 
under  surface  of  the  diaphragm,  at  a  point  corresponding  to  the  under 
surface  of  the  ventricle.  The  shock  is  felt,  and  possibly  seen  more  dis- 
tinctly because  of  the  partial  rotation  of  the  heart,  already  spoken  of, 
along  its  long  axis  towards  the  right.  The  movement  produced  by  the 
ventricular  contraction  against  the  chest-wall  may  be  registered  by  means 
of  an  instrument  called  the  cardiograph,  and  it  will  be  found  to  corre- 
spond almost  exactly  with  a  tracing  obtained  by  the  same  instrument 
applied  over  the  contracting  ventricle  itself. 

The  Cardiograph  (Fig.  115)  consists  of  a  cup-shaped  metal  box 
over  the  open  front  of  which  is  stretched  an  elastic  india-rubber  mem- 
brane, upon  which  is  fixed  a  small  knob  of  hard  wood  or  ivory.  This 
knob,  however,  may  be  attached  instead,  as  in  the  figure,  to  the  side  of 

the  box  by  means  of  a  spring,  and  may  be 
made  to  act  upon  a  metal  disc  attached  to  the 
elastic  membrane. 

The  knob  (a)  is  for  application  to  the 
chest- wall  over  the  place  of  the  greatest  im- 
pulse of  the  heart.  The  box  or  tympanum 
communicates  by  means  of  an  air-tight  elastic 
tube  (f)  with  the  interior  of  a  second  tym- 
panum (Fig.  116,  b),  in  connection  with 
which  is  a  long  and  light  lever  (a).  The 
shock  of  the  heart's  impulse  being  communi- 
cated to  the  ivory  knob,  and  through  it  to 
the  first  tympanum,  the  effect  is,  of  course, 
at  once  transmitted  by  the  column  of  air  in 
the  elastic  tube  to  the  interior  of  the  second 
tympanum,  also  closed,  and  through  the 
elastic  and  movable  lid  of  the  latter  to  the 
lever,  which  is  placed  in  connection  with  a  registering  apparatus.  This 
generally  consists  of  a  cylinder  or  drum  covered  with  smoked  paper, 
revolving  according  to  a  definite  velocity  by  clock-work.     The  point  of 


Fig.  115.— Cardiograph, 
derson's.) 


(San- 


Fig.  116  —  Marey's  Tambour  (7>),  to  which  the  movement  of  the  column  of  air  in  the  first  tympa- 
num is  conducted  by  the  tube,  /,  and  from  which  it  is  communicated  by  the  lever  a,  to  a  revolving 
cylinder,"  so  that  the  tracing  of  the  movement  of  the  impulse  beat  is  obtained. 


THE    CIKOl'LATION"    OF  THE    BLOOD. 


125 


tlie  lever  writes  upon  the  paper,  and   a  tracing  of  the  heart's  impulse  or 
cardiogram^  is  thus  obtained. 

By  placing  three  small  india-rubber  air-bags  or  cardiac  sounds  in  the 
interior  respectively  of  the  right  auricle,  the  right  ventricle,  and  in  an 
intercostal  space  in  front  of  the  heart  of  living  animals  (horse),  and 
placing  these  bags,  by  means  of  long  narrow  tubes,  in  communication 
with  three  levers,  arranged  one  over  the  other  in  connection  with  a  re- 
gistering apparatus  (Fig.  117),  MM.  Ohauveau  and  Marey  have  been  able 


Fig.  117.— Apparatus  of  MM.  Ohauveau  and  Marey  for  estimating  the  variations  of  endocardial 
pressure,  and  production  of  impulse  of  the  heart. 

to  record  and  measure  with  much  accuracy  the  variations  of  the  endocar- 
dial pressure  and  the  comparative  duration  of  the  contractions  of  the 
auricles  and  ventricles.  By  means  of  the  same  apparatus,  the  synchron- 
ism of  the  impulse  with  the  con- 
traction of  the  ventricles,  is  also  well 
shown;  and  the  causes  of  the  several 
vibrations  of  which  it  is  really  com- 
posed, have  been  demonstrated. 

In  the  tracing  (Fig.  118).  the  inter- 
vals between  the  vertical  lines  repre- 
sent periods  of  a  tenth  of  a  second. 
The  parts  on  which  any  given  vertical 
line  falls  represent  simultaneous  events. 
It  will  be  seen  that  the  contraction  of 
the  auricle,  indicated  by  the  marked 
curve  at  a  in  first  tracing,  causes  a 
slight  increase  of  pressure  in  the  ven- 
tricle, which  is  shown  at  A.'  in  the  sec- 
ond tracing,  and  produces  also  a  slight 
impulse,  which  is  indicated  by  a"  in 
the  third  tracing.  The  closure  of  the 
semilunar  valves  causes  a  momentarily 
increased  pressure  in  the  ventricle  at  u'  affects  the  pressure  in  the  auri- 
cle d,  and  is  also  shown  in  the  tracing  of  the  impulse  also,  n". 

The  large  curve  of  the  ventricular  and  the  impulse  tracings,  between 
a'  and  n',  and  a"  and  i>".  are  caused  by  the  ventricular  contraction, 
while  the  smaller  undulations,  between  Band  C,  b'  and  C',  B''  andc".  are 


l'u;  IIS.— Tracings  of  (1  >,  Intra-auri- 
cular,  and  (2),  Intra-ventricular  pressures, 
and  (8),  of  the  impulse  ot  the  heart,  to  he 
read  from  left  to  right,  obtained  by  Ohau- 
veau and  Ma  ivy's  apparatus. 


126  HANDBOOK    OF   PHYSIOLOGY. 

caused  by  the  vibrations  consequent  on  the  tightening  and  closure  of  the 
auriculo-ventricular  valves. 

The  method  thus  described  may,  as  a  rule,  demonstrate  quite  cor- 
rectly the  variations  of  endocardial  pressure,  and  these  variations  only, 
hut  there  is  a  danger  lest  the  muscular  walls  should  grip  the  air-bags, 
•even  after  the  complete  expulsion  of  the  fluid  contents  of  the  chamber, 
and  if  so  the  lever  would  remain  at  its  highest  point  for  too  long  a  time. 
The  highest  curve  under  such  circumstances  would  represent  on  the 
tracing  not  only,  as  it  ought  to  do,  the  endocardiac  pressure,  but  also  in 
addition  the  muscular  pressure  exerted  upon  the  cardiac  sound  itself. 
(M.  Foster.) 

Frequency  and  Force  of  the  Heart's  Action. 

The  heart  of  a  healthy  adult  man  contracts  from  seventy  to  seventy- 
five  times  in  a  minute  ;  but  many  circumstances  cause  this  rate,  which 
of  course  corresponds  with  that  of  the  arterial  pulse,  to  vary  even  in 
health.  The  chief  are  age,  temperament,  sex,  food  and  drink,  exercise, 
time  of  day,  posture,  atmospheric  pressure,  temperature. 

(I.)  Age. — The  frequency  of  the  heart's  action  gradually  diminishes 
from  the  commencement  to  near  the  end  of  life,  but  is  said  to  rise  again 
somewhat  in  extreme  old  age,  thus  : — 

Before  birth  the  average  number  of  pulsations  per  minute  is  150 

Just  after  birth, from  140  to  130 

During  the  first  year, 

During  the  second  year,         .... 
During  the  third  year,       .         .         .         . 
About  the  seventh  year,         .... 
About  the  fourteenth  year,  the  average  number 

of  pulses  in  a  minute  is  from 
In  adult  age,  ...... 

In  old  age,      ' 

In  decrepitude, 

(2.)  Temperament  and  Sex. — In  persons  of  sanguine  temperament, 
the  heart  acts  somewhat  more  frequently  than  in  those  of  the  phleg- 
matic ;  and  in  a  female  sex  more  frequently  than  in  the  male. 

(3  and  4.)  Food  and  Drink,  Exercise. — After  a  meal  the  heart's  ac- 
tion is  accelerated,  and  still  more  so,  during  bodily  exertion  or  mental 
excitement ;  it  is  slower  during  sleep. 

(5.)  Diurnal  Variation. — In  the  state  of  health,  the  pulse  is  most 
frequent  in  the  morning,  and  becomes  gradually  slower  as  the  day  ad- 
vances :  and  that  this  diminution  of  frequency  is  both  more  regular  and 
more  rapid  in  the  evening  than  in  the  morning. 

(6.)  Posture. — The  pulse,  as  a  general  rule,  especially  in  the  adult 
male,  is  more  frequent  in  the  standing  than  in  the  sitting  posture,  and 
in  the  latter  than  in  the  recumbent  position  ;  the  difference  being  great- 
est between  the  standing  and  the  sitting  postures.  The  effect  of  change 
of  posture  is  greater  as  the  frequency  of  the  pulse  is  greater,  and,  ac- 
cordingly, is  more  marked  in  the  morning  than  in  the  evening.  By 
supporting  the  body  in  different  positions,  without  the  aid  of  muscular 


130  to  115 

115  to  100 

100  to 

90 

90  to 

85 

85  to 

80 

80  to 

70 

70  to 

60 

75  to 

65 

THE    CIRCULATION    OF    TIJE    BLOOD.  1  '1  ~ 

effort  of  the  individual,  it  has  been  proved  that  the  increased  frequency 
of  the  pulse  in  the  sitting  and  standing  positions  is  dependent  upon  the 
muscular  exertion  engaged  in  maintaining  them  ;  the  usual  effect  of 
these  postures  on  the  pulse  being  almost  entirely  prevented  when  the 
usually  attendant  muscular  exertion  was  rendered  unnecessary.     (Guy.) 

(7.)  Atmospheric  Pressure. — The  frequency  of  the  pulse  increases  in 
a  corresponding  ratio  with  the  elevation  above  the  sea. 

(8. )  Temperature. — The  rapidity  and  force  of  the  heart's  contractions 
are  largely  influenced  by  variations  of  temperature.  The  frog's  heart, 
when  excised,  ceases  to  beat  if  the  temperature  be  reduced  to  32° F.  (0° 
C).  When  heat  is  gradually  applied  to  it,  both  the  speed  and  force  of 
the  contractions  increase  till  they  reach  a  maximum.  If  the  tempera- 
ture is  still  further  raised,  the  beats  become  irregular  and  feeble,  and  the 
heart  at  length  stands  still  in  a  condition  of  ''  heat  rigor." 

Similar  effects  are  produced  in  warm-blooded  animals.  In  the  rabbit, 
the  number  of  heart-beats  is  more  than  doubled  when  the  temperature 
of  the  air  was  maintained  at  105°  F.  (40°.5  C).  At  113°-L14°  F.  (45° 
C),  the  rabbit's  heart  ceases  to  beat. 

Relative  Frequency  of  the  Heart's  Contractions  to  the  number  of  Res- 
pirations.— In  health  there  is  observed  a  nearly  uniform  relation  between 
the  frequency  of  the  beats  of  the  heart  and  of  the  respirations  ;  the  pro- 
portion being,  on  an  average,  oue  respiration  to  three  or  four  beats. 
The  same  relation  is  generally  maintained  in  the  cases  in  which  the  ac- 
tion of  the  heart  is  naturally  accelerated,  as  after  food  or  exercise;  but 
in  disease  this  relation  usually  ceases.  In  many  affections  accompanied 
with  increased  frequency  of  the  heart's  contraction,  the  respiration  is, 
indeed,  also  accelerated,  yet  the  degree  of  its  acceleration  may  bear  no 
definite  proportion  to  the  increased  number  of  the  heart's  actions  :  and 
in  many  other  cases,  the  heart's  contraction  becomes  more  frequent  with- 
out any  accompanying  increase  in  the  number  of  respirations  ;  or,  the 
respiration  alone  may  be  accelerated,  the  number  of  pulsations  remain- 
ing stationary,  or  even  falling  below  the  ordinary  standard. 

The  Force  of  the  Ventricular  Action. — The  force  of  the  left  ven- 
tricular systole  is  more  than  double  that  exerted  by  the  contraction  of 
the  right  ventricle  :  this  difference  results  from  the  walls  of  the  left 
ventricle  being  about  twice  or  three  times  as  thick  as  those  of  the  right. 
And  the  difference  is  adapted  to  the  greater  degree  of  resistance  which 
the  left  ventricle  has  to  overcome,  compared  with  that  to  be  overcome 
by  the  right  :  the  former  having  to  propel  blood  through  every  part  of 
the  body,  the  latter  only  through  the  lungs.  The  actual  amount  of  the 
intra-ventricular  pressures  during  systole  in  the  dog  has  been  found  to 
be  2.4  inches  (GO  mm.)  of  mercury  in  the  right  ventricle,  and  6  inches 
(150  mm.)  in  the  left. 

During  diastole  there  is  in  the  right  ventricle  a  negative  or  suction 
pressure  of  about  |  of  an  inch  (—17  to  —16  mm.),  and  in  the  left  ven- 
tricle from  2  inches   to  $  of  an  inch  (  —  52  to  —20   mm.).      Part  of  this 


128  HANDBOOK    OF    PHYSIOLOGY. 

fall  in  pressure,  and  possibly  the  greater  part,  is  to  be  referred  to  the' 
influence  of  respiration  ;  but  without  this  the  negative  pressure  of  the 
left  ventricle  caused  by  its  active  dilatation  is  about  equal  to  4,  of  an 
inch  (23  mm.)  of  mercury. 

The  right  ventricle  is  undoubtedly  aided  by  this  suction  power  of  the 
left,  so  that  the  whole  of  the  work  of  conducting  the  pulmonary  circu- 
lation does  not  fall  upon  the  right  side  of  the  heart,  but  is  assisted  by 
the  left  side. 

The  Force  of  the  Auricular  Contractions. — The  maximum 
pressure  within  the  right  auricle  is  about  4  of  an  inch  (20  mm.)  of  mer- 
cury, and  is  probably  somewhat  less  in  the  left.  It  has  been  found  that 
during  diastole  the  pressure  within  both  auricles  sinks  considerably  be- 
low that  of  the  atmosphere  ;  and  as  some  fall  in  pressure  takes  place, 
even  when  the  thorax  of  the  animal  operated  upon  has  been  opened,  a 
certain  proportion  of  the  fall  must  be  due  to  active  auricular  dilatation 
independent  of  respiration.  In  the  right  auricle,  this  negative  pressure 
is  about  —10  mm. 

Work  Done  by  the  Heart. — In  estimating  the  work  done  by  any. 
machine  it  is  usual  to  express  it  in  terms  of  the  "  unit  work."  In  Eng- 
land, the  unit  of  work  is  the  ic  foot-pound,"  and  is  defined  to  be  the 
energy  expended  in  raising  a  unit  of  weight  (1  lb.)  through  a  unit  of 
height  (1  ft.)  :  in  France,  the  "  kilogram-metre." 

The  work  done  by  the  heart  at  each  contraction  can  be  readily  found 
by  multiplying  the  weight  of  the  blood  expelled  by  the  ventricles  by  the 
height  to  which  the  blood  rises  in  a  tube  tied  into  an  artery.  This 
height  was  found  to  be  about  9  ft.  in  the  horse,  and  this  estimate  is 
nearly  correct  for  a  large  artery  in  man.  Taking  the  weight  of  blood 
expelled  from  the  left  ventricle  at  each  systole  at  6  oz.,  i.  e.,  f  lb.,  we 
have  9  X  |=3.375  foot  pounds  as  the  work  done  by  the  left  ventricle  at 
each  systole  ;  and  adding  to  this  the  work  done  by  the  right  ventricle 
(about  one-third  that  of  the  left)  we  have  3. 375  x  1.125  =  1.5  foot-pounds 
as  the  work  done  by  the  heart  at  each  contraction.  Other  estimates  give 
\  kilogram-metre,  or  about  3\  foot-pounds.  Haughton  estimates  the 
total  work  of  the  heart  in  24  hours  as  about  124  foot-tons. 

Influence  of  the  Nervous  System  on  the  Action  of  the  Heart. 

The  hearts  of  warm-blooded  animals  cease  to  beat  very  soon  after 
removal  from  the  body,  and  are,  therefore,  unfavorable  for  the  study  of 
the  nervous  mechanism  which  regulates  their  action.  The  hearts  of 
cold-blooded  animals,  therefore,  e.  g.,  the  frog,  tortoise,  and  snake, 
which  will  continue  to  beat  under  favorable  conditions  for  many  hours 
after  removal  from  the  body,  are  generally  employed,  as  more  conveni- 
ent for  the  purpose.     Of  these  animals,  the  frog  is  the  one  most  fre- 


THE   CIRCULATION    OF   THE    BLOOD. 


129 


qnently  used,  and,  indeed,  until  recently,  it  was  from  the  study  of  the 
frog's  heart  that  the  chief  part  of  our  information  on  the  subject  was 
obtained.  If  removed  from  the  body  entire,  the  frog's  heart  will  con- 
tinue to  beat  for  many  hours  and  even  days,  and  the  beat  has  no  appa- 
rent difference  from  the  beat  of  the  heart  before  removal  from  the  body; 
it  will  take  place  without  the  presence  of  blood  or  other  fluid  within  its 
chambers.  If  the  beats  have  become  infrecpient,  an  additional  one  may 
be  induced  by  mechanically  stimulating  the  heart  by  means  of  a  blunt 
needle  ;  but  the  time  before  the  stimulus  applied  produces  its  results 
(the  latent  period)  is  very  prolonged,  and  as  in  this  way  the  cardiac  beat 
is  like  the  contraction  of  unstriped  muscle,  it  has  been  likened  to  a  peri- 
staltic contraction. 

There  is  much  uncertainty  about  the  nervous  mechanism  of  the  beat 


A.& 


Fig.  119a.  Fig.  119b. 

Fig.  119a.— The  Heart  of  a  Frog  fRanaesculentai  from  the  front.  V,  ventricle;  Ad,  right  auricle; 
As,  left  auricle;  B,  bulbus  arteriosus  dividing  into  right  and  left  aortse.     (Ecker.) 

Fig.  119b.  -  The  Heart  of  a  Frog  (Rana  esculenta)  from  the  back.  s.v.t  sinus  venosus  opened; 
C.8.S.,  left  vena  cava  superior;  c.s.d.,  right  vena  cava  superior;  c.i.,  vena  cava  inferior;  I7.jp.,  vena 
pulmonales;  A.d..  right  auricle;  A.s.,  left  auricle;  A.p.,  opening  of  communication  between  the 
right  auricle  and  the  sinus  venosus.      <  1)4—  3.     (Ecker.; 


of  the  frog's  heart,  but  what  has  just  been  said  shows,  at  any  rate,  two 
things  :  firstly,  that  as  the  heart  will  beat  when  removed  from  the  body 
in  a  way  differing  not  all  from  the  normal,  it  must  contain  within  itself 
the  mechanism  of  rhythmical  contraction  ;  and,  secondly,  that  as  it  can 
beat  without  the  presence  of  fluid  with  its  chambers,  the  movement  can- 
not depend  solely  on  reflex  excitation  by  the  entrance  of  blood. 

The  nervous  apparatus  existing  in  the  heart  itself  has  been  found  to 
consist  of  collections  of  microscopic  ganglia,  and  of  nerve-fibres  proceed- 
ing from  them.     These  ganglia   are   demonstrable  as  being  collected 

chiefly  into  three  groups:  one  is  in  the  wall  of  the  sinus  venosus  at  the 
9 


130 


HANDBOOK    OF    PHYSIOLOGY 


junction  of  the  sinus  with  the  auricles  (Remak's);  a  second,  near  the 
junction  between  the  auricles  and  ventricle  (Bidder's);  and  the  third  in 
the  septum  between  the  auricles. 

It  is  generally  believed  that  the  rhythmical  contractions  of  the  frog's 

heart  are,  under  ordinary  circum- 
stances, closely  associated  with  the 
ganglia.  Thus,  (1)  if  the  heart  be 
removed  entire  from  the  body,  the 
sequence  of  the  contraction  of  its  sev- 
eral beats  will  take  place  with  rhyth- 
mical regularity,  viz.,  of  the  sinus 
venosus,  the  auricles,  the  ventricle, 
and  bulbus  arteriosus,  in  order.  (2)  If 
the  heart  be  removed  at  the  junction 
of  the  sinus  and  auricle,  the  former, 
remaining  in  situ,  will  continue  to 
\'it|^|^^^^iiiii*^^^ihhl'          beat,  but  the  removed  portion  will  for 

a  short  variable  time  stop  beating,  and 
when  it  resumes  its  beats,  it  will  be 
with  a  different  rhythm  to  that  of  the 
sinus;  and,  further,  (3)  if  the  ventricle 
only  be  removed,  it  will  take  a  still  long- 
er time  before  recommencing  its  pul- 
sation after  its  removal  than  the  larger  "portion  consisting  of  the  auricles 
and  ventricle  does  in  experiment  (2),  and  its  rhythm  is  different  from 
that  of  the  unremoved  portion,  and  not  so  regular.  It  will  not  continue 
to  pulsate  so  long;  but  during  the  period  of  stoppage  a  contraction  will 
occur  if  it  be  mechanically  or  otherwise  stimulated.  (4)  If  the  lower 
two-thirds  or  apex  of  the  ventricle  be  removed,  the  remainder  of  the 
heart  will  go  on  beating  regularly  in  the  body,  but  the  part  removed  will 
remain  motionless  and  will  not  beat  spontaneously,  although  it  will  re- 
spond to  stimuli  by  a  single  beat  for  each  stimulus.  (5)  If  the  heart  be 
divided  lengthwise,  its  parts  will  continue  to  pulsate  rhythmically,  and 
the  auricles  may  be  cut  up  into  pieces,  and  the  pieces  will  continue  their 
movements  of  rhythmical  contraction. 

It  will  be  thus  seen  that  the  rhythmical  movements  appear  to  be  more 
marked  in  the  parts  supplied  by  the  ganglia,  and  that  the  apical  portion 
of  the  ventricle,  in  which  the  ganglia  are  not  found,  does  not,  under 
ordinary  circumstances,  possess  the  power  of  automatic  movement. 

It  has,  however,  been  shown  by  Gaskell  that  the  extreme  apex  of  the 
ventricle  of  the  heart  of  the  tortoise,  which  contains  no  ganglia,  may 
under  appropriate  stimuli  be  made  to  contract  rhythmically.  This 
proves  that  the  muscular  tissue  of  the  heart  is  capable  of  rhythmical 
contraction,  but  it  does  not  prove  that  in  the  living  animal  the  muscular 


Fig.  120.— Course  of  the  nerves  in  the 
auricular  partition  wall  of  the  heart  of  a 
frog,  d,  dorsal  branch;  v,  ventral  branch. 
(Ecker.) 


THE   CIRCULATIOX   OK   THE    HI.UOl". 


131 


Thythm  occurs  without  nervous  stimulation,  nor  indeed   is  this  at  all 
likely. 

Inhibition  of  the  Heart's  Action. — Although,  under  ordinary  con- 
ditions, the  apparatus  of  ganglia  and  nerve-fibres  in  the  substance  of  the 
heart  forms  the  medium  through  which  its  action  is  excited  and  rhythmi- 
cally maintained,  yet  they,  and  through  them,  the  heart's  contractions, 
are  regulated  by  nerves  which  pass  to  them  from  the  higher  nerve-cen- 
tres. These  nerves  are  branches  from  the  pnenmogastric  or  vagus  and 
the  sympathetic. 

The  influence  of  the  vagi  nerves  over  the  heart  beat  may  be  shown 
by  stimulating  one  (especially  the  right),  or  both  of  the  nerves,  when  a 
record  is  being  taken  of  the  beats  of  the  frog's  heart.  If  a  single  induc- 
tion shock  be  sent  into  the  nerve,  the  heart,  as  a  rule  after  a  short  inter- 
val, ceases  beating,  but  after  the  suppression  of  several  beats  resumes  its 
action.  As  already  mentioned, 
the  effect  of  the  stimulus  is  not 
immediately  seen,  and  one 
beat  may  occur  before  the 
heart  stops  after  the  applica- 
tion of  the  electric  current. 
The  stoppage  of  the  heart  may 
occur  apparently  in  one  of  two 
ways,  either  by  diminishing 
the  strength  of  the  systole  or  by 
increasing  the  length  of  the 
diastole  (Figs.  121,  122) 


■ 

nrnjuri1 

B 

H 

§1 

1 

Fig.  121.— Tracing  showing  the  actions  of  the  va- 
gus on  the  heart.  Aur.,  auricular;  Vent.,  ventricu- 
lar tracing.  The  part  between  perpendicular  lines 
indicates  period  of  vagus  stimulation.  C.8  indicates 
that  the  secondary  coil  was  8  cm.  from  the  primary. 
The  part  of  tracing  to  the  left  shows  the  regular  con- 
tractions of  moderate  height  before  stimulation.  Dur- 
ing stimulation  and  for  some  time  after  the  beats  of 
auricle  and  ventricle  are  arrested.  After  they  com- 
mence agaiD  they  are  single  at  first,  but  soon  acquire 
a  much  greater  amplitude  than  before  the  application 
of  the  stimulus.      (From  Brunton,  after  Gaskell .) 


The  stoppage  of  the  heart 
may  be  brought  about  by  the 
application  of  the  electrodes  to 
any  part  of  the  vagus,  but 
most    effectually    if    they  are 

applied  near  the  position  of  Eemak's  ganglia.  It  is  supposed  that  the 
fibres  of  the  vagi,  therefore,  terminate  there  in  the  ganglia  in  the  heart - 
Avails,  and  that  the  inhibition  of  the  heart's  beats  by  means  of  the  vagus 
is  not  a  direct  action,  but  that  it  is  brought  about  indirectly  by  stimu- 
lating these  centres  in  the  heart  itself.  If  this  idea  be  correct,  it  may 
bo  supposed  that  the  inhibitory  centres  are  paralyzed  by  injection  of 
-atropine,  as  after  this  has  been  done  no  amount  of  stimulation  of  the 
vagus,  or  of  the  heart  itself,  will  produce  any  effect  upon  the  cardiac 
beats.  Also  that  urari  in  large  doses  paralyzes  the  vagus  fibres,  but  as 
the  inhibitory  action  can  be  produced  by  direct  stimulation  of  the  heart, 
it  is  inferred  that  this  drug  does  not  paralyze  the  ganglia  themselves. 
Muscarin  and  pilocarpine  appear  to  produce  effects  similar  to  those  ob- 
tained by  stimulating  the  vagus  fibres.  They  stimulate  the  inhibitory 
ganglia. 

The  remarkable  effects  of  ligaturing  the  heart  at  various  parts  (Stan- 


132 


HANDBOOK   OF    PHYSIOLOGY. 


Fig.  122.— Tracing  showing  diminished  amplitude 
and  slowing  of  the  pulsations  of  the  auricle  and 
ventricle  without  complete  stoppage  during  irritation 
of  the  vagus.     CFrom  Brunton,  after  GaskellJ 


nius'  experiments)   however,   complicate  if  they  do  not  contradict  the 
above  explanation. 

If   a  ligature  be  tightly   tied  round  the   heart   over  the  situation 

of  the  ganglia  between  the 
sinus  and  the  auricles,  the 
heart  below  the  ligature  stops 
beating.  The  ligature  might 
be  supposed  to  stimulate  the 
inhibitory  ganglia,  but  for  the 
remarkable  fact  that  the  ex- 
hibition of  atropin  does  not 
interfere  with  the  success  of 
the  experiment. 

Section  of  the  heart  at  the 
same  situation  we  have  seen 
has  (experiment  'Z,  p.  130)  a 
similar  effect  to  ligature. 
Again,  if  the  ventricle  be 
separated  from  the  auricles  by  ligature  or  by  section,  it  will  recommence 
its  pulsation  and  continue  to  beat  rhythmically,  but  the  auricles  will  con- 
tinue at  a  standstill.  It  has  been  suggested  as  an  alternative  explanation 
of  these  further  experiments  that  the  sinus  contains  the  chief  motor 
ganglia  of  the  heart,  and  that  from  it  as  a  rule  proceed  the  impulses 
which  cause  the  sequence  of  contraction  of  the  other  parts  ;  that 
the  auricles  contain  inhibitory  ganglia  which  are  not  sufficiently  power- 
ful to  prevent  the  motor  impulses  from  the  sinus  ganglia,  but  that  when 
their  influence  is  removed  by  section,  by  ligature,  or  by  excessive  stimu- 
lation that  the  inhibitory  ganglia  are  able  to  prevent  the  rhythmical  con- 
traction of  the  auricles  and  ventricle,  but  that  the  ventricle  contains  in- 
dependent motor  ganglia,  since  when  it  is  removed  from  the  influence 
of  the  inhibitory  ganglia  of  the  auricles,  it  recommences  rhythmical  pul- 
sation. 

Even  if  this  theory  cannot  be  absolutely  maintained,  yet  it  is  evident 
that  the  power  of  spontaneous  contraction  is  strongest  in  the  sinus,  less 
strong  in  the  auricles,  and  less  so  still  in  the  ventricle,  and  that,  there- 
fore, the  sinus  ganglia  are  important  in  exciting  the  rhythmical  contrac- 
tion of  the  whole  heart. 


So  far,  the  effect  of  the  terminal  apparatus  of  the  vagi  only  has  been 
considered;  there  is,  however,  no  doubt  that  the  vagi  nerves  are  simply 
the  media  of  an  inhibitory  or  restraining  influence  over  the  action  of  the 
heart,  which  is  conveyed  through  them  from  a  centre  in  the  medulla  ob- 
longata which  is  always  in  operation,  and,  because  of  its  restraining  the 
heart's  action,  is  called  the  cardio-inliibitory  centre.  For,  on  dividing 
these  nerves,  the  pulsations  of  the  heart  are  increased  in  frequency,  an 
effect  opposite  to  that  produced  by  stimulation  of  their  divided  (peri- 
pheral) ends.  The  restraining  influence  of  the  centre  in  the  medulla 
may  be  reflexly  increased,  so  as  to  produce  slowing  or  stoppage  of  the 
heart,  through  impulses  from  it  passing  down  the  vagi.  As  an  example 
of  the  latter,  the  well-known  effect  on  the  heart  of  a  violent  blow  on  the 


THE   CIRCULATION    OF   THE  BLOOD.  133 

epigastrium  may  be  referred  to.  The  stoppage  of  the  heart's  action  in 
this  case,  is  due  to  the  conveyance  of  the  stimulus  by  fibres  of  the  sym- 
pathetic (afferent)  to  the  medulla  oblongata,  and  its  subsequent  reflection 
through  the  vagi  (afferent)  to  the  inhibitory  ganglia  of  the  heart.  It  is 
also  believed  that  the  power  of  the  medullary  inhibitory  centre  may  in  a 
similar  manner  be  reflexly  lessened  so  as  to  produce  accelerated  action  of 
the  heart. 

Acceleration  of  the  Heart's  Action. —  The  heart  receives  an  ac- 
celerating influence  from  the  medulla  oblongata  through  certain  fibres  of 
the  sympathetic.  These  accelerating  nerve-fibres,  issuing  from  the  spinal 
cord  in  the  lower  cervical  and  upper  dorsal  regions,  reach  the  inferior 
cervical  ganglion  of  the  sympathetic,  and  pass  thence  to  the  cardiac 
plexus,  and  so  to  the  heart.  Their  function  is  shown  in  the  quickened 
pulsation  which  follows  stimulation  of  the  spinal  cord,  when  the  latter 
has  been  cut  off  from  all  connection  with  the  heart,  excepting  by  these 
accelerating  filaments.  Unlike  the  inhibitory  fibres  of  the  pneumogas- 
tric,  the  accelerating  fibres  are  not  continuously  in  action. 

The  accelerator  nerves  must  not,  however,  be  considered  as  direct  an- 
tagonists of  the  vagus  ;  for  if  at  the  moment  of  their  maximum  stimula- 
tion, the  vagus  be  stimulated  with  minimum  currents,  inhibition  is 
produced  with  the  same  readiness  as  if  these  were  not  acting.  Nor  is 
there  any  evidence  that  these  fibres  are  constantly  in  action  like  those  of 
the  vagus. 

The  connection  of  the  heart  with  other  organs  by  means  of  the  ner- 
vous system,  and  the  influence  to  which  it  is  subject  through  them,  are 
shown  in  a  striking  manner  by  the  phenomena  of  disease.  The  influence 
of  mental  shock  in  arresting  or  modifying  the  action  of  the  heart,  the 
slow  pulsation  which  accompanies  compression  of  the  brain,  the  irregu- 
larities and  palpitations  caused  by  dyspepsia  or  hysteria,  are  good  evi- 
dence of  the  connection  of  the  heart  with  other  organs  through  the  ner- 
vous system. 

Other  Influences  affecting  the  Action  of  the  Heart. 

The  healthy  action  of  the  heart  no  doubt  very  materially  depends  (1) 
upon  a  due  supply  of  healthy  blood  to  its  muscular  tissue.  It  is  not  un- 
likely that  the  apparently  contradictory  effect  of  poisons  may  be  ex- 
plained by  supposing  that  the  influence  of  some  of  them  is  either 
partially  or  entirely  directed  to  the  muscular  tissue  itself  and  not  to  the 
nervous  apparatus  alone. 

As  will  be  explained  presently,  the  heart  exercises  a  considerable 
influence  upon  the  condition  of  the  pressure  of  blood  within  the  arteries 
but  in  its  turn  (2)  the  blood  pressure  within  the  arteries  reacts  upon  the 
heart,  and  has  a  distinct  effect  upon  its  contractions,  increasing  by  its 


134  HANDBOOK    OF    PHYSIOLOGY. 

increase,  and  vice  versa,  the  force  of  the  cardiac  beat,  although  the  fre- 
quency is  diminished  as  the  blood-pressure  rises.  (3)  The  quantity  {and 
quality  f)  of  the  blood  contained  in  its  chambers,  too,  has  an  influence 
upon  its  systole,  and  within  normal  limits  the  larger  the  quantity  the 
stronger  the  contraction.  Eapidity  of  systole  does  not  of  necessity  indi- 
cate strength,  as  two  weak  contractions  often  do  no  more  work  than  a, 
strong  and  prolonged  one.  (4)  In  order  that  the  heart  may  do  its  maxi- 
mum work,  it  must  be  alloived  free  space  to  act;  for  if  obstructed  in  its 
action  by  mechanical  outside  pressure,  as  by  an  excess  of  fluid  within 
the  pericardium,  such  as  is  produced  by  inflammation,  or  by  an  over- 
loaded stomach,  or  the  like,  the  pulsations  become  irregular  and  feeble. 

Functions  of  the  Arteries. 

The  External  Coat. — The  external  coat  forms  a  strong  and  tough 
investment,  which,  though  capable  of  extension,  appears  principally  de- 
signed to  strengthen  the  arteries  and  to  guard  against  their  excessive 
distention  by  the  force  of  the  heart's  action.  It  is  this  coat  which  alone 
prevents  the  complete  severance  of  an  artery  when  a  ligature  is  tightly 
applied  ;  the  internal  and  middle  coats  being  divided.  In  it,  too,  the 
little  vasa  vasorum  (p.  109)  find  a  suitable  tissue  in  which  to  subdivide 
for  the  supply  of  the  arterial  coats. 

The  Elastic  Tissue. — The  purpose  of  the  elastic  tissue,  which 
enters  so  largely  into  the  formation  of  all  the  coats  of  the  arteries,  is, 
(a)  to  guard  the  arteries  from  the  suddenly  exerted  pressure  to  which 
they  are  subjected  at  each  contraction  of  the  ventricles.  In  every  such 
contraction,  the  contents  of  the  ventricles  are  forced  into  the  arteries 
more  quickly  than  they  can  be  discharged  into  and  through  the  capilla- 
ries. The  blood  therefore,  being,  for  an  instant,  resisted  in  its  onward 
course,  a  part  of  the  force  with  which  it  was  impelled  is  directed  against 
the  sides  of  the  arteries  ;  under  this  force  their  elastic  walls  dilate, 
stretching  enough  to  receive  the  blood,  and  as  they  stretch,  becoming 
more  tense  and  more  resisting.  Thus,  by  yielding,  they  break  the  shock  of 
the  force  impelling  the  blood.  On  the  subsidence  of  the  pressure,  when 
the  ventricles  cease  contracting,  the  arteries  are  able,  by  the  same  elas- 
ticity, to  resume  their  former  calibre,  (b.)  It  equalizes  the  current  of 
the  blood  by  maintaining  pressure  on  it  in  the  arteries  during  the 
periods  at  which  the  ventricles  are  at  rest  or  dilating.  If  the  arteries 
had  been  rigid  tubes,  the  blood,  instead  of  flowing,  as  it  does,  in  a  con- 
stant stream,  would  have  been  propelled  through  the  arterial  system  in 
a  series  of  jerks  corresponding  to  the  ventricular  contractions,  with  in- 
tervals of  almost  complete  rest  during  the  inaction  of  the  ventricles. 
But  in  the  actual  condition  of  the  arteries,  the  force  of  the  successive 
contractions  of  the  ventricles  is  expended  partly  in  the  direct  propulsion 


THE    CIECULATION    OF    THE    BLOOD.  135 

of  the  blood,  and  partly  in  the  dilatation  of  the  elastic  arteries  ;  and  in 
the  intervals  between  the  contractions  of  the  ventricles,  the  force  of  the 
recoil  is  employed  in  continuing  the  same  direct  propulsion.  Of  course 
the  pressure  they  exercise  is  equally  diffused  in  every  direction,  and  the 
blood  tends  to  move  backwards  as  well  as  onwards,  but  all  movement 
backwards  is  prevented  by  the  closure  of  the  aortic  semi-lunar  valves 
(p.  104),  which  takes  place  at  the  very  commencement  of  the  recoil  of 
the  arterial  walls. 

By  this  exercise  of  the  elasticity  of  the  arteries,  all  the  force  of  the 
ventricles  is  expended  upon  the  circulation  ;  for  that  part  of  their  force 
which  is  used  in  dilating  the  arteries,  is  restored  in  full  when  they  recoil. 
There  is  thus  no  loss  of  force  ;  but  neither  is  there  any  gain,  for  the 
elastic  walls  of  the  artery  cannot  originate  any  force  for  the  propulsion 
of  the  blood — they  only  restore  that  which  they  received  from  the  ven- 
tricles. The  force  with  which  the  arteries  are  dilated  every  time  the 
ventricles  contract,  might  be  said  to  be  received  by  them  in  store,  to  be 
all  given  out  again  in  the  next  succeeding  period  of  dilatation  of  the 
ventricles.  It  is  by  this  equalizing  influence  of  the  successive  branches 
of  every  artery  that  at  length  the  intermittent  accelerations  produced 
in  the  arterial  current  by  the  action  of  the  heart,  cease  to  be  observable, 
and  the  jetting  stream  is  converted  into  the  continuous  and  equable 
movement  of  the  blood  which  we  see  in  the  capillaries  and  veins.  In  the 
production  of  a  continuous  stream  of  blood  in  the  smaller  arteries  aud 
capillaries,  the  resistance  which  is  offered  to  the  blood-stream  in  these 
vessels,  is  a  necessary  agent.  Were  there  no  greater  obstacle  to  the  es- 
cape of  blood  from  the  larger  arteries  than  exists  to  its  entrance  into 
them  from  the  heart,  the  stream  would  be  intermittent,  notwithstand- 
ing the  elasticity  of  walls  of  the  arteries. 

(c.)  By  means  of  the  elastic  and  muscular  tissue  in  their  walls  the 
arteries  are  enabled  to  dilate  and  contract  readily  in  correspondence 
with  any  temporary  increase  or  diminution  of  the  total  quantity  of  blood, 
in  the  body  ;  and  within  a  certain  range  of  diminution  of  the  quantity, 
still  to  exercise  due  pressure  on  their  contents;  (d. )  The  elastic  tissue 
assists  in  restoring  the  normal  state  after  diminution  of  its  calibre, 
whether  this  has  been  caused  by  a  contraction  of  the  muscular  coat,  or 
the  temporary  application  of  a  compressing  force  from  without.  This 
action  is  well  shown  in  arteries  which,  having  contracted  by  means  of 
their  muscular  element,  after  death,  regain  their  average  patency  on  the 
cessation  of  post-mortem  rigidity,  (e.)  By  means  of  their  elastic  coat 
the  arteries  are  enabled  to  adapt  themselves  to  the  different  movements 
of  the  several  parts  of  the  body. 

The  natural  state  of  all  arteries,  in  regard  at  least  to  their  length,  is 
one  of  tension — they  are  always  more  or  less  stretched,  and  ever  ready 
to  recoil  by  virtue  of  their  elasticity,  whenever  the  opposing  force  is  re- 


136  HANDBOOK    OF    PHYSIOLOGY. 

moved.  The  extent  to  which  the  divided  extremities  of  arteries  retract 
is  a  measure  of  this  tension,  not  of  their  elasticity.     (Savory.) 

The  Muscular  Coat. — The  most  important  office  of  the  muscular 
coat  is,  (1)  that  of  regulating  the  quantity  of  blood  to  be  received  by 
each  part  or  organ,  and  of  adjusting  it  to  the  requirements  of  each,  ac- 
cording to  various  circumstances,  but,  chiefly,  according  to  the  activity 
with  which  the  functions  of  each  are  at  different  times  performed.  The 
amount  of  work  done  by  each  organ  of  the  body  varies  at  different  times, 
and  the  variations  often  quickly  succeed  each  other,  so  that,  as  in  the 
brain,  for  example,  during  sleep  and  waking,  within  the  same  hour  a 
part  may  be  now  very  active  and  then  inactive.  In  all  its  active  exer- 
cise of  function,  such  a  part  requires  a  larger  supply  of  blood  than  is 
sufficient  for  it  during  the  times  when  it  is  comparatively  inactive.  It 
is  evident  that  the  heart  cannot  regulate  the  supply  to  each  part  at  dif- 
ferent periods  ;  neither  could  this  be  regulated  by  any  general  and  uni- 
form contraction  of  the  arteries  ;  but  it  may  be  regulated  by  the  power 
which  the  arteries  of  each  part  have,  in  their  muscular  tissue,  of  con- 
tracting so  as  to  diminish,  and  of  passively  dilating  or  yielding  so  as  to 
permit  an  increase  of  the  supply  of  blood,  according  to  the  requirements 
of  the  part  to  which  they  are  distributed.  And  thus,  while  the  ventricles 
of  the  heart  determine  the  total  quantity  of  blood,  to  be  sent  onwards  at 
each  contraction,  and  the  force  of  its  propulsion,  and  while  the  large 
and  merely  elastic  arteries  distribute  it  and  equalize  its  stream,  the 
smaller  arteries,  in  addition,  regulate  and  determine,  by  means  of  their 
muscular  tissue,  the  proportion  of  the  whole  quantity  of  blood  which 
shall  be  distributed  to  each  part. 

It  must  be  remembered,  however,  that  this  regulating  function  of  the 
arteries  is  itself  governed  and  directed  by  the  nervous  system  ^see  p.  145). 

Another  function  of  the  muscular  element  of  the  middle  coat  of  ar- 
teries is  (2),  to  co-operate  with  the  elastic  in  adapting  the  calibre  of  the 
vessels  to  the  quantity  of  blood  which  they  contain.  For  the  amount  of 
fluid  in  the  blood-vessels  varies  very  considerably  even  from  hour  to  hour, 
and  can  never  be  quite  constant;  and  were  the  elastic  tissue  only  pres- 
ent, the  pressure  exercised  by  the  walls  of  the  containing  vessels  on  the 
contained  blood  would  be  sometimes  very  small,  and  sometimes  inordi- 
nately great.  The  presence  of  a  muscular  element,  however,  provides  for 
a  certain  uniformity  in  the  amount  of  pressure  exercised;  and  it  is  by 
this  adaptive,  uniform,  gentle,  muscular  contraction,  that  the  normal 
tone  of  the  blood-vessels  is  maintained.  Deficiency  of  this  tone  is  the 
cause  of  the  soft  and  yielding  pulse,  and  its  unnatural  excess,  of  the  hard 
and  tense  one. 

The  elastic  and  muscular  contraction  of  an  artery  may  also  be  regarded 
as  fulfilling  a  natural  purpose  when  (3),  the  artery  being  cut,  it  first 
limits  and  then,  in  conjunction  with  the  coagulated  fibrin,  arrests  the 


THE    CIRCULATION    OF  THE    BLOOD.  137 

escape  of  blood.  It  is  only  in  consequence  of  such  contraction  and 
coagulation  that  we  are  free  from  danger  through  even  very  slight 
wounds;  for  it  is  only  when  the  artery  is  closed  that  the  processes  for  the 
more  permauent  and  secure  prevention  of  bleeding  are  established. 

(4)  There  appears  no  reason  for  supposing  that  the  muscular  coat  as- 
sists, to  more  than  a  very  small  degree,  in  propelling  the  onward  current 
of  blood. 

(1.)  When  a  small  artery  in  the  living  subject  is  exposed  to  the  air  or 
cold.,  it  gradually  but  manifestly  contracts.  Hunter  observed  that  the 
posterior  tibial  artery  of  a  dog  when  laid  bare,  became  in  a  short  time  so 
much  contracted  as  almost  to  prevent  the  transmission  of  blood;  and  the 
observation  has  been  often  and  variously  confirmed.  Simply  elasticity 
could  not  effect  this. 

(2.)  When  an  artery  is  cut  across,  its  divided  ends  contract,  and  the 
orifices  may  be  completely  closed.  The  rapidity  and  completeness  of 
this  contraction  vary  in  different  animals;  they  are  generally  greater  in 
young  than  in  old  animals;  and  less,  apparently,  in  man  than  in  the 
lower  animals.  This  contraction  is  due  in  part  to  elasticity,  but  in  part, 
also,  to  muscular  action;  for  it  is  generally  increased  by  the  application 
of  cold,  or  of  any  simple  stimulating  substances,  or  by  mechanically  irri- 
tating the  cut  ends  of  the  artery,  as  by  picking  or  twisting  them. 

(3.)  The  contractile  property  of  arteries  continues  many  hours  after 
death,  and  thus  affords  an  opportunity  of  distinguishing  it  from  their 
elasticity.  When  a  portion  of  an  artery  of  a  recently  killed  animal  is 
exposed,  it  gradually  contracts,  and  its  canal  may  be  thus  completely 
closed;  in  this  contracted  state  it  remains  for  a  time,  varying  from  a  few 
hours  to  two  days;  then  it  dilates  again,  and  permanently  retains  the 
same  size. 

The  Pulse. 

If  we  place  our  fingers  upon  the  radial  artery  at  the  wrist,  or  upon 
any  artery  of  the  body  which  is  sufficiently  superficial,  we  experience  a 
sensation  as  if  our  fingers  were  alternately  lifted  or  raised  up  from  the 
artery  and  allowed  to  fall  again,  and  this  action  is  repeated  very  fre- 
quently in  the  course  of  a  minute.  In  other  words  we  feel  the  pulse  of 
the  artery. 

The  pulse  is  generally  described  as  an  expansion  of  the  artery  pro- 
duced by  the  wave  of  blood  set  in  motion  by  the  injection  of  blood  into 
the  already  full  aorta  at  each  ventricular  systole. 

As  the  force  of  the  left  ventricle,  however,  is  not  expended  in  dilat- 
ing the  aorta  only,  the  wave  of  blood  passes  on,  expanding  the  arteries 
as  it  goes,  running  as  it  Avere  on  the  surface  of  the  more  slowly  travelling 
blood  already  contained  in  them,  and  producing  the  pulse  as  it  pro- 
ceeds. 

The  distention  of  each  artery  increases  both  its  length  and  its  diam- 
eter. In  their  elongation,  the  arteries  change  their  form,  the  straight 
ones  becoming  slightly  curved,  and  those  already  curved  becoming  more 


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so;  but  they  recover  their  previous  form  as  well  as  their  diameter  when 
the  ventricular  contraction  ceases,  and  their  elastic  walls  recoil.  The 
increase  of  their  curves  which  accompanies  the  distention  of  arteries,  and 
the  succeeding  recoil,  maybe  well  seen  in  the  prominent  temporal  artery 
of  an  old  person.  In  feeling  the  pulse,  the  finger  cannot  distinguish  the 
sensation  produced  by  the  dilatation  from  that  produced  by  the  elongation 
and  curving;  that  which  it  perceives  most  plainly,  however,  is  the  dila- 
tation, or  return,  more  or  less,  to  the  cylindrical  form,  of  the  artery  which 
has  been  partially  flattened  by  the  finger. 

The  pulse — due  to  any  given  beat  of  the  heart — is  not  perceptible  at 
the  same  moment  in  all  the  arteries  of  the  body.  Thus,  it  can  be  felt  in 
the  carotid  a  very  short  time  before  it  is  perceptible  in  the  radial  ar- 
tery, and  in  this  vessel  again  before  the  dorsal  artery  of  the  foot.  The 
delay  in  the  beat  is  in  proportion  to  the  distance  of  the  artery  from  the 
heart,  but  the  difference  in  time  between  the  beat  of  any  two  arteries 
never  exceeds  probably  ^  to  -J  of  a  second. 

A  distinction  must  be  carefully  made  between  the  passage  of  the  wave 
along  the  arteries  and  the  velocity  of  the  stream  (p.  156)  of  blood.  Both 
wave  and  current  are  present;  but  the  rates  at  which  they  travel  are  very 
different,  that  of  the  wave  16.5  to  33  feet  per  second  (5  to  10  metres), 
being  twenty  or  thirty  times  as  great  as  that  of  the  current. 

The  Sphygmograph. — A  great  deal  of  light  has  been  thrown  on 


BOTTOM 

Fig.  123.— Diagram  of  the  mode  of  action  of  the  Sphygmograph. 

what  may  be  called  the  form  of  the  pulse  wave  by  the  sphygmograph 
(Figs.  123  and  124).  The  principle  on  which  it  acts  is  very  simple  (see 
Fig.  123). 

The  small  button  replaces  the  finger  in  the  act  of  taking  the  pulse, 
and  is  made  to  rest  lightly  on  the  artery,  the  pulsations  of  which  it  is 
desired  to  investigate.  The  up-and-down  movement  of  the  button  is 
communicated  to  the  lever,  to  the  hinder  end  of  which  is  attached  a 
slight  spring,  which  allows  the  lever  to  move  up,  at  the  same  that  time  it 
is  just  strong  enough  to  resist  its  making  any  sudden  jerk,  and  in  the  in- 
terval of  the  beats  also  to  assist  in  bringing  it  back  to  its  original  position. 
For  ordinary  purposes  the  instrument  is  bound  on  the  wrist  (Fig.  124). 

It  is  evident  that  the  beating  of  the  pulse  with  the  reaction  of  the 
.spring  will  cause  an  up-and-down  movement  of  the  lever,  the  pen  of 


THE  CIRCULATION    OF    THE    BLOOD. 


139 


which  will  write  the  effect  on  a  smoked  card,  which  is  made  to  move  by 
clockwork  in  the  direction  of  the  arrow.     Thus  a  tracing  of  the  pulse  is 


Fig.  124.— The  Sphygmograph  applied  to  the  arm. 

obtained,  and  in  this  way  much  more  delicate  effects  can  be  seen  than 
can  be  felt  on  the  application  of  the  finger. 

The  tracing  of  the  pulse  {sphygmogram),  obtained  by  the  use  of  the 
sphygmograph,  differs  somewhat  according  to  the  artery  upon  which  it 
is  applied,  but  its  general  characters  are  much  the  same  in  all  cases.  It 
consists  of: — A  sudden  upstroke  (Fig.  125,  a),  which  is  somewhat  higher 
and  more  abrupt  in  the  pulse  of  the  carotid  and  of  other  arteries  near 
the  heart  than  in  the  radial  and  other  arteries  more  remote;  and  a 
gradual  decline  (b),  less  abrupt,  and  therefore  taking  a  longer  time  than 
(a).  It  is  seldom,  however,  that  the  decline  is  an  uninterrupted  fall;  it  is 
usually  marked  about  half-way  by  a  dis- 
tinct notch  (c),  called  the  dicrotic  notch, 
which  is  caused  by  a  second  more  or  less 
marked  ascent  of  the  lever  at  that  point 
by  a  second  wave  called  the  dicrotic 
leave  (d);  not  unfrequently  (in  which 
case  the  tracing  is  said  to  have  a  double 
apex)  there  is  also  soon  after  the  com- 
mencement of  the  descent  a  slight 
ascent  previous  to  the  dicrotic  notch: 
this  is  called  the  pre-dicrotic  wave  (c), 
and  in  addition  there  may  be  one  or  more 
slight  ascents  after  the  dicrotic,  called  post-dicrotic  (e). 

The  explanation  of  these  tracings  presents  some  difficulties,  not,  how- 
ever, as  regards  the  two  primary  factors,  viz.,  the  upstroke  and  down- 
stroke,  because  they  are  universally  taken  to  mean  the  sadden  injection 
of  blood  into  the  already  full  arteries,  and  that  this  passes  through  the 
artery  as  a  wave  and  expands  them,  the  gradual  fall  of  the  lever  signi- 
fying the  recovery  of  the  arteries  by  their  recoil.  It  may  be  demonstrated 
on  a  system  of  elastic  tubes,  where  a  syringe  pumps  in  water  at  regular 
intervals,  just  as  well  as  on  the  radial  artery,  or  on  a  more  complicated 
system  of  tubes  in  which  the  heart,  the  arteries,  the  capillaries  and  veins 
are  represented,  which  is  known  as  an  arterial  schema.     If  we  place  two 


Fig.  l-'5.  -  Diagram  of  pulse-tracing. 
A,  upstroke;  b,  downstroke:  c,  pre-cli- 
crotic  wave;  d,  dicrotic;  b,  post-dicrotic 
wave. 


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HANDBOOK   OF   PHYSIOLOGY. 


or  more  sphygmographs  upon  such  a  system  of  tubes  at  increasing  dis- 
tances from  the  pump,  we  may  demonstrate  that  the  rise  of  the  lever 
commences  first  in  that  nearest  the  pump,  and  is  higher  and  more  sud- 
den, while  at  a  longer  distance  from  the  pump  the  wave  is  less  marked, 
and  a  little  later.  So  in  the  arteries  of  the  body  the  wave  of  blood 
gradually  gets  less  and  less  as  we  approach  the  periphery  of  the  arterial 
system,  and  is  lost  in  the  capillaries.  By  the  sudden  injection  of  blood 
two  distinct  waves  are  produced,  which  are  called  the  tidal  and  percus- 


Fig.  136.— Diagram  of  the  formation  of  the  pulse -traciDg.    a,  percussion  wave;  b,  tidal  wave: 
c,  dicrotic  wave.    (Mahomed.) 

sion  waves.  The  tidal  wave  occurs  whenever  fluid  is  injected  into  an 
elastic  tube  (Fig.  126,  b),  and  is  due  to  the  expansion  of  the  tube  and  its 
more  gradual  collapse.  The  percussion  wave  occurs  (Fig.  126,  a)  when 
the  impulse  imparted  to  the  fluid  is  more  sudden;  this  causes  an  abrupt 


Fig.  127.  —Pulse-tracing  of  radial  artery,  somewhat  deficient  in  tone.    (Sanderson.) 

upstroke  of  the  lever,  which  then  falls  until  it  is  again  caught  up 
perhaps  by  the  tidal  wave  which  begins  at  the  same  time,  but  is  not  so 
quick. 

In  this  way,  generally  speaking,  the  apex  of  the  upstroke  is  double; 
the  second  upstroke,  the  so-called  pre-dicrotic  elevation  of  the  lever, 
representing  the  tidal  wave.  The  double  apex  is  most  marked  in  trac- 
ing from  large  arteries,  especially  when  their  tone  is  deficient.  In 
tracings,  on  the  other  hand,  from  arteries  of  medium  size,  e.  g.,    the 


THE    CIRCULATION    OF    THE    BLOOD.  141 

radial,  the  upstroke  is  usually  single.  In  this  case  the  percussion-im- 
pulse is  not  sufficiently  strong  to  jerk  up  the  lever  and  produce  an  effect 
distinct  from  that  of  the  systolic  wave  which  immediately  follows  it, 
and  which  continues  and  completes  the  distention.  In  cases  of  feeble 
arterial  tension,  however,  the  percussion-impulse  may  be  traced  by  the 


Fig.  128.— Pulse-tracing  of  radial  artery,  with  double  apex.    CSanderson.) 

sphygmograph,  not  only  in  the  carotid  pulse,  but  to  a  less  extent  in  the 
radial  also  (Fig.  128). 

The  interruptions  in  the  downstroke  are  called  the  Tcatacrotic  waves, 
to  distinguish  them  from  an  interruption  in  the  upstroke,  called  the 


Fig.  129.—  Anacrotic  pulse  from  a  case  of  aortic  aneurism,    a,  anacrotic  wave  (or  percussion 
wave),    b,  tidal  or  pre-dicrotic  wave,  continued  rise  in  tension  (or  higher  tidal  wave). 

anacrotic  wave,  which  is  occasionally  met  with  in  cases  in  which  the 
pre-dicrotic  or  tidal  wave  is  higher  than  the  percussion  wave. 

There  is  considerable  difference  of  opinion  as  to  whether  the  dicrotic 
wave  is  generally  present  in  health,  and  also  as  to  its  cause.  The 
balance  of  opinion,  however,  appears  to  be  in  favor  of  the  belief  that 
the  dicrotic  wave  is  present  in  health,  although  it  may  be  very  faint ; 
while  in  certain  conditions  not  necessarily  diseased,  it  becomes  so  marked 
as  to  be  quite  plain  to  the  unaided  fiuger.  Such  a  pulse  is  called  dicro- 
tic. Sometimes  the  dicrotic  rise  exceeds  the  initial  upstroke,  and  the 
pulse  is  then  called  liy  per  dicrotic. 

As  to  the  cause  of  dicrotism,  one  opinion  (1)  is  that  it  is  due  to  a  re- 
covery of  pressure  during  the  elastic  recoil,  in  consequence  of  a  rebound 
from  the  periphery.  It  may  indeed  be  produced  on  a  schema  by  ob- 
structing the  tube  at  a  little  distance  beyond  the  spot  where  the  sphygmo- 
graph  is  placed.  Against  this  view,  however,  is  the  fact  that  the  notch 
appears  at  about  the  same  point  in  the  downstroke  in  tracings  from  the 
carotid  and  from  the  radial,  and  not  first  in  the  radial  tracing,  as  it  should 
do,  if  this  theory  was  correct,  since  that  artery  is  nearer  the  periphery 
than  the  carotid,  aud  as  it  does  in  the  corresponding  experiment  with 
the  arterial  schema  when  the  tube  is  obstructed.     (2)  The  generally  ac- 


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cepted  notion  among  clinical  observers,  is  that  the  dicrotic  wave  is  due 
to  the  rebound  from  the  aortic  valves  which  causes  a  second  wave;  but 
the  question  cannot  be  considered  settled,  and  the  presence  of  marked 

dicrotism  in  cases  of  hemorrhage, 
of  anaemia,  and  of  other  weaken- 
ing conditions,  as  well  as  its  pres- 
ence in  cases  of  diminished  pres- 
sure within  the  arteries,  would 
imply  that  it  might,  at  any  rate 
sometimes,  be  due  to  the  altered 
specific  gravity  of  the  blood  within 
the  vessels,  either  directly  or 
through  the  indirect  effect  of  these 
conditions  on  the  tone  of  the  arte- 
rial walls. 

Waves  may  be  produced  in  any 
elastic  tube  when  a  fluid  is  being 
driven  through  it  with  an  inter- 
mittent force,  such  waves  being 
called  waves  of  oscillation  (M.  Fos- 
ter). Their  origin  has  received 
various  explanations.  In  an  arte- 
rial schema  they  vary  with  the  spe- 
cific gravity  of  the  fluid  used,  and 
with  the  kind  of  tubing,  and  may 
be  therefore  supposed  to  vary  in 
the  body  with  the  condition  of  the 
blood  and  of  the  arteries. 

Some  consider  the  secondary 
waves  in  the  downstroke  of  a  nor- 
mal tracing  to  be  oscillation  waves; 
but,  as  just  mentioned,  even  if 
this  be  the  case,  as  is  most  likely 
with  post-dicrotic  waves,  the  dicro- 
tic wave  itself  is  almost  certainly  due  to  the  rebound  from  the  aortic 
valves. 

The  anacrotic  notch  is  usually  associated  with  disease  of  the  arteries, 
e.  g.,  in  atheroma  and  aneurism.  The  dicrotic  notch  is  called  diastolic 
or  aortic,  and  in  point  of  time  indicates  the  closure  of  the  aortic  valves. 
Of  the  three  main  parts  then  of  a  pulse  tracing,  viz.,  the  percussion 
wave,  the  tidal,  and  the  dicrotic,  the  percussion  wave  is  produced  by 
sudden  and  forcible  contraction  of  the  heart,  perhaps  exaggerated  by  an 
excited  action,  and  may  be  transmitted  much  more  rapidly  than  the 
tidal  wave,   and  so  the  two  may  be  distinct  ;  frequently,  however,  they 


Fig.  130. — Diagrams  of  pulse  curves  with 
exaggeration  of  one  or  other  of  the  three  waves. 
A,  percussion;  b,  tidal;  c,  dicrotic.  1,  percus- 
sion wave  very  marked;  2,  tidal  wave  sudden; 
3,  dicrotic  pulse  curve;  4,  and  5,  the  tidal  wave 
very  exaggerated,  from  high  tension.  (Maho- 
med.) 


THE   CIRCULATION    OF   THE    BLOOD.  143 

are  inseparable.  The  dicrotic  wave  may  be  as  great  or  greater  than  the 
other  two. 

According  to  Mahomed,  the  distinctness  of  the  three  waves  depends 
upon  the  following  conditions  : — 

The  percussion  wave  is  increased  by  : — 1.  Forcible  contraction  of  the 
Heart ;  2.  Sudden  contraction  of  the  Heart ;  3.  Large  volume  of  blood; 
4.  Fulness  of  vessel  ;  and  diminished  by  the  reversed  conditions. 

The  tidal  wave  is  increased  by: — 1.  Slow  and  prolonged  contraction 
of  the  Heart ;  2.  Large  volume  of  blood  ;  3.  Comparative  emptiness  of 
vessels  ;  4.  Diminished  outflow  or  slow  capillary  circulation  ;  and  dimin- 
ished by  the  reverse  conditions. 

The  dicrotic  wave  is  increased  by  : — 1.  Sudden  contraction  of  the 
Heart  ;  2.  Low  blood  pressure  ;  3.  Increased  outflow  or  rapid  capillary 
circulation;  4.  Elasticity  of  the  aorta  ;  5.  Eelaxation  of  muscular  coat ; 
and  diminished  by  the  reversed  conditions. 

One  very  important  precaution  in  the  use  of  the  sphygmograph  lies 
in  the  careful  regulation  of  the  pressure.  If  the  pressure  be  too  great, 
the  characters  of  the  pulse  may  be  almost  entirely  obscured,  or  the  ar- 
tery may  be  entirely  obstructed,  and  no  tracing  is  obtained  ;  and  on  the 
other  hand,  if  the  pressure  be  too  slight,  a  very  small  part  of  the  charac- 
ers  may  be  represented  on  the  tracing. 

The   Pressure   of  the   Blood    within  the    Arteries    (producing 

arterial   tension). 

It  will  be  understood  from  all  that  has  been  said  about  the  ar- 
teries in  a  normal  condition  (a)  that  they  are  during  life  continually 
"on  the  stretch,"  even  during  the  cardiac  diastole,  and  that  in  con- 
sequence of  the  injection  of  more  blood  at  each  systole  of  the  ven- 
tricle into  the  elastic  aorta,  that  this  stretched  condition  is  exagge- 
rated each  time  the  ventricle  empties  itself.  This  state  of  distention 
of  the  arteries  is  due  to  the  pressure  of  blood  within  them,  and 
arises  in  consequence  of  the  resistance  presented  by  the  smaller  arteries 
and  capillaries  (peripheral  resistance)  to  the  sudden  emptying  of  the  ar- 
terial system  between  the  contractions  of  the  ventricle.  It  is  called  the 
condition  of  arterial  tension.  It  will  be  further  understood  (b)  that,  as 
the  blood  is  forcibly  injected  into  the  already  full  arteries  against  their 
elasticity,  it  must  be  subjected  to  the  pressure  of  the  arterial  walls,  so 
that,  when  an  artery  is  cut  across,  the  blood  is  projected  forwards  by 
this  force  for  a  considerable  distance.  Thus,  although  the  blood  distends 
the  arteries  and  produces  tension,  yet  the  elasticity  of  the  arteries  reacts 
upon  the  blood,  and  subjects  it  to  pressure.  We  have  therefore  to  remem- 
ber that  we  have  to  do  with  two  things  related  but  not  identical,  viz.,  the 
pressure  which  the  blood  exerts  upon  the  arterial  walls  tending  to  stretch 
them,  and  the  pressure  to  which  the  blood  is  subject  by  the  arteries  tend- 


144 


HANDBOOK    OF    PHYSIOLOGY. 


ing  to  drive  it  on  in  the  direction  of  least  resistance.     The  only  direction 
in  which  it  can  be  driven  is  onwards  towards  the  capillaries,  and  so  the 

blood-pressure  in  the  arteries  is  one  of  the 
great  agents  in  maintaining  the  circulation. 
The  relations  which  exist  between  the 
arteries  and  their  contained  blood  are  thus 
so  obviously  of  importance  to  the  carrying 
on  of  the  criculation,  that  it  becomes  neces- 
sary to  be  able  to  gauge  the  alterations  in 
blood -pressure  very  accurately.  This  may  be 
done  by  means  of  a  mercurial  manometer  in 
the  following  way: — The  short  horizontal 
limb  of  this  (Fig.  131)  is  connected,  by 
means  of  an  elastic  tube  and  canula,  with 
the  interior  of  an  artery;  a  solution  of  sodium 
or  potassium  carbonate  being  previously  in- 
troduced into  this  part  of  the  apparatus  to 
prevent  coagulation  of  the  blood.  The 
blood-pressure  is  thus  communicated  to  the 
upper  part  of  the  mercurial  column;  and  the 
depth  to  which  the  latter  sinks,  added  to  the 
height  xo  which  it  rises  in  the  other,  will 
give  the  height  of  the  mercurial  column 
which  the  blood-pressure  balances;  the 
weight  of  the  soda  solution  being  subtracted. 
For  the  estimation  of  the  arterial  tension  at  any  given  moment,  no 
further  apparatus  than  this,  which  is  called  Poiseuilles's  hcemadynamo- 
meter,  is  necessary;  but  for  noting  the  variations  of  pressure  in  the  ar- 
terial system,  as  well  as  its  absolute  amount,  the  instrument  is  usually 
combined  with  a  registering  apparatus,  and  in  this  form  is  called  a  kymo- 
graph. 

The  kymograph,  invented  by  Ludwig,  is  composed  of  a  hasmadyna- 
mometer,  the  open  mercurial  column  of  which  supports  a  floating  piston 
and  vertical  rod,  with  short  horizontal  pen  (Fig.  132).  The  pen  is 
adjusted  in  contact  with  a  sheet  of  paper,  which  is  caused  to  move  at  a 
uniform  rate  by  clockwork;  and  thus  the  up-and-down  movements  of  the 
mercurial  column,  which  are  communicated  to  the  rod  and  pen,  are 
marked  or  registered  on  the  moving  paper,  as  in  the  registering  appa- 
ratus of  the  sphygmograph,  and  minute  variations  are  graphically  re- 
corded (Fig.  134). 

For  some  purposes  the  spring  kymograph  of  Fick  (Fig.  135)  is  pref- 
erable to  the  mercurial  kymograph.  It  consists  of  a  hollow  C-shaped 
spring,  filled  with  fluid,  the  interior  of  which  is  brought  into  connection 
with  the  interior  of  an  artery,  by  means  of  a  flexible  metallic  tube  and 


Fig.  131.— Diagram  of  mercu 
rial  manometer. 


THE    CIRCULATION    OF  THE    BLOOD. 


14,5 


canula.     In  response  to   the  pressure   transmitted   to  its  interior,  the 
spring,  c,  tends  to  straighten  itself,  and  the  movement  thus  produced  is 


Fig.  132. 


Fig.  133. 


Fig.  139.— Diagram  of  mercurial  kymograph,  a,  revolving  cylinder,  worked  by  a  clockwork 
arrangement  contained  in  the  box  (b).  the  speed  being  regulated  by  a  fan  above  the  box;  cylinder 
supported  by  an  upright  (b),  and  capable  of  being  raised  or  lowered  by  a  screw  (o),  by  a  handle  at- 
tached to  it;  d,  c,  E,  represent  mercurial  manometer,  a  somewhat  different  form  of  which  is  shown 
in  next  figure. 

Fig.  133.  Diagram  of  mercurial  manometer,  a.  Floating  rod  and  pen.  6.  Tube,  which  com- 
municates with  a  bottle  containing  an  alkaline  solution,  c.  Elastic  tube  and  canula;  d,  the  latter 
being  intended  for  insertion  in  an  artery. 

communicated  hy  means  of  a  lever,  b,  to  a  writing-needle  and  registering 
apparatus. 


Fig.  134.— Normal  tracing  of  arterial  pressure  in  the  rabbit  obtained  with  the  mercurial  kymo- 
graph. The  smaller  undulations  correspond  with  the  heart  beats;  the  larger  curves  with  the 
respiratory  movements.     (  Burdon-Sanderson.) 

Fig.  13G  exhibits  an  ordinary  arterial  pulse-tracing,  as  obtained  by 
the  spring  kymograph. 

From  observations  which  have  been  made  by  means  of  the  mercurial 
10 


146 


HANDBOOK    OF    PHYSIOLOGY. 


manometer,  it  has  been  found  that  the  pressure  of  blood  in  the  carotid 
of  a  rabbit  is  capable  of  supporting  a  column  of  2  to  3^  inches  (50  to  90 
mm.),  of  mercury,  in  the  dog  4  to  7  inches  (100  to  175  mm.),  in  the 
horse  5  to  8  inches  (150  to  200  mm.),  and  in  man  the  pressure  is  esti- 
mated to  be  about  the  same. 

To  measure  the  absolute  amount  of  this  pressure  in  any  artery,  it  is 
necessary  merely  to  multiply  the  area  of  its  transverse  section  by  the 
height  of  the  column  of  mercury  which  is  already  known  to  be  supported 


Fig.  135.— A  form  of  Fick's  Spring  Kymograph,  a,  tube  to  be  connected  with  artery;  c,  hollow- 
spring,  the  movement  of  which  moves  b,  the  writing  lever;  e,  screw  to  regulate  height  of  b;  d,  out- 
side protective  spring;  g,  screw  to  fix  on  the  upright  of  the  support. 

by  the  blood-pressure  in  any  part  of  the  arterial  system.  The  weight  of 
a  column  of  mercury  thus  found  will  represent  the  pressure  of  the  blood. 
Calculated  in  this  way,  the  blood-pressure  in  the  human  aorta  is  equal  to 
4  lb.  4  oz.  avoirdupois;  that  in  the  aorta  of  the  horse  being  11  lb.  9  oz.; 
and  that  in  the  radial  artery  at  the  human  wrist  only  4  drs.  Supposing 
the  muscular  power  of  the  right  ventricle  to  be  only  one-half  that  of  the 
left,  the  blood-pressure  in  the  pulmonary  artery  will  be  only  2  lb.  2  oz. 
avoirdupois.  The  amounts  above  stated  represent  the  arterial  tension  at 
the  time  of  the  ventricular  contraction. 

The  blood-pressure  is  greatest  in  the  left  ventricle  and  at  the  be- 
ginning of  the  aorta,  and  decreases  toward  the  capillaries.  It  is  greatest 
in  the  arteries  at  the  period  of  the  ventricular  systole,  and  is  least  in  the 
auricles,  during  diastole,  when  the  pressure  there  and  in  the  great  veins 
becomes,  as  we  have  seen,  negative.     The  mean  arterial  pressure  equals 


THE    CIRCULATION    OF   THE    BLOOD.  147 

the  average  of  the  pressures  in  all  the  arteries.  The  pressure  in  the 
veins  is  never  more  than  one  tenth  of  the  pressure  in  the  corresponding 
arteries,  and  is  greatest  at  the  time  of  auricular  systole.  There  is  no 
periodic  variation  in  venous  pressure,  as  there  is  in  the  arterial,  except  in 
the  great  veins. 

Variations  of  Blood-Pressure. — Many  circumstances  cause  con- 
siderable variations  in  the  amount  of  the  blood-pressure.  The  following 
are  the  chief :— (1)  Changes  in  the  beat  of  the  Heart;  (2)  Changes  in  the 


Fig.  136.— Normal  arterial  traciDg  obtained  with  Fick's  kymograph  in  the  dog.  (Burdon-San- 
derson.) 

Arteries  and  Capillaries  ;  (3)  Changes  due  to  Nerve  Action;  (4)  Changes 
in  the  Blood;  (5)  Respiratory  Changes. 

1.  Changes  in  the  Beat  of  the  Heart. — The  systole  and  diastole  of  the 
muscular  chambers.  The  arterial  tension  increases  during  systole  and 
diminishes  during  diastole.  The  greater  the  frequency,  moreover,  of  the 
heart's  contractions,  the  greater  is  the  blood-pressure,  cmteris  paribus. 
As  a  rule,  however,  when  the  heart  contracts  frequently,  the  beats  lose 
in  strength,  and  the  increase  in  frequency  may  be  compensated  for  by 
the  delivery  into  the  arteries  at  each  beat  of  a  comparatively  small  quan- 
tity of  blood.  The  greater  the  quantity  of  blood  expelled  from  the  heart 
at  each  contraction  the  greater  is  the  blood-pressure. 

The  quantity  and  quality  of  the  blood  nourishing  the  heart's  sub- 
stance through  the  coronary  arteries  must  exercise  also  a  very  consider- 
able influence  upon  its  action,  and  therefore  upon  the  blood-pressure. 

2.  Changes  in  the  Arteries  and  Capillaries. — Variations  in  the  degree 
of  contraction  of  the  smaller  arteries  modify  the  blood-pressure  by  favor- 
ing or  impeding  the  accumulation  of  blood  in  the  arterial  system  which 
follows  every  contraction  of  the  heart;  the  contraction  of  the  arterial 
Avails  increasing  the  blood-pressure,  and  their  relaxation  lowering  it. 

3.  Changes  due  to  Nerve  Action. — The  nervous  system  has  a  very 
important  action  in  regulating  the  blood-pressure.  Its  influence  is 
exerted  chiefly  upon  the  muscular  coat  of  the  arteries  and  not  upon  the 
elastic  element,  which  possesses,  as  must  be  obvious,  rather  physical  than 
vital  properties.  The  muscular  tissue  in  the  walls  of  the  vessels  increases 
in  amount  relatively  to  the  other  coats  as  the  arteries  grow  smaller,  so 
that  in  the  smallest  arteries  it  is  developed  out  of  all  proportion  to  the 
other  elements;  in  fact,  in  passing  from  capillary  vessels,  made  up  as  we 
have  seen  of  endothelial  cells  with  a  ground  substance,  the  first  change 


148  HANDBOOK    OF    PHYSIOLOGY. 

which  occurs  as  the  vessels  become  larger  (on  the  side  of  the  arteries)  is 
the  appearance  of  muscular  fibres.  Thus  the  nervous  system  is  more 
powerful  in  regulating  the  calibre  of  the  smaller  than  of  the  larger 
arteries. 

It  was  long  ago  shown  by  Claude  Bernard  that  if  the  cervical  sympa- 


Fig.  137.  —  Plethysmograph.  By  means  of  this  apparatus,  the  alteration  in  volume  of  the  arm, 
e,  which  is  inclosed  in  a  glass  tube,  a,  filled  with  fluid,  the  opening  through  which  it  passes  being 
firmly  closed  by  a  thick  gutta-percha  band,  f,  is  communicated  to  the  lever,  e,  and  registered 
by  a  recording  apparatus.  The  fluid  in  a  communicates  with  that  in  b,  the  upper  limit  of  which  is 
above  that  in  A.  The  chief  alterations  in  volume  are  due  to  alteration  in  the  blood  contained  in  the 
arm.  When  the  volume  is  increased,  fluid  passes  out  of  the  glass  cylinder,  and  the  lever,  d,  also  is 
raised,  and  when  a  decrease  takes  place  the  fluid  returns  again  from  b  and  A.  It  will  therefore  be 
evident  that  the  apparatus  is  capable  of  recording  alterations  of  blood-pressure  in  the  arm.  Ap- 
paratus founded  upon  the  same  principle  have  been  used  for  recording  alterations  in  the  volume 
of  the  spleen  and  kidney. 

thetic  nerve  is  divided  in  a  rabbit,  the  blood-vessels  of  the  corresponding 
side  of  tbe  head  and  neck  become  dilated.  This  effect  is  best  seen  in 
the  ear,  which  if  held  up  to  the  light  is  seen  to  become  redder,  and  the 
arteries  are  seen  to  become  larger.  The  whole  ear  is  distinctly  warmer 
than  the  opposite  one.  This  effect  is  produced  by  removing  the  arteries 
from  the  influence  of  the  central  nervous  system,  which  influence  nor- 
mally passes  down  the  divided  nerve;  for  if  the  peripheral  end  of  the 
divided  nerve  (i.  e.,  that  farthest  from  the  brain)  be  stimulated,  the 
arteries  which  were  before  dilated  return  to  their  natural  size,  and  the 
parts  regain  their  primitive  condition.  And,  besides  this,  if  the  stimu- 
lus which  is  applied  is  too  strong  or  too  long  continued,  the  point  of 
normal  constriction  is  passed,  and  the  vessels  become  much  more  con- 
tracted than  normal.  The  natural  condition,  which  is  somewhere  about 
midway  between  extreme  contraction  and  extreme  dilatation,  is  called 
the  natural  tone  of  an  artery,  and  if  this  is  not  maintained,  the  vessel  is 
said  to  have  lost  tone,  or  if  it  is  exaggerated,  the  tone  is  said  to  be  too 
great.  The  influence  of  the  nervous  system  upon  the  vessels  consists  in 
maintaining  a  natural  tone.  The  effects  described  as  having  been  pro- 
duced by  section  of  the  cervical  sympathetic  and  by  subsequent  stimula- 
tion are  not  peculiar  to  that  nerve,  as  it  has  been  found  that  for  every 
part  of  the  body  there  exists  a  nerve  the  division  of  which  produces  the 


THE    CIRCULATION    OF   THE    BLOOD.  149 

same  effects,  viz.,  dilatation  of  the  arteries;  such  may  be  cited  as  the  case 
with  the  sciatic,  the  splanchnic  nerves,  and  the  nerves  of  the  brachial 
plexus:  when  these  are  divided,  dilatation  of  the  blood-vessels  in  the 
parts  supplied  by  them  takes  place.  It  appears,  therefore,  that  nerves 
exist  which  have  a  distinct  control  over  the  vascular  supply  of  every  part 
of  the  body. 

These  nerves  are  called  vaso-motor  ;  they  run  now  in  cerebro-spinal, 
now  in  the  sympathetic  nerve-trunks. 

Vaso-motor  centres. — Experiments  by  Ludwig  and  others  show  that 
the  vaso-motor  fibres  come  primarily  from  gray  matter  (vaso-motor  centre) 
in  the  interior  of  the  medulla  oblongata,  between  the  calamus  scriptoriits 
and  the  corpora  quadrigemina.  Thence  the  vaso-motor  fibres  pass  down 
in  the  interior  of  the  spinal  cord,  and  issuing  with  the  anterior  roots  of 
the  spinal  nerves,  traverse  the  various  ganglia  on  the  prae-vertebral  cord 
of  the  sympathetic,  and,  accompanied  by  branches  from  those  ganglia, 
pass  to  their  distination. 

Secondary  or  subordinate  centres  exist  in  the  spinal  cord,  and  local 
centres  in  various  regions  of  the  body,  and  through  these,  directly,  under 
ordinary  circumstances,  vaso-motor  changes  are  also  effected. 

The  influence  exerted  by  the  chief  vaso-motor  centre  is  not  only  in 
constant  moderate  action,  but  maybe  altered  in  several  ways,  but  chief! v 
by  afferent  (sensory)  stimuli.  These  stimuli  may  act  in  two  ways,  either 
increasing  or  diminishing  the  usual  action  of  the  centre,  which  maintains 
a  medium  tone  of  the  arteries.  This  afferent  influence  upon  the  centre 
may  be  extremely  well  shown  by  the  action  of  a  nerve  the  existence  of 
which  was  demonstrated  by  Cyon  and  Ludwig,  and  which  is  called  the 
depressor,  because  of  its  characteristic  influence  on  the  blood-pressure. 

Depressor  Nerve. — This  small  nerve  arises,  in  the  rabbit,  from  the 
superior  laryngeal  branch,  or  from  this  and  the  trunk  of  the  pneumogas- 
tric  nerve,  and  after  communicating  with  filaments  of  the  inferior  cer- 
vical ganglion  proceeds  to  the  heart. 

If  during  an  observation  of  the  blood-pressure  of  a  rabbit  this  nerve 
be  divided,  and  the  central  end  (i.  e.,  that  nearest  the  brain)  be  stimu- 
lated, a  remarkable  fall  of  blood-pressure  ensues  (Fig.  138). 

The  cause  of  the  fall  of  blood-pressure  is  found  to  proceed  from  the 
dilatation  of  the  vascular  district  within  the  abdomen  supplied  by  the 
splanchnic  nerves,  in  consequence  of  which  it  holds  a  much  larger  quan- 
tity of  blood  than  usual.  The  engorgement  of  the  splauchnic  area  very 
greatly  diminishes  the  blood  in  the  vessels  elsewhere,  and  so  materially 
diminishes  the  blood-pressure.  The  function  of  the  depressor  nerve  is 
presumed  to  be  that  of  conveying  to  the  vaso-motor  centre  indications 
of  such  conditions  of  the  heart  as  require  a  diminution  of  the  tension  in 
the  blood-vessels  ;  as,  for  example,  that  the  heart  cannot,  with  sufficient 
ease,  propel  blood  into  the  already  too  full  or  too  tense  arteries. 


150  HANDBOOK    OF  PHYSIOLOGY. 

The  action  of  the  depressor  nerve  illustrates  a  somewhat  unusual 
effect  of  afferent  impulses,  as  it  causes  an  inhibition  of  the  vaso-motor 
centre.  As  a  rule,  the  stimulation  of  the  central  end  of  an  afferent 
nerve  produces  a  reverse  effect,  or,  in  other  words,  increases  the  tonic 
influence  of  the  centre,  and  by  causing  considerable  constriction  of  cer- 
tain arterioles,  either  locally  or  generally,  increases  the  blood-pressure. 
Thus  the  effect  of  stimulating  an  afferent  nerve  may  be  either  to  dilate 
or  to  constrict  the  arteries.  Stimulation  of  an  afferent  nerve  too  may 
produce  a  kind  of  paradoxical  effect,  causing  general  vascular  constric- 
tion and  so  general  increase  of  blood-pressure,  but  at  the  same  time  local 


Fig.  138.—  Tracing  showing  the  effect  on  blood-pressure  of  stimulating  the  central  end  of  the 
Depressor  nerve  in  the  rabbit.  To  be  read  from  right  to  left,  t,  indicates  the  rate  at  which  the  record- 
ing-surface was  travelling,  the  intervals  correspond  to  seconds;  c.  the  moment  of  entrance  of  cur- 
rent; 0,  moment  at  which  it  was  shut  off.  The  effect  is  some  time  in  developing  and  lasts  after 
the  current  has  been  taken  off.  The  larger  undulations  are  the  respiratory  curves;  the  pulse  oscil- 
lations are  very  small.    ( M.  Foster.) 

dilatation  which  must  evidently  have  an  immense  influence  in  increasing 
the  flow  of  blood  through  the  part. 

Not  only  may  the  vaso-motor  centre  be  reflexly  affected,  but  it  may 
also  be  affected  by  impulses  proceeding  to  it  from  the  cerebrum,  as  in  the 
case  of  blushing  from  mind  disturbance,  or  of  pallor  from  sudden  fear. 
It  will  be  shown,  too,  in  the  chapter  on  Respiration  that  the  circulation 
of  deoxygenated  blood  may  directly  stimulate  the  centre  itself. 

Local  Tonic  Centres. — Although  the  tone  of  the  arteries  is  influ- 
enced by  the  centres  in  the  cerebro-spinal  axis,  certain  experiments  prove 
that  this  is  not  the  only  way  in  which  it  may  be  influenced.  Thus  the 
dilatation  which  occurs  after  section  of  the  cervical  sympathetic  in  the 
first  experiment  cited  above,  only  remains  for  a  short  time,  and  is  soon 
followed — although  a  portion  of  the  nerve  may  have  been  removed  en- 
tirely— by  the  vessels  regaining  their  ordinary  calibre;  and  afterwards 
local  stimulation,  e.  g.,  the  application  of  heat  or  cold,  will  cause  dilata. 
tion  or  constriction.  From  this  it  is  probable  that  there  exists  a  distinct 
local  mechanism  for  each  vascular  area,  and  that  the  influence  exerted  by 


THE    CIRCULATION    OF    THE   BLOOD.  151 

the  central  nervous  system  acts  through  it  much  in  the  same  way  as  the 
cardio-inhibitory  centre  in  the  medulla  acts  upon  the  heart  through  the 
ganglia  contained  within  its  muscular  substance.  Central  impulses  may 
inhibit  or  increase  the  action  of  the  local  centres,  which  may  be  consid- 
ered to  be  sufficient  under  ordinary  circumstances  to  maintain  the  tone 
of  the  vessels.  The  observations  upon  the  functions  of  the  vaso-motor 
nerves  themselves  appear  to  divide  them  into  four  classes:  (1)  those  on 
division  of  which  dilatation  occurs  for  some  time,  and  which  on  stimu- 
lation of  their  peripheral  ends  produce  constriction;  (2)  those  on  division 
of  which  momentary  dilatation  followed  by  constriction  occurs,  with 
dilatation  on  stimulation;  (3)  those  on  division  of  which  dilatation  is 
caused,  which  lasts  for  a  limited  time,  with  constriction  if  stimulated  at 
once,  but  dilatation  if  some  time  is  allowed  to  elapse  before  the  stimula- 
tion is  applied;  (4)  a  class,  division  of  which  produces  no  effect  but 
which,  on  stimulation,  cause  according  to  their  function  either  dilata- 
tion or  constriction.  A  good  example  of  this  fourth  class  is  afforded  by 
the  nerves  supplying  the  submaxillary  gland,  viz.,  the  chorda  tympani 
and  the  sympathetic.  When  either  of  these  nerves  is  simply  divided,  no 
change  takes  place  in  the  vessels  of  the  glands;  but  on  stimulating  the 
chorda  tympani  the  vessels  dilate,  and,  on  the  other,  hand,  when  the 
sympathetic  is  stimulated  the  vessels  contract.  The  nerves  acting  like 
the  chorda  tympani  in  this  case  are  called  vaso-dilators,  and  those  like  the 
sympathetic  vaso-constrictors.  The  third  class,  which  produce  at  one 
time  dilatation,  at  another  time  constriction,  are  believed  to  contain  both 
kinds  of  vaso-motor  nerve-fibres,  or  to  act  as  dilators  or  contractors 
according  to  the  condition  of  the  local  apparatus.  It  is  probable  that 
all  of  these  nerves  act  by  inhibiting  or  augmenting  the  action  of  the  local 
nervous  mechanism  already  referred  to;  and  as  they  are  in  connection 
with  the  central  nervous  system,  it  is  through  them  that  the  medullary 
and  spinal  centres  are  capable  of  altering  or  of  maintaining  the  normal 
local  tone. 

It  may  also  be  supposed  that  the  local  nerve-centres  themselves  may 
be  directly  affected  by  the  condition  of  blood  nourishing  them. 

The  following  table  may  serve  as  a  summary  of  the  effect  of  the 
nervous  system  upon  the  arteries  and  so  upon  the  blood-pressure: — 

A.  An  increase  of  the  blood-pressure  may  be  produced  : — 

(1.)  By  stimulation  of  the  vaso-motor  centre  in  medulla,  either 

a.  Directly,  as  by  carbonated  or  deoxygenated  blood. 

fi.  Indirectly,  by  impressions  descending  from  the  cere- 
brum, e.  g.,  in  sudden  pallor. 

y.   Reflexly,  by  stimulation  of  sensory  nerves  anywhere. 
(2.)  By  stimulation  of  the  centres  in  spinal  cord. 

Possibly  directly  or  indirectly,  certainly  reflexly. 
(3.)  By  stimulation  of  the  local  centres  for  each  vascular  area, 


152  HANDBOOK    OF   PHYSIOLOGY. 

by  the  vaso-constrictor  nerves,  or  directly  by  means  of 
altered  blood. 

B.  A  decrease  of  the  blood-pressure  may  be  produced  : — 

(1.)  By  stimulation  of  the  vaso-motor  centre  in  medulla,  either 
(a.)  Directly,  as  by  oxygenated  or  aerated  blood. 
(/?.)  Indirectly,  by  impressions  descending  from  the  cere- 
brum— e.  g.,  in  blushing. 
(y.)  Reflexly,  by  stimulation  of  the  depressor  nerve,  and 
consequent   dilatation   of  vessels   of   splanchnic 
area,    and  possibly  by  stimulation  of  other  sen- 
sory nerves,  the  sensory  impulse  being  interpreted 
as  an  indication  for  diminished  blood-pressure. 
(2.)  By  stimulation  of  the  centres  in  spinal  cord.     Possibly  di- 

rectty,  indirectly  or  reflexly. 
(3.)  By  stimulation  of  local  centres  for  each  vascular  area  by 
the  vaso-dilator  nerve,  or  directly  by  means  of  altered 
blood 

4.  Clianges  in  the  blood. — a.  As  regards  quantity.  At  first  sight  it 
would  appear  probable  that  one  of  the  easiest  ways  to  diminish  the  blood- 
pressure  would  be  to  remove  blood  from  the  vessels  by  bleeding.  It  has 
been  found  by  experiment,  however,  that  although  the  blood-pressure 
sinks  whilst  large  abstractions  of  blood  are  taking  place,  as  soon  as  the 
bleeding  ceases  it  rises  rapidly,  and  speedily  becomes  normal ;  that  is  to 
say,  unless  so  large  an  amount  of  blood  has  been  taken  as  to  be  posi- 
tively dangerous  to  life,  abstraction  of  blood  has  little  effect  upon  the 
blood-pressure.  The  rapid  return  to  the  normal  pressure  is  due  not  so 
much  to  the  withdrawal  of  lymph  and  other  fluids  from  the  body  into  the 
blood,  as  was  formerly  supposed,  as  to  the  regulation  of  the  peripheral 
resistance  by  the  vaso-motor  nerves ;  in  other  words,  the  small  arteries 
contract,  and  in  so  doing  maintain  pressure  on  the  blood  and  favor  its  ac- 
cumulation in  the  arterial  system.  This  is  due  to  the  stimulation  of  the 
vaso-motor  centre  from  diminution  of  the  supply  of  blood,  and  therefore 
of  oxygen.  The  failure  of  the  blood-pressure  to  return  to  normal  in  the 
too  great  abstraction  must  be  taken  to  indicate  a  condition  of  exhaustion 
of  the  centre,  and  consequently  of  want  of  regulation  of  the  peripheral 
resistance.  In  the  same  way  it  might  be  thought  that  injection  of  blood 
into  the  already  pretty  full  vessels  would  be  at  once  followed  by  rise  in 
the  blood-pressure,  and  this  is  indeed  the  case  up  to  a  certain  point — the 
pressure  does  rise,  but  there  is  a  limit  to  the  rise.  Until  the  amount  of 
blood  injected  equals  about  2  to  3  per  cent  of  the  body  weight,  the  pres- 
sure continues  to  rise  gradually  ;  but  if  the  amount  exceed  this  propor- 
tion, the  rise  does  not  continue.  In  this  case  therefore,  as  in  the  oppo- 
site when  blood  is  abstracted,  the  vaso-motor  apparatus  must  counteract 
the  great  increase  of  pressure,  but  now  by  dilating  the  small  vessels,  and 
so  diminishing  the  peripheral  resistance,  for  after  each  rise  there  is  ^ 


THE    CIRCULATION    OF    THE    BLOOD.  153 

partial  fall  of  pressure  ;  and  after  the  limit  is  reached  the  whole  of  the 
injected  blood  displaces,  as  it  were,  an  equal  quantity  which  passes  into 
the  small  veins,  and  remains  within  them.  It  should  be  remembered 
that  the  veins  are  capable  of  holding  the  whole  of  the  blood  of  the  body. 

The  amount  of  blood  supplied  to  the  heart,  both  to  its  substance  and 
to  its  chambers,  has  a  marked 'effect  upon  the  blood-pressure. 

b.  As  regards  quality.  The  quality  of  the  blood  supplied  to  the  heart 
has  a  distinct  effect  upon  its  contraction,  as  too  watery  or  too  little  oxy- 
genated blood  must  interfere  with  its  action.  Thus  it  appears  that 
blood  containing  certain  substances  affects  the  peripheral  resistance  by 
acting  upon  the  muscular  fibres  of  the  arterioles  themselves  or  upon  the 
local  centres,  and  so  altering  directly,  as  it  were,  the  calibre  of  the  ves- 
sels. 

5.  Eespiratort/  changes  affecting  the  blood-pressure  will  be  considered 
in  the  next  Chapter. 

Circulation  in  the  Capillaries. 

When  the  capillary  circulation  is  examined  in  any  transparent  part 
of  a  full  grown  living  animal  by  means  of  the  microscope  (Fig.  139),  the 
blood  is  seen  to  flow  with  a  constant  equable  motion  ;  the  red  blood-cor- 
puscles moving  along,  mostly  in  single 
file,  and  bending  in  various  ways  to  ac- 
commodate themselves  to  the  tortuous 
course  of  the  capillary,  but  instantly  re- 
covering their  normal  outline  on  reach- 
ing a  wider  vessel. 

It  is  in  the  capillaries  that  the  chief 
resistance  is  offered  to  the  progress  of 
the  blood  ;  for  in  them  the  friction  of 
the  blood  is  greatly  increased  by  the  FlG  m -capillaries  coin  the  web 
enormous  multiplication  of  the  surface  2^  Sf^g0!  SiTSSff  v  <SS 
with  which  it  is  brought  in  contact.  Alien  Thomson). 

At  the  circumference  of  the  stream  in  the  larger  capillaries,  but  chiefly 
in  the  small  arteries  and  veins,  in  contact  with  the  walls  of  the  vessel, 
and  adhering  to  them,  there  is  a  layer  of  liquor  sanguinis  which  appears 
to  be  motionless.  The  existence  of  this  still  layer,  as  it  is  termed,  is  in- 
ferred both  from  the  general  fact  that  such  a  one  exists  in  all  fine  tubes 
traversed  by  fluid,  and  from  what  can  be  seen  in  watching  the  move- 
ments of  the  blood-corpuscles.  The  red  corpuscles  occupy  the  middle 
of  the  stream,  and  move  with  comparative  rapidity  ;  the  colorless  lymph- 
corpuscles  run  much  more  slowly  by  the  walls  of  the  vessel  ;  while  next 
to  the  wall  there  is  often  a  transparent  space  in  which  the  fluid  appears 
to  be  at  rest ;  for  if  any  of  the  corpuscles  happen  to  be  forced  within  it, 


154 


HANDBOOK    OF    PHYSIOLOGY, 


they  move  more  slowly  than  before,  rolling  lazily  along  the  side  of  the 
vessel,  and  often  adhering  to  its  wall.  Part  of  this  slow  movement  of 
the  pale  corpuscles  and  their  occasional  stoppage  may  be  due  to  their 
having  a  natural  tendency  to  adhere  to  the  walls  of  the  vessels.  Some- 
times, indeed,  when  the  motion  of  the  blood  is  not  strong,  many  of  the 
white  corpuscles  collect  in  a  capillary  vessel,  and  for  a  time  entirely  pre- 
vent the  passage  of  the  red  corpuscles. 

Intermittent  flow  in  the  Capillaries. — When  the  peripheral  re- 
sistance is  greatly  diminished  by  the  dilatation  of  the  small  arteries  and 
capillaries,  so  much  blood  passes  on  from  the  arteries  into  the  capillaries 
at  each  stroke  of  the  heart,  that  there  is  not  sufficient  remaining  in  the 
arteries  to  distend  them.  Thus,  the  intermittent  current  of  the  ventric- 
ular systole  is  not  converted  into  a  continuous  stream  by  the  elasticity 
of  the  arteries  before  the  capillaries  are  reached;  and  so  intermittency 
of  the  flow  occurs  in  capillaries  and  veins  and  a  pulse  is  produced.  The 
same  phenomenon  may  occur  when  the  arteries  become  rigid  from  dis- 
ease, and  when  the  beat  of  the  heart  is  so  slow  or  so  feeble  that  the  blood 
at  each  cardiac  systole  has  time  to  pass  on  to  the  capillaries  before  the 
next  stroke  occurs;  the  amount  of  blood  sent  at  each  stroke  being  insuf- 
ficient to  properly  distend  the  elastic  arteries. 

Diapedesis  of  Blood-Corpuscles. — It  was  formerly  supposed  that 
the  occurrence  of  any  transudation  from  the 
interior  of  the  capillaries  into  the  midst  of  the 
surrounding  tissues  was  confined,  in  the  absence 
of  injury,  strictly  to  the  fluid  part  of  the  blood; 
in  other  words,  that  the  corpuscles  could  not 
escape  from  the  circulating  stream,  unless  the 
wall  of  the  containing  blood-vessel  was  rup- 
tured. It  is  true  that  an  English  physiologist, 
Augustus  Waller,  affirmed,  in  1846,  that  he 
had  seen  blood-corpuscles,  both  red  and  white, 
pass  bodily  through  the  wall  of  the  capillary 
vessel  in  which  they  were  contained  (thus  con- 
firming what  had  been  stated  a  short  time  pre- 
viously by  Addison);  and  that,  as  no  opening 
could  be  seen  before  their  escape,  so  none 
could  be  observed  afterwards — so  rapidly  was 
the  part  healed.  But  these  observations  did 
not  attract  much  notice  until  the  phenomena 
of  escape  of  the  blood-corpuscles  from  the  capil- 
laries and  minute  veins,  apart  from  mechanical 
injury,  were  re-discovered  by  Cohnheim  in  1867. 

Cohnheim's  experiment  demonstrating  the  passage  of  the  corpuscles 
through  the  wall  of  the  blood-vessel,  is  performed  in  the  following  man  - 


Fig.  140.— A  large  capillary 
from  the  frog  s  mesentery- 
eight  hours  after  irritation 
had  been  set  up,  showing  emi- 
gration of  leucocytes,  a,  Cells 
m  the  act  of  traversing  the 
capillary  wall;  b,  some  already 
escaped.    (Freyj 


THE    CIRCULATION    OF   THE    BLOOD.  155 

ner.  A  frog  is  urarized,  that  is  to  say,  paralysis  is  produced  by  injecting 
under  the  skin  a  minute  quantity  of  the  poison  called  urari ;  and  the 
abdomen  having  been  opened,  a  portion  of  small  intestine  is  drawn  out, 
and  its  transparent  mesentery  spread  out  under  a  microscope.  After  a 
variable  time,  occupied  by  dilatation,  following  contraction  of  the  minute 
vessels  and  accompanying  quickening  of  the  blood-stream,  there  ensues 
a  retardation  of  the  current,  and  blood-corpuscles,  both  red  and  white, 
begin  to  make  their  way  through  the  capillaries  and  small  veins. 

"  Simultaneously  with  the  retardation  of  the  blood-stream,  the  leu- 
cocytes, instead  of  loitering  here  and  there  at  the  edge  of  the  axial  cur- 
rent, begin  to  crowd  in  numbers  against  the  vascular  wall.  In  this  way 
the  vein  becomes  lined,  with  a  continuous  pavement  of  these  bodies, 
which  remain  almost  motionless,  notwithstanding  that  the  axial  current 
sweeps  by  them  as  continuously  as  before,  though  with  abated  velocity. 
Now  is  the  moment  at  which  the  eye  must  be  fixed  on  the  outer  contour 
of  the  vessel,  from  which,  here  and  there,  minute,  colorless,  button- 
shaped  elevations  spring,  just  as  if  they  were  produced,  by  budding  out 
of  the  wall  of  the  vessel  itself.  The  buds  increase  gradually  and  slowly 
in  size,  until  each  assumes  the  form  of  a  hemispherical  projection,  of 
width  corresponding  to  that  of  the  leucocyte.  Eventually  the  hemi- 
sphere is  converted  into  a  pear-shaped  body,  the  small  end  of  which  is 
still  attached  to  the  surface  of  the  vein,  while  the  round  part  projects 
freely.  Gradually  the  little  mass  of  protoplasm  removes  itself  farther 
and  farther  away,  and,  as  it  does  so,  begins  to  shoot  out  delicate  prongs 
of  transparent  protoplasm  from  its  surface,  in  nowise  differing  in  their 
aspect  from  the  slender  thread  by  which  it  is  still  moored  to  the  vessel. 
Finally  the  thread  is  severed  and  the  process  is  complete/'  (Burdon- 
Sanderson.) 

The  process  of  diapedesis  of  the  red  corpuscles,  which  occurs  under 
circumstances  of  impeded  venous  circulation,  and  consequently  increased 
blood-pressure,  resembles  closely  the  migration  of  the  leucocytes,  with 
the  exception  that  they  are  squeezed  through  the  wall  of  the  vessel,  and 
do  not,  like  them,  work  their  way  through  by  amoeboid  movement. 

Various  explanations  of  these  remarkable  phenomena  have  been  sug- 
gested. Some  believe  that  the  psendo-stomata  between  contiguous  endo- 
thelial cells  (p.  22)  provide  the  means  of  escape  for  the  blood-corpuscles. 
But  the  chief  share  in  the  process  is  to  be  found  in  the  vital  endowments 
with  respect  to  mobility  and  contraction  of  the  parts  concerned — both  of 
the  corpuscles  (Bastian)  and  the  capillary  wall  (Strieker).  Burdon-San- 
derson  remarks:  "  The  capillary  is  not  a  dead  conduit,  but  a  tube  of  living 
protoplasm.  There  is  no  difficulty  in  understanding  how  the  membrane 
may  open  to  allow  the  escape  of  leucocytes,  and  close  again  after  they 
have  passed  out;  for  it  is  one  of  the  most  striking  peculiarities  of  con- 
tractile substance  that  when  two  parts  of  the  same  mass  are  separated, 


156  HANDBOOK    OF   PHYSIOLOGY. 

and  again  brought  into  contact,  they  melt  together  as  if  they  had  not 
been  severed. " 

Hitherto,  the  escape  of  the  corpuscles  from  the  interior  of  the  blood- 
vessels into  the  surrounding  tissues  has  been  studied  chiefly  in  connection 
with  pathology.  But  it  is  impossible  to  say,  at  present,  to  what  degree 
the  discovery  may  not  influence  all  present  notions  regarding  the  nutri- 
tion of  the  tissues,  oven  in  health. 

Vital  Capillary  Force. — The  circulation  through  the  capillaries  must, 
of  necessity,  be  largely  influenced  by  that  which  occurs  in  the  vessels  on 
either  side  of  them — in  the  arteries  or  the  veins;  their  intermediate  posi- 
tion causing  them  to  feel  at  once,  so  to  speak,  any  alteration  in  the  size 
or  rate  of  the  arterial  or  venous  blood-stream.  Thus,  the  apparent  con- 
traction of  the  capillaries,  on  the  application  of  certain  irritating  sub- 
stances, and  during  fear,  and  their  dilatation  in  blushing,  may  be  referred 
to  the  action  of  the  small  arteries,  rather  than  to  that  of  the  capillaries 
themselves.  But  largely  as  the  capillaries  are  influenced  by  these,  and 
by  the  conditions  of  the  parts  which  surround  and  support  them,  their 
own  endowments  must  not  be  disregarded.  They  must  be  looked  upon, 
not  as  mere  passive  channels  for  the  passage  of  blood,  but  as  possessing 
endowments  of  their  own  (vital  capillary  force),  in  relation  to  the  circu- 
lation. The  capillary  wall  is  actively  living  and  contractile,  and  there  is 
no  reason  to  doubt  that,  as  such,  it  must  have  an  important  influence  in 
connection  with  the  blood-current. 

Blood-Pressure  in  the  Capillaries — From  observations  upon  the 
web  of  the  frog's  foot,  the  tongue  and  mesentery  of  the  frog,  the  tails  of 
newts  and  small  fishes  (Roy  and  Brown),  as  well  as  upon  the  skin  of  the 
finger  behind  the  nail  (Kries),  by  careful  estimation  of  the  amount  of 
pressure  required  to  empty  the  vessels  of  blood  under  various  conditions, 
it  appears  that  the  blood-pressure  is  subject  to  variations  in  the  capilla- 
ries, apparently  following  the  variations  of  that  of  the  arteries;  and  that 
up  to  a  certain  point,  as  the  extravascular  pressure  is  increased,  so  does 
the  pulse  in  the  arterioles,  capillaries,  and  venules  become  more  and 
more  evident.  The  pressure  in  the  first  case  (web  of  the  frog's  foot) 
has  been  found  to  be  equal  to  about  14  to  20  mm.  of  mercury  ;  in 
other  experiments  to  be  equal  to  about  \  to  £  of  the  ordinary  arterial 
pressure. 

The  Circulation  in  the  Veins. 

The  blood-current  in  the  veins  is  maintained  by  the  slight  vis  a  tergo 
remaining  of  the  contraction  of  the  left  ventricle.  Very  effectual  as- 
sistance, moreover,  to  the  flow  of  blood  is  afforded  by  the  action  of  the 
muscles  capable  of  pressing  on  such  veins  as  have  valves,  as  well  as  by 
the  suction  action  of  the  heart. 

The  effect  of  such  muscular  pressure  may  be  thus  explained.     AVhen 


THE   CIKCULATION    OF    THE    BLOOD.  157 

pressure  is  applied  to  an)'  part  of  a  vein,  and  the  current  of  blood  in  it 
is  obstructed,  the  portion  behind  the  seat  of  pressure  becomes  swollen 
and  distended  as  far  back  as  to  the  next  pair  of  valves.  These,  acting 
like  the  semilunar  valves  of  the  heart,  and  being,  like  them,  inextensible 
both  in  themselves  and  at  their  margins  of  attachment,  do  not  follow  the 
vein  in  its  distention,  but  are  drawn  out  towards  the  axis  of  the  canal. 
Then,  if  the  pressure  continues  on  the  vein,  the  compressed  blood,  tend- 
ing to  move  equally  in  all  directions,  presses  the  valves  down  into  con- 
tact at  their  free  edges,  and  they  close  the  vein  and  prevent  regurgitation 
of  the  blood.  Thus,  whatever  force  is  exercised  by  the  pressure  of  the 
muscles  on  the  veins;  is  distributed  partly  in  pressing  the  blood  onwards 
in  the  proper  course  of  the  circulation,  and  partly  in  pressing  it  back- 
wards and  closing  the  valves  behind  (Fig.  109,  A  and  B). 

The  circulation  might  lose  as  much  as  it  gains  by  such  compression 
of  the  veins,  if  it  were  not  for  the  numerous  anastomoses  by  which  they 
communicate,  one  with  another;  for  through  these,  the  closing  up  of  the 
venous  channel  by  the  backward  pressure  is  prevented  from  being  any 
serious  hindrance  to  the  circulation,  since  the  blood,  of  which  the  onward 
course  is  arrested  by  the  closed  valves,  can  at  once  pass  through  some 
anastomosing  channel,  and  proceed  on  its  way  by  another  vein.  Thus, 
therefore,  the  effect  of  muscular  pressure  upon  veins  which  have  valves, 
is  turned  almost  entirely  to  the  advantage  of  the  circulation;  the  pres- 
sure of  the  blood  onwards, is  all  advantageous,  and  the  pressure  of  the 
blood  backwards  is  prevented  from  being  a  hindrance  by  the  closure  of 
the  valves  and  the  anastomoses  of  the  veins. 

The  effects  of  such  muscular  pressure  are  well  shown  by  the  accelera- 
tion of  the  stream  of  blood,  when,  in  venesection,  the  muscles  of  the 
fore-arm  are  put  in  action,  and  by  the  general  acceleration  of  the  circu- 
lation during  active  exercise:  and  the  numerous  movements  which  are 
contiuually  taking  place  in  the  body  while  awake,  though  their  single 
effects  maybe  less  striking,  must  be  an  important  auxiliary  to  the  venous 
circulation.  Yet  they  are  not  essential;  for  the  venous  circulation  con- 
tinues unimpaired  in  parts  at  rest,  in  paralyzed  limbs,  and  in  parts  in 
which  the  veins  are  not  subject  to  any  muscular  pressure. 

Rhythmical  Contraction  of  Veins. — In  the  web  of  the  bat's  wing. 
the  veins  are  furnished  with  valves,  and  possess  the  remarkable  property 
of  rhythmical  contraction  and  dilatation,  whereby  the  current  of  blood 
within  them  is  distinctly  accelerated.  (Wharton  Jones.)  The  contrac- 
tion occurs,  on  an  average,  about  ten  times  in  a  minute;  the  existence  of 
valves  preventing  regurgitation,  the  entire  effect  of  the  contractions  was 
auxiliary  to  the  onward  current  of  blood.  Analogous  phenomena  have 
been  frequently  observed  in  other  animals. 

Blood-Pressure  in  the  Veins. — The  blood-pressure  gradually  les- 
sens as  we  proceed  from  arteries  near  the  heart  to  those  more  remote,  and 


158  HANDBOOK    OF   PHYSIOLOGY. 

again  from  these  to  the  capillaries,  and  thence  along  the  veins  to  the  right 
auricle.  The  blood-pressure  in  the  veins  is  nowhere  very  great,  but  is 
greatest  in  the  small  veins,  while  in  the  large  veins  towards  the  heart  the 
pressure  becomes  negative,  or,  in  other  words,  when  a  vein  is  put  in  con- 
nection with  a  mercurial  manometer,  the  mercury  will  fall  in  the  arm 
farthest  away  from  the  vein,  and  will  rise  in  the  arm  nearest  the  vein, 
which  has  a  tendency  to  suck  in  rather  than  to  push  forward.  In  the 
large  veins  of  the  neck  this  tendency  to  suck  in  air  is  especially  marked, 
and  is  the  cause  of  death  in  some  surgical  operations  in  that  region. 
The  amount  of  pressure  in  the  brachial  vein  is  said  to  support  9  mm.  of 
mercury,  whereas  the  pressure  in  the  veins  of  the  neck  is  about  equal  to 
a  negative  pressure  of  —3  to  —8  mm. 

The  variations  of  venous  pressure  during  systole  and  diastole  of  the 
heart  are  very  slight,  and  a  distinct  pulse  is  seldom  seen  in  veins  except 
under  very  extraordinary  circumstances. 

The  formidable  obstacle  to  the  upward  current  of  the  blood  in  the 
veins  of  the  trunk  and  extremities  in  the  erect  posture  supposed  to  be 
presented  by  the  gravitation  of  the  blood,  has  no  real  existence,  since 
the  pressure  exercised  by  the  column  of  blood  in  the  arteries,  will  be  al- 
ways sufficient  to  support  a  column  of  venous  blood  of  the  same  height 
as  itself:  the  two  columns  mutually  balancing  each  other.  Indeed,  so 
long  as  both  arteries  and  veins  contain  continuous  columns  of  blood,  the 
force  of  gravitation,  whatever  be  the  position  of  the  body,  can  have  no 
power  to  move  or  resist  the  motion  of  any  part  of  the  blood  in  any  direc- 
tion. The  lowest  blood-vessels  have,  of  course,  to  bear  the  greatest 
amount  of  pressure;  the  pressure  on  each  part  being  directly  propor- 
tionate to  the  height  of  the  column  of  blood  above  it:  hence  their  liability 
to  distention.  But  this  pressure  bears  equally  on  both  arteries  and 
veins,  and  cannot  either  move,  or  resist  the  motion  of,  the  fluid  they 
contain,  so  long  as  the  columns  of  fluid  are  of  equal  height  in  both,  and 
continuous. 

Velocity  of  the   Blood  Current. 

The  velocity  of  the  blood-current  at  any  given  point  in  the  various 
divisions  of  the  circulatory  system  is  inversely  proportional  to  their  sec- 
tional area  at  that  point.  If  the  sectional  area  of  all  the  branches  of  a 
vessel  united  were  always  the  same  as  that  of  the  vessel  from  which  they 
arise,  and  if  the  aggregate  sectional  area  of  the  capillary  vessels  were 
equal  to  that  of  the  aorta,  the  mean  rapidity  of  the  blood's  motion  in 
the  capillaries  would  be  the  same  as  in  the  aorta  and  largest  arteries;  and 
if  a  similar  correspondence  of  capacity  existed  in  the  veins  and  arteries, 
there  would  be  an  equal  correspondence  in  the  rapidity  of  the  circulation 
in  them.  But  the  arterial  and  venous  systems  maybe  represented  by  two 
truncated  cones  with  their  apices  directed  towards  the  heart;  the  area  of 


THE   CIRCULATION    OF  THE   BLOOD. 


159 


their  united  base  (the  sectional  area  of  the  capillaries)  being  400-800 
times  as  great  as  that  of  the  truncated  apex  representing  the  aorta. 
Thus  the  velocity  of  blood  in  the  capillaries  is  not  more  than  ji^  of  that 
in  the  aorta. 

(a.)  In  the  Arteries. — The  velocity  of  the  stream  of  blood  is  greater 
in  the  arteries  than  in  any  other  part  of  the  circulatory  system,  and  in 
them  it  is  greatest  in  the  neighborhood  of  the  heart,  d  during  the  ven- 
tricular systole.  The  rate  of  movement  dimin-  % 
ishes  during  the  diastole  of  the  ventricles,  and  in 
the  parts  of  the  arterial  system  most  distant  from 
the  heart.  Chauveau  has  estimated  the  rapidity  of 
the  blood-stream  in  the  carotid  of  the  horse  at  over 
20  inches  per  second  during  the  heart's  systole,  and 
nearly  6  inches  during  the  diastole  (520 — 150 
mm.) 

Estimation  of  the  Velocity. — Various  in- 
struments have  been  devised  for  measuring  the 
velocity  of  the  blood  stream  in  the  arteries.  Lud- 
wig's  "Stromuhr"  (Fig.  141)  consists  of  a  XJ- 
shaped  glass  tube  dilated  at  a  and  a',  the  ends  of 
which,  h  and  i,  are  of  known  calibre.  The  bulbs 
can  be  filled  by  a  common  opening  at  k.  The 
instrument  is  so  contrived  that  at  b  and  b',  the 
glass  part  is  firmly  fixed  into  metal  cylinders,  at- 
tached to  a  circular  horizontal  table,  c  c',  capable 
of  horizontal  movement  on  a  similar  table  d  d' 
about  the  vertical  axis  marked  in  figure  by  a  dotted 
line.  The  opening  in  c  c' ,  when  the  instrument 
is  in  position,  as  in  fig.,  corresponds  exactly  with  those  in  dd';  but  if  c  c'be 
turned  at  right  angles  to  its  present  position,  there  is  no  communication 
between  h  and  a,  and  i  and  a' ,  but  h  communicates  directly  with  i;  and 
if  turned  through  two  right  angles  c'  communicates  with  d,  and  c  with 
d' ,  and  there  is  no  direct  communication  between  h  and  *.  The  experi- 
ment is  performed  in  the  following  way: — The  artery  to  be  experimented 
upon  is  divided  and  connected  with  two  canulae  and  tubes  which  fit  it 
accurately  with  h  and  i — h  the  central  end,  and  %  the  peripheral;  the 
bulb  a  is  filled  with  olive  oil  up  to  a  point  rather  lower  than  k,  and  a' 
and  the  remainder  of  a  is  filled  with  defibrinated  blood;  the  tube  on  &is 
then  carefully  clamped;  the  tubes  d  and  d'  are  also  filled  with  defibrin- 
ated blood.  When  everything  is  ready,  the  blood  is  allowed  to  flow  into 
a  through  h,  and  it  pushes  before  it  the  oil,  and  that  the  defibrinated 
blood  into  the  artery  through  i,  and  replaces  it  in  a' ;  when  the  blood 
reaches  the  former  level  of  the  oil  in  a,  the  disc  c  c'  is  turned  rapidly 
through  two  right  angles,  and  the  blood  flowing  through  d  into  a'  again 
displaces  the  oil  which  is  driven  into  a.  This  is  repeated  several  times, 
and  the  duration  of  the  experiment  noted.  The  capacity  of  a  and  a'  is 
known;  the  diameter  of  the  artery  is  also  known  by  its  corresponding 
with  the  cauulai  of  known  diameter,  and  as  the  number  of  tunes  a  has 


Fig.  141.—  Ludwig'a 
Stromuhr. 


160 


HANDBOOK    OF    PHYSIOLOGY. 


been  filled  in  a  given  time  is  known,  the  velocity  of  the  current  can  be 
calculated. 

Chauveau's  instrument  (Fig.  142)  consists  of  a  thin  brass  tube,  a,  in 
one  side  of  which  is  a  small  perforation  closed  by  thin  vulcanized  india- 
rubber.     Passing  through  the  rubber  is  a  fine  lever,  one  end  of  which, 


Fig.  142. — Diagram  of  Chauveau's  Instrument,  a,  Brass  tube  for  the  introduction  into  tne 
lumen  of  the  artery,  and  containing  an  index-needle,  which  passes  through  the  elastic  membrane 
in  its  side,  and  moves  by  the  impulse  of  the  blood  current,  c,  Graduated  scale,  for  measuring  the 
extent  of  the  oscillations  of  the  needle. 

slightly  flattened,  extends  into  the  lumen  of  the  tube,  while  the  other 
moves  over  the  face  of  a  dial.  The  tube  is  inserted  into  the  interior  of 
an  artery,  and  ligatures  applied  to  fix  it,  so  that  the  movement  of  the 
blood  may,  in  flowing  through  the  tube,  be  indicated  by  the  movement 
of  the  outer  extremity  of  the  lever  on  the  face  of  the  dial. 

The  Hmmatocho  meter  of  Vierordt,  and  the  instrument  of  Lortet,  re- 
semble in  principle  that  of  Ohauveau.' 

(b.)  In  the  Capillaries. — The  observations  of  Hales,  E.  H.  Weber, 
and  Valentin  agree  very  closely  as  to  the  rate  of  the  blood-current  in 
the  capillaries  of  the  frog;  and  the  mean  of  their  estimates  gives  the 
velocity  of  the  systemic  capillary  circulation  at  about  one  inch  (25  mm.) 
per  minute.  The  velocity  in  the  capillaries  of  warm-blooded  animals  is 
greater.  In  the  dog  TV  to  Tfff  inch  (.5  to  .73  mm.)  a  second.  This  may 
seem  inconsistent  with  the  facts,  which. show  that  the  whole  circulation 
is  accomplished  in  about  half  a  minute.  But  the  whole  length  of  capil- 
lary vessels,  through  which  any  given  portion  of  blood  has  to  pass,  prob- 
ably does  not  exceed  from  ^Va  to  ^g-th  of  an  inch  (.5  mm.);  and 
therefore  the  time  required  for  each  quantity  of  blood  to  traverse  its  own 
appointed  portion  of  the  general  capillary  system  will  scarcely  amount  to 
a  second. 

(c. )  In  the  Veins. — The  velocity  of  the  blood  is  greater  in  the  veins 
than  in  the  capillaries,  but  less  than  in  the  arteries:  this  fact  depending 
upon  the  relative  capacities  of  the  arterial  and  venous  systems.  If  an 
accurate  estimate  of  the  proportionate  areas  of  arteries  and  the  veins 
corresponding  to  them  could  be  made,  we  might,  from  the  velocity  of  the 
arterial  current,  calculate  that  of  the  venous.     A  usual  estimate  is,  that 


THE   CIRCULATION    OF   THK    BLOOD.  161 

the  capacity  of  the  veins  is  about  twice  or  three  times  as  great  as  that  of 
the  arteries,  and  that  the  velocity  of  the  blood's  motion  is,  therefore, 
about  twice  or  three  times  as  great  in  the  arteries  as  in  the  veins.  8  inches 
(about  200  mm.)  a  second.  The  rate  at  which  the  blood  moves  in  the 
veins  gradually  increases  the  nearer  it  approaches  the  heart,  for  the  sec- 
tional area  of  the  venous  trunks,  compared  with  that  of  the  branches 
opening  into  them,  becomes  gradually  less  as  the  trunks  advance  towards 
the  heart. 

(d.)  Of  the  Circulation  as  a  whole. — It  would  appear  that  a  por- 
tion of  blood  can  traverse  the  entire  course  of  the  circulation,  in  the 
horse,  in  half  a  minute.  Of  course  it  would  require  longer  to  traverse 
the  vessels  of  the  most  distant  part  of  the  extremities  than  to  go  through 
those  of  the  neck:  but  taking  an  average  length  of  vessels  to  be  traversed, 
and  assuming,  as  we  may,  that  the  movement  of  blood  in  the  human  sub- 
ject is  not  slower  than  in  the  horse,  it  may  be  concluded  that  half  a  min- 
ute represents  the  average  rate. 

Satisfactory  data  for  these  estimates  are  afforded  by  the  results  of 
experiments  to  ascertain  the  rapidity  with  which  poisons  introduced  into 
the  blood  are  transmitted  from  one  part  of  the  vascular  system  to  another. 
The  time  required  for  the  passage  of  a  solution  of  potassium  ferrocyanide. 
mixed  with  the  blood,  from  one  jugular  vein  (through  the  right  side  of 
the  heart,  the  pulmonary  vessels,  the  left  cavities  of  the  heart,  and  the 
general  circulation)  to  the  jugular  vein  of  the  opposite  side  varies  from 
twenty  to  thirty  seconds.  The  same  substance  was  transmitted  from  the 
jugular  vein  to  the  great  saphena  in  twenty  seconds;  from  the  jugular 
vein  to  the  masseteric  artery,  it  occupied  between  fifteen  and  thirty 
seconds;  to  the  facial  artery,  in  one  experiment,  in  between  ten  and  fif- 
teen seconds;  in  another  experiment  in  between  twenty  and  twenty-five 
seconds;  in  its  transit  from  the  jugular  vein  to  the  metatarsal  artery,  it 
occupied  between  twenty  and  thirty  seconds,  and  in  one  instance  more 
than  forty  seconds.  The  result  was  nearly  the  same  whatever  was  the 
rate  of  the  heart's  action. 

In  all  these  experiments,  it  is  assumed  that  the  substance  injected 
moves  with  the  blood,  and  at  the  same  rate,  and  does  not  move  from  one 
part  of  the  organs  of  circulation  to  another  by  diffusing  itself  through 
the  blood  or  tissues  more  quickly  that  the  blood  moves.  The  assumption 
is  sufficiently  probable  to  be  considered  nearly  certain,  that  the  times 
above  mentioned,  as  occupied  in  the  passage  of  the  injected  substances, 
are  those  in  which  the  portion  of  blood,  into  which  each  was  injected,  was 
carried  from  one  part  to  another  of  the  vascular  system. 

Another  mode  of  estimating  the  general  velocity  of  the  circulating 
blood,  is  by  calculating  it  from  the  quantity  of  blood  supposed  to  be  con- 
tained in  the  body,  and  from  the  quantity  which  can  pass  through  the 
heart  in  each  of  its  actions.  But  the  conclusions  arrived  at  by  this 
11 


162 


HANDBOOK    OF    PHYSIOLOGY. 


method  are  less  satisfactory.  For  the  total  quantity  of  blood,  and  the 
capacity  of  the  cavities  of  the  heart,  have  as  yet  been  only  approximately 
ascertained.  Still  the  most  careful  of  the  estimates  thus  made  accord 
very  nearly  with  those  already  mentioned  ;  and  it  may  be  assumed  that 
the  blood  may  all  pass  through  the  heart  in  from  twenty-five  to  fifty 
seconds. 

Local  Peculiarities  of  the  Circulation. 

The  most  remarkable  peculiarities  attending  the  circulation  of  blood 
through  different  organs  are  observed  in  the  cases  of  the  brain,  the  erec- 
tile organs,  the  lungs,  the  liver,  and  the  kidneys. 

1.  In  the  Brain. — For  the  due  performance  of  its  functions,  the 
brain  requires  a  large  supply  of  blood.  This  object  is  effected  through 
the  number  and  size  of  its  arteries,  the  two  internal  carotids,  and  the 
two  vertebrals.  It  is  further  necessary  that  the  force  with  which  this 
blood  is  sent  to  the  brain  should  be  less,  or  at  least  should  be  subject  to 
less  variation  from  external  circumstances  than  it  is  in  other  parts,  and 
so  the  large  arteries  are  very  tortuous  and  anastomose  freely  in  the  circle 
of  Willis,  which  thus  insures  that  the  supply  of  blood  to  the  brain  is 
uniform,  though  it  may  by  an  accident  be  diminished,  or  in  some  way- 
changed,  through  one  or  more  of  the  principal  arteries.  The  transit  of 
the  large  arteries  through  bone,  especially  the  carotid  canal  of  the  tem- 
poral bone,  may  prevent  any  undue  distention;  and  uniformity  of  supply 
is  further  insured  by  the  arrangement  of  the  vessels  in  the  pia  mater,  in 
which,  previous  to  their  distribution  to  the  substance  of  the  brain,  the 
large  arteries  breakup  and  divide  into  innumerable  minute  branches 
ending  in  capillaries,  which,  after  frequent  communication  with  one  an- 
other, enter  the  brain,  and  carry  into  nearly  every  part  of  it  uniform 
and  equable  streams  of  blood.  The  arteries  are  also  enveloped  in  a  spe- 
cial lymphatic  sheath.  The  arrangement  of  the  veins  within  the  cranium 
is  also  peculiar.  The  large  venous  trunks  or  sinuses  are  formed  so  as  to 
be  scarcely  capable  of  change  of  size;  and  composed,  as  they  are,  of  the 
tough  tissue  of  the  dura  mater,  and,  in  some  instances,  bounded  on  one 
side  by  the  bony  cranium,  they  are  not  compressible  by  any  force  which 
the  fulness  of  the  arteries  might  exercise  through  the  substance  of  the 
brain;  nor  do  they  admit  of  distention  when  the  flow  of  venous  blood 
from  the  brain  is  obstructed. 

The  general  uniformity  in  the  supply  of  blood  to  the  brain,  which  is 
thus  secured,  is  well  adapted,  not  only  to  its  functions,  but  also  to  its 
condition  as  a  mass  of  nearly  incompressible  substance  placed  in  a  cavity 
with  unyielding  walls.  These  conditions  of  the  brain  and  skull  formerly 
appeared,  indeed,  enough  to  justify  the  opinion  that  the  quantity  of  blood 
in  the  brain  must  be  at  all  times  the  same.  But  it  was  found  that  in 
animals  bled  to  death,  without  any  aperture  being  made  inthe  cranium, 


THE    CIRCULATION    OF    THE    BLOOD.  163 

the  brain  became  pale  and  anaemic  like  other  parts.  And  in  death  from 
strangling  or  drowning,  there  was  congestion  of  the  cerebral  vessels; 
while  in  death  by  prussic  acid,  the  quantity  of  blood  in  the  cavity  of  the. 
cranium  was  determined  by  the  position  in  which  the  animal  was  placed 
after  death,  the  cerebral  vessels  being  congested  when  the  animal  was 
suspended  with  its  head  downwards,  and  comparatively  empty  when  the 
animal  was  kept  suspended  by  the  ears.  Thus,  it  was  concluded,  al- 
though the  total  volume  of  the  contents  of  the  cranium  is  probably 
nearly  always  the  same,  yet  the  quantity  of  blood  in  it  is  liable  to  varia- 
tion, its  increase  or  diminution  being  accompanied  by  a  simultaneous 
diminution  or  increase  in  the  quantity  of  the  cerebro-spinal  fluid,  which, 
by  readily  admitting  of  being  removed  from  one  part  of  the  brain  and 
spinal  cord  to  another,  and  of  being  rapidly  absorbed,  and  as  readily  ef- 
fused, would  serve  as  a  kind  of  supplemental  fluid  to  the  other  contents 
of  the  cranium,  to  keep  it  uniformly  filled  in  case  of  variations  in  their 
quantity  (Burrows).  And  there  can  be  no  doubt  that,  although  the  ar- 
rangements of  the  blood-vessels,  to  which  reference  has  been  made,  in- 
sure to  the  brain  an  amount  of  blood  which  is  tolerably  uniform,  yet, 
inasmuch  as  with  every  beat  of  the  heart  and  every  act  of  respiration, 
and  under  many  other  circumstances,  the  quantity  of  blood  in  the  cavity 
of  the  cranium  is  constantly  varying,  it  is  plain  that,  were  there  not 
provision  made  for  the  possible  displacement  of  some  of  the  contents  of 
the  unyielding  bony  case  in  which  the  brain  is  contained,  there  would  be 
often  alternations  of  excessive  pressure  with  insufficient  supply  of  blood. 
Hence  we  may  consider  that  the  cerebro-spinal  fluid  in  the  interior  of  the 
skull  not  only  subserves  the  mechanical  functions  of  fat  in  other  parts  as 
a  packing  material,  but  by  the  readiness  with  which  it  can  be  displaced 
into  the  spinal  canal,  provides  the  means  whereby  undue  pressure  and 
insufficient  supply  of  blood  are  equally  prevented. 

Chemical  Composition  of  Cerebrospinal  Fluid. — The  cerebro-spinal 
fluid  is  transparent,  colorless,  not  viscid,  with  a  saline  taste  and  alkaline 
reaction,  and  is  not  affected  by  heat  or  acids.  It  contains  981-984 
parts  water,  sodium  chloride,  traces  of  potassium  chloride,  of  sulphates, 
carbonates,  alkaline  and  earthy  phosphates,  minute  traces  of  urea, 
sugar,  sodium  lactate,  fatty  matter,  cholesterin,  and  albumen  (Flint). 

(2.)  In  Erectile  Structures. — The  instances  of  greatest  variation  in 
the  quantity  of  blood  contained,  at  different  times,  in  the  same  organs, 
are  found  in  certain  structures  which,  under  ordinary  circumstances,  are 
soft  and  flaccid,  but,  at  certain  times,  receivean  unusually  large  quantity 
of  blood,  become  distended  and  swollen  by  it,  and  pass  into  the  state 
which  has  been  termed  erection.  Such  structures  are  the  corpora  caver- 
nosa  and  corpus  spongiosum  of  the  penis  in  the  male,  and  the  clitoris  in 
the  female;  and,  to  a  less  degree,  the  nipple  of  the  mammary  gland  in 
both  sexes.     The  corpus  cavernosum  penis,  which  is  the  best  example  of 


164  HANDBOOK    OF    PHYSIOLOGY. 

an  erectile  structure,  has  an  external  fibrous  membrane  or  sheath,  and 
from  the  inner  surface  of  the  latter  are  prolonged  numerous  fine  lamellae 
which  divide  its  cavity  into  small  compartments  looking  like  cells  when 
they  are  inflated.  Within  these  is  situated  the  plexus  of  veins  upon 
which  the  peculiar  erectile  property  of  the  organ  mainly  depends.  It 
consists  of  short  veins  which  very  closely  interlace  and  anastomose  with 
each  other  in  all  directions,  and  admit  of  great  variation  of  size,  collaps- 
ing in  the  passive  state  of  the  organ,  but,  for  erection,  capable  of  an 
amount  of  dilatation  which  exceeds  beyond  comparison  that  of  the  ar- 
teries and  veins  which  convey  the  blood  to  and  from  them.  The  strong 
fibrous  tissue  lying  in  the  intervals  of  the  venous  plexuses,  and  the  ex- 
ternal fibrous  membrane  or  sheath  with  which  it  is  connected,  limit  the 
distention  of  the  vessels,  and,  during  the  state  of  erection,  give  to  the 
penis  its  condition  of  tension  and  firmness.  The  same  general  condition 
of  vessels  exists  in  the  corpus  spongiosum  urethra?,  but  around  the  ure- 
thra the  fibrous  tissue  is  much  weaker  than  around  the  body  of  the 
penis,  and  around  the  glans  there  is  none.  The  venous  blood  is  returned 
from  the  plexuses  by  comparatively  small  veins;  those  from  the  glans  and 
the  fore  part  of  the  urethra  empty  themselves  into  the  dorsal  veins  of  the 
penis;  those  from  the  cavernosum  pass  into  deeper  veins  which  issue 
from  the  corpora  cavernosa  at  the  crura  penis;  and  those  from  the  rest 
of  the  urethra  and  bulb  pass  more  directly  into  the  plexus  of  the  veins 
about  the  prostate.  For  all  these  veins  one  condition  is  the  same; 
namely,  that  they  are  liable  to  the  pressure  of  muscles  when  they  leave 
the  penis.  The  muscles  chiefly  concerned  in  this  action  are  the  erector 
penis  and  accelerator  u  rinse.  Erection  results  from  the  distention  of  the 
venous  plexuses  with  blood.  The  principal  exciting  cause  in  the  erection 
of  the  penis  is  nervous  irritation,  originating  in  the  part  itself,  or  derived 
from  the  brain  and  spinal  cord.  The  nervous  influence  is  communicated 
to  the  penis  by  the  pudic  nerves,  which  ramify  in  its  vascular  tissue: 
and  after  their  division  in  the  horse,  the  penis  is  no  longer  capable  of 
erection. 

This  influx  of  the  blood  is  the  first  condition  necessary  for  erection, 
and  through  it  alone  much  enlargement  and  turgescence  of  the  penis 
may  ensue.  But  the  erection  is  probably  not  complete,  nor  maintained 
for  any  time  except  when,  together  with  this  influx,  the  muscles  already 
mentioned  contract,  and  by  compressing  the  veins,,  stop  the  efflux  of 
blood,  or  prevent  it  from  being  as  great  as  the  influx. 

It  appears  to  be  only  the  most  perfect  kind  of  erection  that  needs  the 
help  of  muscles  to  compress  the  veins  ;  and  none  such  can  materially 
assist  the  erection  of  the  nipples,  or  that  amount  of  turgescence,  just 
falling  short  of  erection,  of  which  the  spleen  and  many  other  parts  are 
capable.     For  such  turgescence  nothing  more  seems  necessary  than  a 


THK    CIKCULATIOX    OF    TIE    BLOOD.  165 

large  plexiform  arrangement  of  the  veins,  and  such  arteries  as  may  ad- 
mit, upon  occasion,  augmented  quantities  of  blood. 

(3,  4,  5.)  The  circulation  in  the  Lungs,  Liver,  and  Kidneys  will  be 
described  under  their  respective  heads. 

Agents  concerned  in  the  circulation. 

Before  quitting  the  subject  of  the  circulation  it  will  be  as  well  to 
bring  together  in  a  tabular  form  the  various  agencies  concerned  in 
maintaining  the  circulation. 

1.  The  Systole  and  Diastole  of  the  Heart,  the  former  pumping  into 
the  aorta  and  so  into  the  arterial  system  a  certain  amount  of  blood,  and 
the  latter  to  some  extent  sucking  in  the  blood  from  the  veins. 

2.  The  elastic  and  muscular  coats  of  the  arteries,  which  servo  to  keep 
up  an  equable  and  continuous  stream. 

3.  The  so-called  vital  capillary  force. 

4.  The  pressure  of  the  muscles  on  veins  with  valves,  and  the  slight 
rhythmic  contraction  of  the  veins. 

5.  Aspiration  of  the  thorax  during  inspiration,  by  means  of  which 
the  blood  is  drawn  from  the  large  veins  into  the  thorax  (to  be  treated  of 
in  next  Chapter). 

Proofs  of  the  Circulation  of  the  Blood. 

The  following  are  the  main  arguments  by  which  Harvey  established 
the  fact  of  the  circulation: — 

1.  The  heart  in  half  an  hour  propels  more  blood  than  the  whole  mass 
of  blood  in  the  body. 

2.  The  great  force  and  jetting  manner  with  which  the  blood  spurts 
from  an  opened  artery,  such  as  the  carotid,  with  every  beat  of  the  heart. 

3.  If  true,  the  normal  course  of  the  circulation  explains  why  after 
death  the  arteries  are  commonly  found  empty  and  the  veins  full. 

4.  If  the  large  veins  near  the  heart  were  tied  in  a  fish  or  snake,  the 
heart  became  pale,  flaccid,  and  bloodless  ;  on  removing  the  ligature, 
the  blood  again  flowed  into  the  heart.  If  the  artery  were  tied,  the  heart 
became  distended;  the  distention  lasting  until  the  ligature  was  removed. 

5.  The  evidence  to  be  derived  from  a  ligature  round  a  limb.  If  it 
be  drawn  very  tight,  no  blood  can  enter  the  limb,  and  it  becomes  pale 
and  cold.  If  the  ligature  be  somewhat  relaxed,  blood  can  enter  but  can- 
not leave  the  limb ;  hence  it  becomes  swollen  and  congested.  If  the 
ligature  be  removed,  the  limb  soon  regains  its  natural  appearance. 

G.  The  existence  of  valves  in  the  veins  which  only  permit  the  blood 
to  flow  towards  the  heart. 

7.  The  general  constitutional  disturbance  resulting  from  the  intro- 
duction of  a  poison  at  a  single  point,  e.  g.,  snake  poison. 


166  HANDBOOK    OF    PHYSIOLOGY. 

To  these  may  now  be  added  many  further  proofs  which  have  accu- 
mulated since  the  time  of  Harvey,  e.  g.  : — 

Wounds  of  arteries  and  veins.  In  the  former  case  hemorrhage  may 
be  almost  stopped  by  pressure  between  the  heart  and  the  wound,  in  the 
latter  by  pressure  beyond  the  seat  of  injury. 

9.  The  direct  observation  of  the  passage  of  blood-corpuscles  from 
small  arteries  through  capillaries  into  veins  in  all  transparent  vascular 
parts,  as  the  mesentery,  tongue  or  web  of  the  frog,  the  tail  or  gills  of  a 
tadpole,  etc. 

10.  The  results  of  injecting  certain  substances  into  the  blood. 
Further,  it  is  obvious  that  the  mere  fact  of  the  existence  of  a  hollow 

muscular  organ  (the  heart)  with  valves  so  arranged  as  to  permit  the 
blood  to  pass  only  in  one  direction,  of  itself  suggests  the  course  of  the 
circulation.  The  only  part  of  the  circulation  which  Harvey  could  not 
follow  is  that  through  the  capillaries,  for  the  simple  reason  that  he  had 
no  lenses  sufficiently  powerful  to  enable  him  to  see  it.  Malpighi  (1661) 
and  Leeuwenhoek  (1668)  demonstrated  it  in  the  tail  of  the  tadpole  and 
lung  of  the  frog. 


CHAPTER   V. 

RESPIRATION. 

The  maintenance  of  animal  life  necessitates  the  continual  absorption 
of  oxygen  and  excretion  of  carbonic  acid  ;  the  blood  being,  in  all  ani- 
mals which  possess  a  well-developed  blood-vascular  system,  the  medium 
by  which  these  gases  are  carried.  By  the  biood,  oxygen  is  absorbed 
from  without  and  conveyed  to  all  parts  of  the  organism  ;  and,  by  the 
blood,  carbonic  acid,  which  comes  from  within,  is  carried  to  those  parts 
by  which  it  may  escape  from  the  body.  The  two  processes — absorption 
of  oxygen  and  excretion  of  carbonic  acid — are  complementary,  and  their 
sum  is  termed  the  process  of  Respiration. 

In  all  Vertebrata,  and  in  a  large  number  of  Invertebrata,  certain 
parts,  either  lungs  or  gills,  are  specially  constructed  for  bringing  the 
blood  into  proximity  with  the  aerating  medium  (atmospheric  air,  or 
water  containing  air  in  solution).  In  some  of  the  lower  Vertebrata 
(frogs  and  other  naked  Amphibia)  the  skin  is  important  as  a  respiratory 
organ,  and  is  capable  of  supplementing,  to  some  extent,  the  functions 
of  the  proper  breathing  apparatus  ;  but  in  all  the  higher  animals,  includ- 
ing man,  the  respiratory  capacity  of  the  skin  is  so  infinitesimal  that  it 
may  be  practically  disregarded. 

Essentially,  a  lung  or  gill  is  constructed  of  a  fine  transparent  mem- 
brane, one  surface  of  which  is  exposed  to  the  air  or  water,  as  the  case 
may  be,  while,  on  the  other,  is  a  network  of  blood-vessels — the  only 
separation  between  the  blood  and  aerating  medium  being  the  thin  wall 
of  the  blood-vessels,  and  the  fine  membrane  on  one  side  of  which  vessels 
are  distributed.  The  difference  between  the  simplest  and  the  most  com- 
plicated respiratory  membrane  is  one  of  degree  only. 

The  various  complexity  of  the  respiratory  membrane,  and  the  kind 
of  aerating  medium,  are  not,  however,  the  only  conditions  which  cause  a 
difference  in  the  respiratory  capacity  of  different  animals.  The  number 
and  size  of  the  red  blood-corpuscles,  the  mechanism  of  the  breathing  ap- 
paratus, the  presence  or  absence  of  a  pulmonary  heart,  physiologically 
distinct  from  the  systemic,  are,  all  of  them,  conditions  scarcely  second 
in  importance. 

In  the  heart  of  man  and  all  other  Mammalia,  the  right  side  from 
which  the  blood  is  propelled  into  and  through  the  lungs  may  be  termed 


168  HANDBOOK    OF    PHYSIOLOGY. 

the  "pulmonary "  heart;  while  the  left  side  is  "systemic"  in  function. 
In  many  of  the  lower  animals,  however,  no  such  distinction  can  be 
drawn.  Thus,  in  Fish  the  heart  propels  the  blood  to  the  respiratory  or- 
gans (gills);  but  there  is  no  contractile  sac  corresponding  to  the  left 
side  of  the  heart,  to  propel  the  blood  directly  into  the  systemic  vessels. 

It  may  be  well  to  state  here  that  the  lungs  are  only  the  medium  for 
the  exchange,  on  the  part  of  the  blood,  of  carbonic  acid  for  oxygen. 
They  are  not  the  seat,  in  any  special  manner,  of  those  combustion  pro- 
cesses of  which  the  production  of  carbonic  acid  is  the  final  result. 
These  occur  in  all  parts  of  the  body — more  in  one  part,  less  in  another: 
chiefly  in  the  substance  of  the  tissues. 

The  Respiratory  Passages  and  Tissues. 

The  object  of  respiration  being  the  interchange  of  gases  in  the  lungs, 
it  is  necessary  that  the  atmospheric  air  shall  pass  into  them  and  be  ex- 
pelled from  them.  The  lungs  are  contained  in  the  chest  or  thorax,  which 
is  a  closed  cavity  having  no  communication  with  the  outside,  except  by 
means  of  the  respiratory  passages.  The  air  enters  these  passages  through 
the  nostrils  or  through  the  mouth,  thence  it  passes  through  the  larynx 
into  the  trachea  or  windpipe,  which  about  the  middle  of  the  chest  di- 
vides into  two  tubes  or  bronchi,  one  to  each  (right  and  left)  lung. 

The  Larynx  is  the  upper  part  of  the  passage  which  leads  exclusively 
to  the  lung:  it  is  formed  by  the  thyroid,  cricoid,  and  arytenoid  cartilages 
(Fig.  144),  and  contains  the  vocal  cords,  by  the  vibration  of  which  the 
voice  is  chiefly  produced.  These  vocal  cords  are  ligamentous  bands  at- 
tached to  certain  cartilages  capable  of  movement  by  muscles.  By  their 
approximation  the  cords  can  entirely  close  the  entrance  into  the  larynx; 
but  under  ordinary  conditions,  the  entrance  of  the  larynx  is  formed  by 
a  more  or  less  triangular  chink  between  them,  called  the  rima  glottidis. 
Projecting  at  an  acute  angle  between  the  base  of  the  tongue  and  the 
larynx  to  which  it  is  attached,  is  a  leaf -shaped  cartilage,  with  its  larger 
extremity  free,  called  the  epiglottis  (Fig.  144,  e).  The  whole  of  the 
larynx  is  lined  by  mucous  membrane,  which,  however,  is  extremely  thin 
over  the  vocal  cords.  At  its  lower  extremity  the  larynx  joins  the 
trachea.1  With  the  exception  of  the  epiglottis  and  the  so-called  corni- 
cula  laryngis,  the  cartilages  of  the  larynx  are  of  the  hyaline  variety. 

Structure  of  the  Epiglottis. — The  supporting  cartilage  of  the  epi- 
glottis is  composed  of  yellow  elastic  cartilage,  inclosed  in  a  fibrous 
sheath  (perichondrium),  and  covered  on  both  sides  with  mucous  mem- 
brane. The  anterior  surface,  which  looks  towards  the  back  of  the 
tongue,  is  covered  with  mucous  membrane,  the  basis  of  which  is  fibrous 

1  A  detailed  account  of  the  structure  and  function  of  the  Larynx  will  be  found  in 
Chapter  XVI. 


RESPIRATION. 


169 


tissue,  elevated  towards  both  surfaces  in  the  form  of  rudimentary  papillae, 
and  covered  with  several  layers  of  squamous  epithelium.  In  it  ramify 
capillary  blood-vessels,  and  in  its  meshes  are  a  large  number  of  lymphatic 
channels.  Under  the  mucous  membrane,  in  the  less  dense  fibrous 
tissue  of  which  it  is  composed,  are  a  number  of  tubular  glands.  The 
posterior  or  laryngeal  surface  of  the  epiglottis  is  covered  by  a  mucous 
membrane,  similar  in  structure  to  that  on  the  other  surface,  but  its  epi- 
thelial coat  is  thinner,  the  number  of  strata  of  cells  are  less,  and  the 


Fig.  143. 


papillae  few  and  less  distinct.  The  fibrous  tissue  which  constitutes  the 
mucous  membrane  is  in  great  part  of  the  adenoid  variety,  and  is  here 
and  there  collected  into  distinct  masses  or  follicles.  The  glands  of  the 
posterior  surface  are  smaller  but  more  numerous  than  those  of  the  other 
surface.  In  many  places  the  glands  which  are  situated  nearest  to  the 
perichondrium  are  directly  continuous  through  apertures  in  the  cartilage 
with  those  on  the  other  side,  and  often  the  ducts  of  the  glands  from  one 
side  of  the  cartilage  pass  through  and  open  upon  the  mucous  surface  of 
the  other  side.      Taste  goblets  have  been  found  in  the  epithelium  of  the 


170 


HANDBOOK    OF    PHYSIOLOGY. 


posterior  surface  of  the  epiglottis,  and  in  several  other  situations  in  the 
laryngeal  mucous  membrane. 

The  Trachea  and  Bronchial  Tubes.— The  trachea  or  wind-pipe 
extends  from  the  cricoid  cartilage,  which  is  on  a  level  with  the  fifth  cer- 


Fig.  144. 


Fig.  145. 


Fig.  144. — Outline  showing  the  general  form  of  the  larynx,  trachea,  and  bronchi,  as  seen  from 
before,  h,  the  great  cornu  of  the  hyoid  bone;  e,  epiglottis;  t,  superior,  and  V  inferior  cornu  of  the 
thyroid  cartilage ;  c,  middle  of  the  cricoid  cartilage ;  tr,  trachea,  showing  sixteen  cartilaginous  rings 
b,  the  right,  and  b  ,  the  left  bronchus.    CAUen  Thomson,  i    x  %. 

Fig.  145.— Outline  showing  the  general  form  of  the  larnyx,  trachea,  and  bronchi  as  seen  from 
behind,  h,  great  cornu  of  the  hyoid  bone,  t,  superior,  and  t',  the  inferior  cornu  of  the  thyroid 
cartilage;  e,  epiglottis;  a  points  to  the  back  of  both  the  arytenoid  cartilages,  which  are  surmounted 
by  the  cornicula;  e,  the  middle  ridge  on  the  back  of  the  cricoid  cartilage;  tr,  the  posterior  mem- 
branous part  of  the  trachea;  b,  b',  right  and  left  bronchi.    (Allen  Thomson.)    %. 


vical  vertebra,  to  a  point  opposite  the  third  dorsal  vertebra,  where  it 
divides  into  the  two  bronchi,  one  for  each  lung  (Fig.  144).  It  measures, 
on  an  average,  four  or  four  and  a  half  inches  in  length,  and  from  three- 
quarters  of  an  inch  to  an  inch  in  diameter. 


RESPIRATION. 


171 


Structure. — The  trachea  is  essentially  a  tube  of  fibro-elastic  mem- 
brane, within  the  layers  of  which  are  inclosed  a  series  of  cartilaginous 
rings,  from  sixteen  to  twenty  in  number.  These  rings  extend  only 
around  the  front  and  sides  of  the  trachea  (about  two-thirds  of  its  cir- 
cumference), and  are  deficient  behind;  the  interval  between  their  pos- 
terior extremities  being  bridged  over  by  a  continuation  of  the  fibrous 
membrane  in  which  they  are  inclosed  (Fig.  144).  The  cartilages  of  the 
trachea  aud  bronchial  tubes  are  of  the  hyaline  variety. 

Immediately  within  this  tube,  at  the  back,  is  a  layer  of  unstriped 


fc~ 


Fig.  146.— Section  of  the  trachea,  a,  columnar  ciliated  epithelium;  b  and  c,  proper  structure 
of  the  raucous  membrane,  containing  elastic  fibres  cut  across  transversely;  d,  submucous  tissue 
containing  mucous  glands,  e,  separated  from  the  hyaline  cartilage,  g.  by  a  fine  fibrous  tissue.  /:  h. 
external  investment  of  fine  fibrous  tissue.    tS.  K.  Alcock.) 


muscular  fibres,  which  extends,  transversely,  between  the  ends  of  the 
cartilaginous  rings  to  which  they  are  attached,  and  opposite  the  intervals 
between  them,  also;  their  evident  function  being  to  diminish,  when  re- 
quired, the  calibre  of  the  trachea  by  approximating  the  ends  of  the  car- 
tilages. Outside  theseare  a  few  longitudinal  bundles  of  muscular  tissue, 
which,  like  the  preceding,  are  attached  both  to  the  fibrous  and  cartila- 
ginous framework. 


1  i  '1  HANDBOOK    OF    PHYSIOLOGY. 

The  mucous  membrane  consists  of  adenoid  tissue,  separated  from  the 
stratified  columnar  epithelium  which  lines  it  by  a  homogeneous  base- 
ment membrane.  This  is  penetrated  here  and  there  by  channels  which 
connect  the  adenoid  tissue  of  the  mucosa  with  the  intercellular  substance 
of  the  epithelium.  The  stratified  columnar  epithelium  is  formed  of 
several  layers  of  cells  (Fig.  146),  of  which  the  most  superficial  layer  is 
ciliated,  and  is  often  branched  downwards  to  join  connective-tissue  cor- 
puscles, while  between  these  branched  cells  are  smaller  elongated  cells 
prolonged  up  towards  the  surface  and  down  to  the  basement  membrane. 
Beneath  these  are  one  or  more  layers  of  more  irregularly  shaped  cells. 
In  the  deeper  part  of  the  mucosa  are  many  elastic  fibres  between  which 
lie  connective-tissue  corpuscles  and  capillary  blood-vessels. 

Numerous  mucous  glands  are  situate  on  the  exterior  and  in  the  sub- 
stance of  the  fibrous  framework  of  the  trachea  ;  their  ducts  perforating 


Fig.  147.— Transverse  section  of  a  bronchus,  about  Y.  inch  in  diameter,  e,  Epithelium  (ciliated^; 
immediately  beneath  il  is  the  mucous  membrane  or  internal  fibrous  layer,  of  varying  thickness;  m, 
muscular  layer;  s,  m,  submucous  tissue;  /,  fibrous  tissue;  c,  cartilage  inclosed  within  the  layers  of 
fibrous  tissue;  g,  mucous  gland.    (F.  E.  Schultze.) 


the  various  structures  which  form  the  wall  of  the  trachea,  and  opening 
through  the  mucous  membrane  into  the  interior. 

The  two  bronchi  into  which  the  trachea  divides,  of  which  the  right 
is  shorter,  broader,  and  more  horizontal  than  the  left  (Fig.  144),  resem- 
ble the  trachea  exactly  in  structure,  and  in  the  arrangement  of  their  car- 
tilaginous rings.  On  entering  the  substance  of  the  lungs,  however,  the 
rings,  although  the\r  still  form  only  larger  or  smaller  segments  of  a 
circle,  are  no  longer  confined  to  the  front  and  sides  of  the  tubes,  butare 
distributed  impartially  to  all  parts  of  their  circumference. 

The  bronchi  divide  and  subdivide,  in  the  substance  of  the  lungs,  into 
a  number  of  smaller  and  smaller  branches,  which  penetrate  into  every 
part  of  the  organ,  until  at  length  they  end  in  the  smaller  subdivisions 
of  the  lungs,  called  lobules. 

All  the  larger  branches  still  have  walls  formed  of  tough  membrane, 
containing  portions  of  cartilaginous  rings,  by  which  they  are  held  open, 


KESPIRATION. 


173 


and  unstriped  muscular  fibres,  as  well  as  lougitudimil  bundles  of  elastic 
tissue.  They  are  lined  by  mucous  membrane,  the  surface  of  which,  like 
that  of  the  larynx  and  trachea,  is  covered  with  ciliated  epithelium  (Fig. 
146).  The  mucous  membrane  is  abundantly  provided  with  mucous 
glands. 

As  the  bronchi  become  smaller  and  smaller,  and  their  walls  thinner, 
the  cartilaginous  rings  become  scarcer  and  more  irregular,  until,  in  the 
smaller  bronchial  tubes,  they  are  represented  only  by  minute  and  scat- 
tered cartilaginous  flakes.  And  when  the  bronchi,  by  successive  branches 
are  reduced  to  about  ^  of  an  inch  in  diameter,  they  lose  their  cartilagi- 
nous element  altogether,  and  their  walls  are  formed  only  of  a  tough 
fibrous  elastic  membrane  with  circular  muscular  fibres  ;  they  are  still  lined, 
however,  by  a  thin  mucous  membrane,  with  ciliated  epithelium,  the 
length  of  the  cells  bearing  the  cilia  having  become  so  far  diminished 
that  the  cells  are  now  almost  cubical.     In  the  smaller  bronchi  the  circu- 


Fig.  148.— Transverse  section  of  the  chest. 

lar  muscular  fibres  are  more  abundant  than  in  the  trachea  and  larger 
bronchi,  and  form  a  distinct  circular  coat. 

The  Lungs  and  Pleurae. — The  Lungs  occupy  the  greater  portion 
of  the  thorax.  They  are  of  a  spongy  elastic  texture,  and  on  section  ap- 
pear to  the  naked  eye  as  if  they  were  in  great  part  solid  organs,  except 
here  and  there,  at  certain  points,  where  branches  of  the  bronchi  or  air- 
tubes  may  have  been  cut  across,  and  show,  on  the  surface  of  the  section, 
their  tubular  structure.  In  fact,  however,  the  lungs  are  hollow  organs, 
each  of  which  communicates  by  a  separate  orifice  with  a  common  air- 
tube,  the  trachea. 

The  Pleura. — Each  lung  is  enveloped  by  a  serous  membrane — the 
vleura,  one  layer  of  which  adheres  closely  to  the  surface,  and  provides  it 
with  its  smooth  and  slippery  covering,  while  the  other  adheres  to  the  in- 
ner surface  of  the  chest-wall.     The  continuitv  of  the  two  layers,  which 


174 


HANDBOOK    OF    PHYSIOLOGY. 


form  a  closed  sac,  as  in  the  case  of  other  serous  membranes,  will  be  best 
■understood  by  reference  to  Fig.  148.  The  appearance  of  a  space,  how- 
ever, between  the  pleura  which  covers  the  lung  {visceral  layer),  and  that 
which  lines  the  inner  surface  of  the  chest  {parietal  layer),  is  inserted  in 
the  drawing  only  for  the  sake  of  distinctness.  These  layers  are,  in 
health,  everywhere  in  contact,  one  with  the  other  ;  and  between  them  is 
only  just  so  much  fluid  as  will  insure  the  lungs  gliding  easily,  in  their 
expansion  and  contraction,  on  the  inner  surface  of  the  parietal  layer, 
which  lines  the  chest-wall.  While  considering  the  subject  of  normal 
respiration,  we  may  discard  altogether  the  notion  of  the  existence  of  any 
space  or  cavity  between  the  lungs  and  the  wall  of  the  chest. 

If,  however,  an  opening  be  made  so  as  to  permit  air  or  fluid  to  enter 
the  pleural  sac,  the  lung,  in  virtue  of  its  elasticity,  recoils,  and  a  con- 
siderable space  is  left  between  it  and  the  chest-wall.  In  other  words, 
the  natural  elasticity  of  the  lungs  would  cause  them  at  all  times  to  con- 


Fhj.  149.— Ciliary  epithelium  of  the  human  trachea,  a,  Layer  of  longitudinally  arranged  elastic 
fibres;  6,  basement  membrane;  <-,  deepest  cells,  circular  inform;  d,  intermediate  elongated  cells ; 
e,  outermost  layer  of  cells  fully  developed  and  bearing  cilia.     X  350.    (Kolliker.) 

tract  away  from  the  ribs,  were  it  not  that  t-he  contraction  is  resisted 
by  atmospheric  pressure  which  bears  only  on  the  inner  surface  of  the 
air-tubes  and  air-cells.  On  the  admission  of  air  into  the  pleural  sac,  at- 
mospheric pressure  bears  alike  on  the  inner  and  outer  surfaces  of  the 
lung,  and  their  elastic  recoil  is  thus  no  longer  prevented. 

Structure  of  the  Pleura  and  Lung. — The  pulmonary  pleura  consists 
of  an  outer  or  denser  layer  and  an  inner  looser  tissue.  The  former  or 
pleura  proper  consists  of  dense  fibrous  tissue  with  elastic  fibres,  covered 
by  endothelium,  the  cells  of  which  are  large,  flat,  hyaline,  and  transparent 
when  the  lung  is  expanded,  but  become  smaller,  thicker,  and  granular 
when  the  lung  collapses.  In  the  pleura  is  a  lymph-canalicular  system  ; 
and  connective-tissue  corpuscles  are  found  in  the  fibrous  tissue  which 
forms  its  groundwork.  The  inner,  looser,  or  subpleural  tissue  contains 
lamellae  of  fibrous  connective  tissue  and  connective-tissue  corpuscles  be- 
tween them.  Numerous  lymphatics  are  to  be  met  with,  which  form  a 
dense  plexus  of  vessels,  many  of  which  contain  valves.     They  are  simple 


KESPIRATION. 


175 


endothelial  tubes,  and  take  origin  in  the  lymph-canalicular  system  of  the 
pleura  proper.  Scattered  bundles  of  unstriped  muscular  fibre  occur  in 
the  pulmonary  pleura.  They  are  are  especially  strongly  developed  on 
the  anterior  and  internal  surfaces  of  the  lungs,  the  parts  which  move 
most  freely  in  respiration  :  their  function  is  doubtless  to  aid  in  expira- 
tion. The  structure  of  the  parietal  portion  of  the  pleura  is  very  similar 
to  that  of  the  visceral  layer. 

Each  lung  is  partially  subdivided  into  separate  portions  called  lobes; 
the  right  lung  into  three  lobes,  and  the  left  into  two.  Each  of  these 
lobes,  again,  is  composed  of  a  large  number  of  minute  parts,  called  Iod- 
ides. Each  pulmonary  lobule  may  be  considered  a  lung  in  miniature, 
consisting,  as  it  does,  of  a  branch  of  the  bronchial  tube,  of  air-cells, 
blood-vessels,  nerves,  and  lymphatics,  with  a  sparing  amount  of  areolar 

tissue. 

On   entering   a  lobule,  the   small  bronchial  tube,  the  structure  of 


Fig.  150. 


Fig.  151. 


Fig.  150.— Terminal  branch  of  a  bronchial  tube,  with  its  infundibula  and  air  cells,  from  the  mar- 
gin of  the  lung  of  a  monkey,  injected  with  quicksilver,  a,  terminal  bronchial  twig;  6  b,  infundib- 
ula and  air-cells,     x  10.    (F.'E.  Schulze.) 

Fig.  151.— Two  small  infundibula  or  groups  of  air-cells,  a  re,  with  air-cells,  6  6,  and  the  ultimate 
bronchial  tubes,  c  c,  with  which  the  aircellscommunicate.    From  a  new-born  child.    (Kolliker.) 

which  has  been  just  described  (a,  Fig.  151),  divides  and  subdivides ;  its 
walls  at  the  same  time  becoming  thinner  and  thinner,  until  at  length 
they  are  formed  only  of  a  thin  membrane  of  areolar  and  elastic  tissue, 
lined  by  a  layer  of  squamotis  epithelium,  not  provided  with  cilia.  At  the 
same  time,  they  are  altered  in  shape  ;  each  of  the  minute  terminal 
branches  widening  out  funnel-wise,  and  its  walls  being  pouched  out  ir- 
regularly into  small  saccular  dilatations,  called  air-cells  (Fig.  151,  b). 
Such  a  funnel-shaped  terminal  branch  of  the  bronchial  tube,  with  its 
group  of  pouches  or  air-cells,  has  been  called  an  infundibuhun  (Figs. 
150,  151),  and  the  irregular  oblong  space  in  its  centre,  with  which  the 
air-cells  communicate,  an  intercellular  passage. 


176 


HANDBOOK    OF  PHYSIOLOGY. 


The  air-cells,  or  air  vesicles,  may  be  placed  singly,  like  recesses  from 
the  intercellular  passage,  but  more  often  they  are  arranged  in  groups  or 
even  in  rows,  like  minute  sacculated  tubes  ;  so  that  a  short  series  of  ves- 
icles, all  communicating  with  one  another,  open  by  a  common  orifice 
into  the  tube.  The  vesicles  are  of  various  forms,  according  to  the  mu- 
tual pressure  to  which  they  are  subject ;  their  walls  are  nearly  in  contact, 
and  they  vary  from  -£w  to  TV  of  an  inch  in  diameter.  Their  walls  are 
formed  of  fine  membrane,  similar  to  that  of  the  intercellular  passages, 
and  continuous  with  it,  which  membrane  is  folded  on  itself  so  as  to  form 
a  sharp-edged  border  at  each  circular  orifice  of  communication  between 
contiguous  air-vesicles,  orbetween  the  vesicles  and  the  bronchial  pas- 


'  '   ^c 


■■■  ■ .■ ,- 


^5 

\ 


Fig.  152 —From  a  section  of  the  lung  of  a  cat,  stained  with  silver  nitrate.  A.  D.  Alveolar  duct 
or  intercellular  passage.  S.  Alveolar  septa.  N.  Alveoli  or  air-cells,  lined  with  large  flat,  nucleated 
cells,  with  some  smaller  polyhedral  nucleated  cells.  U.  Unstriped  muscular  fibres.  Circular  mus- 
cular fibres  are  seen  surrounding  the  interior  of  the  alveolar  duct,  and  at  one  part  is  seen  a  group 
of  small  polyhedral  cells  continued  from  the  bronchus.    (Klein  and  Noble  Smith.) 

sages.  Numerous  fibres  of  elastic  tissue  are  spread  out  between  contig- 
uous air-cells,  and  many  of  these  are  attached  to  the  outer  surface  of  the 
fine  membrane  of  which  each  cell  is  composed,  imparting  to  it  addi- 
tional strength,  and  the  power  of  recoil  after  distention.  The  cells  are 
lined  by  a  layer  of  epithelium  (Fig.  152),  not  provided  with  cilia.  Out- 
side the  cells,  a  network  of  pulmonary  capillaries  is  spread  out  so  dense- 
ly (Fig.  153),  that  the  interspaces  or  meshes  are  even  narrower  than  the 
vessels,  which  are,  on  an  average,  ^Vtt  °^  an  incn  m  diameter.  Between 
the  atmospheric  air  in  the  cells  and  the  blood  in  these  vessels,  nothing 
intervenes  but  the  thin  walls  of  the  cells  and  capillaries ;  and  the  ex- 


RESPIRATION. 


177 


posure  of  the  blood  to  the  air  is  the  more  complete,  because  the  folds 
of  membrane  between  contiguous  cells,  and  often  the  spaees  between 
tbe  walls  of  the  same,  contain  only  a  single  layer  of  capillaries,  both 
sides  of  which  are  thus  at  once  exposed  to  the  air. 

The  air-vesicles  situated  nearest  to  the  centre  of  the  lung  are  smaller 
and  their  networks  of  capillaries  are  closer  than  those  nearer  to  the  cir- 
cumference. The  vesicles  of  adjacent  lobules  do  not  communicate;  and 
those  of  the  same  lobule  or  proceeding  from  the  same  intercellular  pas- 
sage, do  so  as  a  general  rule  only  near  angles  of  bifurcation;  so  that, 
when  any  bronchial  tube  is  closed  or  obstructed,  the  supply  of  air  is  lost 
for  all  the  cells  opening  into  it  or  its  branches. 

Blood-supply. — The  lungs  receive  blood  from  two  sources,  (a)  the 
pulmonary  artery,  (b)  the  bronchial  arteries.  The  former  conveys  ven- 
ous blood  to  the  lungs  for  its  arterialization,  and  this  blood  takes  no 


Fig.  153.— Capillary  network  of  the  pulmonary  blood-vessels  in  the  human  lung, 
liker.) 


X  60.    (Kol- 


share  in  the  nutrition  of  the  pulmonary  tissues  through  •which  it  passes. 
(b)  The  branches  of  the  bronchial  arteries  ramify  for  nutrition's  sake  in 
the  walls  of  the  bronchi,  of  the  larger  pulmonary  vessels,  in  the  inter- 
lobular connective  tissue,  etc.  ;  the  blood  of  the  bronchial  vessels  being 
returned  chiefly  through  the  bronchial  and  partly  through  the  pulmo- 
nary veins. 

Lymphatics. — The  lymphatics  are  arranged  in  three  sets  : — 1.  Irreg- 
ular lacuna?  in  the  walls  of  the  alveoli  or  air-cells.  The  lymphatic  ves- 
sels which  lead  from  these  accompany  the  pulmonary  vessels  towards  the 
root  of  the  lung.  2.  Irregular  anastomosing  spaces  in  the  walls  of  the 
bronchi.  3.  Lymph-spaces  in  the  pulmonary  pleura.  The  lymphatic 
vessels  from  all  these  irregular  sinuses  pass  in  towards  the  root  of  the 
lung  to  reach  the  bronchial  glands. 
VI 


178 


HANDBOOK   OF    PHYSIOLOGY. 


Nerves. — The  nerves  of  the  lung  are  to  be  traced  from  the  anterior 
and  posterior  pulmonary  plexuses,  which  are  formed  by  branches  of  the 
vagus  and  sympathetic.  The  nerves  follow  the  course  of  the  vessels  and 
bronchi,  and  in  the  walls  of  the  latter  many  small  ganglia  are  situated. 

Mechanism  of  Respiration. 

Respiration  consists  of  the  alternate  expansion  and  contraction  of 
the  thorax,  by  means  of  which  air  is  drawn  into  or  expelled  from  the 
lungs.  These  acts  are  called  Inspiration  and  Expiration  respectively. 

For  the  inspiration  of  air  into  the  lungs  it  is  evident  that  all  that  is 
necessary  is  such  a  movement  of  the  side-walls  or  floor  of  the  chest,  or 
of  both,  that  the  capacity  of  the  interior  shall  be  enlarged.  By  such  in- 
crease of  capacity  there  will  be  of  course  a  diminution  of  the  pressure  of 


Fig.  154. — Diagram  of  axes  of  movement  of  ribs. 

the  air  in  the  lungs,  and  a  fresh  quantity  will  enter  through  the  larynx 
and  trachea  to  equalize  the  pressure  on  the  inside  and  outside  of  the 
chest. 

For  the  expiration  of  air,  on  the  other  hand,  it  is  also  evident  that, 
by  an  opposite  movement  which  shall  diminish  the  capacity  of  the  chest, 
the  pressure  in  the  interior  will  be  increased,  and  air  will  be  expelled, 
until  the  pressure  within  and  without  the  chest  are  again  eqiial.  In 
both  cases  the  air  passes  through  the  trachea  and  larynx,  whether  in  en- 
tering or  leaving  the  lungs,  there  being  no  other  communication  with 
the  exterior  of  the  body  ;  and  the  lung,  for  the  same  reason,  remains 
under  all  the  circumstances  described  closely  in  contact  with  the  walls 
and  floor  of  the  chest.  To  speak  of  expansion  of  the  chest,  is  to  speak 
also  of  expansion  of  the  lung. 


RESPIRATION. 


IT. i 


We  have  now  to  consider  the  means  by  which  the  respiratory  move- 
ments are  effected. 

Respiratory  Movements. 

A.  Inspiration. — The  enlargement  of  the  chest  in  inspiration  is  a 
muscular  act;  the  effect  of  the  action  of  the  inspiratory  muscles  being 
an  increase  in  the  size  of  the  chest-cavity  (a)  in  the  vertical,  and  (b)  in 
the  lateral  and  antero-posterior  diameters.  The  muscles  engaged  in 
ordinary  inspiration  are  the  diaphragm;  the  external  intercostals;  parts 
of  the  internal  intercostals;  the  levatores  costarum;  and  serratns  posti- 
cus superior. 

(a.)  The  vertical  diameter  of  the  chest  is  increased  by  the  contraction 
and  consequent  descent  of  the  diaphragm, — the  sides  of  the  muscle 
descending  most,  and  the  central  tendon  remaining  comparatively  un- 
moved; while  the  intercostal  and  other  muscles,  by  acting  at  the  same 


Fig.  155.— Diagram  of  movement  of  a  rib  in  inspiration. 

time,  prevent  the  diaphragm,  during  its  contraction,  from  drawing  in 
the  sides  of  the  chest. 

(b.)  The  increase  in  the  lateral  and  antero-posterior  diameters  of  the 
chest  is  effected  by  the  raising  of  the  ribs,  the  greater  number  of  which 
are  attached  very  obliquely  to  the  spine  and  sternum  (see  Figure  of 
Skeleton  in  frontispiece). 

The  elevation  of  the  ribs  takes  place  both  in  front  and  at  the  sides — 
the  hinder  ends  being  prevented  from  performing  any  upward  movement 
by  their  attachment  to  the  spine.  The  movement  of  the  front  extremi- 
ties of  the  rihs  is  of  necessity  accompanied  by  an  upward  and  forward 
movement  of  the  sternum  to  which  they  are  attached,  the  movement 
being  greater  at  the  lower  end  than  at  the  upper  end  of  the  latter  bone. 

The  axes  of  rotation  in  these  movements  are  two:  one  corresponding 
with  a  line  drawn   through  the  two  articulations  which  the    rib  forms 


180 


HANDBOOK    OF   PHYSIOLOGY. 


with  the  spine  (a  o,  Fig.  154);  and  the  other,  with  a  line  drawn  from 
one  of  these  (head  of  rib)  to  the  sternum  (A  B,  Fig.  154  and  Fig.  155); 
the  motion  of  the  rib  around  the  latter  axis  being  somewhat  after  the 
fashion  of  raising  the  handle  of  a  bucket. 

The  elevation  of  the  ribs  is  accompanied  by  a  slight  opening  out  of 
the  angle  which  the  bony  part  forms  with  its  cartilage  (Fig.  158,  A); 
and  thus  an  additional  means  is  provided  for  increasing  the  anteroposte- 
rior diameter  of  the  chest. 

The  muscles  by  which  the  ribs  are  raised,  in  ordinary  quiet  inspira- 
tion, are  the  external  intercostals,  and  that  portion  of  the  internal  inter- 
costals  which  is  situate  between  the  costal  cartilages;  and  these  are 
assisted  by  the  levatores  costarum,  and  the  serratus  posticus  superior. 
The  action  of  the  levatores  and  the  serratus  is  very  simple.     Their  fibres, 


S 


A 


£     c/y 


/'■> 


22- 


22 


E 


JT'Nn. 


E 


Fig.  156. 


Fig.  15? 


Fig.  156.— Diagram  of  apparatus  showing  the  action  of  the  external  intercostal  muscles. 
Fig.  157.— Diagram  of  apparatus  showing  the  action  of  the  internal  intercostal  muscles. 

arising  from  the  spine  as  a  fixed  point,  pass  obliquely  downwards  and 
forwards  to  the  ribs,  and  necessarily  raise  the  latter  when  they  contract. 
The  action  of  the  intercostal  muscles  is  not  quite  so  simple,  inasmuch  as, 
passing  merely  from  rib  to  rib,  they  seem  at  first  sight  to  have  no  fixed 
point  towards  which  they  can  pull  the  bones  to  which  they  are  attached. 

A  very  simple  apparatus  will  make  their  action  plain.  Such  an 
apparatus  is  shown  in  Fig.  156.  A  B  is  an  upright  bar,  representing  the 
spine,  with  which  are  jointed  two  parallel  bars,  C  and  D,  which  repre- 
sent two  of  the  ribs,  and  are  connected  in  front  by  movable  joints  with 
another  upright,  representing  the  sternum. 

If  with  such  an  apparatus  elastic  bands  be  connected  in  imitation  of 
the  intercostal  muscles,  it  will  be  found  that  when  stretched  on  the  bars 
after  the  fashion  of  the  external  intercostal  fibres  (Fig.  156,  C  D),  i.  e., 
passing   downwards   and   forwards,  they  raise   them   (Fig.  156,  C  D'); 


RESPIRATION.  1S1 

while  on  the  other  hand,  if  placed  in  imitation  of  the  position  of  the 
internal  intercostals  (Fig.  157,  E  F),  i.  e.,  passing  downwards  and  back- 
wards, they  depress  them  (Fig.  157,  E'  F'). 

The  explanation  of  the  foregoing  facts  is  very  simple.  The  intercos- 
tal muscles,  in  contracting,  merely  do  that  which  all  other  contracting 
fibres  do,  viz.,  bring  nearer  together  the  points  to  which  they  are 
attached;  and  in  order  to  do  this,  the  external  intercostals  must  raise 
the  ribs,  the  points  C  and  D  (Fig.  156)  being  nearer  to  each  other  when 
the  parallel  bars  are  in  the  position  of  the  dotted  lines.  The  limit  of 
the  movement  in  the  apparatus  is  reached  when  the  elastic  band  extends 
at  right  angles  to  the  two  bars  which  it  connects — the  points  of  attach- 
ment C  and  D'  being  then  at  the  smallest  possible  distance  one  from 
the  other. 

The  internal  intercostals  (excepting  those  fibres  which  are  attached  to 
the  cartilages  of  the  ribs)  have  an  opposite  action  to  that  of  the  external. 
In  contracting  they  must  pull  down  the  ribs,  because  the  points  E  and 
F  (Fig.  157)  can  only  be  brought  nearer  one  to  another  (Fig.  157,  E'  F') 
by  such  an  alteration  in  their  position. 

On  account  of  the  oblique  position  of  the  cartilages  of  the  ribs  with 
reference  to  the  sternum,  the  action  of  the  inter-cartilaginous  fibres  of 
the  internal  intercostals  must,  of  course,  on  the  foregoing  principles, 
resemble  that  of  the  external  intercostals. 

In  tranquil  breathing,  the  expansive  movements  of  the  lower  part  of 
the  chest  are  greater  than  those  of  the  upper.  In  forced  inspiration,  on 
the  other  hand,  the  greatest  extent  of  movement  appears  to  be  in  the 
upper  antero-posterior  diameter. 

Muscles  of  Extraordinary  Inspiration. — In  extraordinary  or 
forced  inspiration,  as  in  violent  exercise,  or  in  cases  in  which  there  is  some 
interference  with  the  due  entrance  of  air  into  the  chest,  and  in  which, 
therefore,  strong  efforts  are  necessary,  other  muscles  than  those  just 
•enumerated,  are  pressed  into  the  service.  It  is  very  difficult  or  impossi- 
ble to  separate  by  a  hard  and  fast  line,  the  so-called  muscles  of  ordinary 
from  those  of  extraordinary  inspiration;  but  there  is  no  doubt  that  the 
following  are  but  little  used  as  respiratory  agents,  except  in  cases  in 
which  unusual  efforts  are  required — the  scaleni  muscles,  the  sternomas- 
toid,  the  serratus  magnus,  the  pectorales,  and  the  trapezius. 

Types  of  Respiration. — The  expansion  of  the  chest  in  inspiration 
presents  some  peculiarities  in  different  persons.  In  young  children,  it 
is  effected  chiefly  by  the  diaphragm,  which,  being  highly  arched  in  ex- 
piration, becomes  flatter  as  it  contracts,  and,  descending,  presses  on  the 
abdominal  viscera,  and  pushes  forward  the  front  walls  of  the  abdomen. 
The  movement  of  the  abdominal  wall  being  here  more  manifest  than  that 
of  any  other  part,  it  is  usual  to  call  this  the  abdominal  type  of  respira- 
tion. In  men,  together  with  the  descent  of  the  diaphragm,  and  the 
pushing  forward  of  the  front  wall  of  the  abdomen,  the  chest  and  the 
sternum  are  subject  to  a  wide  movement  in  inspiration  (inferior  costal 
type).     In  women,  the  movement  appears  less  extensive  in  the  lower,  and 


1S2 


HANDBOOK    OF    PHYSIOLOGY. 


more  so  in  the  upper,  part   of  the   chest  {superior  costal  type).     (See 
Figs.  158,  159.) 

B.  Expiration  — From  the  enlargement  produced  in  inspiration, 
the  chest  and  lungs  return  in  ordinary  tranquil  expiration,  by  their  elas- 
ticity; the  force  employed  by  the  inspiratory  muscles  in  distending  the 
chest  and  overcoming  the  elastic  resistance  of  the  lungs  and  chest-walls, 
being  returned  as  an  expiratory  effort  when  the  muscles  are  relaxed. 
This  elastic  recoil  of  the  chest  and  lungs  is  sufficient,  in'  ordinary  quiet 
breathing,  to  expel  air  from  the  lungs  in  the  intervals  of  inspiration, 
and  no  muscular  power  is  required.  In  all  voluntary  expiratory  efforts, 
however,  as  in  speaking,  singing,  blowing,  and  the  like,  and  in  many 
involuntary  actions  also,  as  sneezing,  coughing,  etc.,  something  more 
than  merely  passive  elastic  power  is  necessary,  and  the  proper  expiratory 


Fig.  158. 


Fig.  159. 


Fig.  158.— The  changes  of  the  thoracic  and  abdominal  walls  of  the  male  during  respiration. 
The  back  is  supposed  to  be  fixed,  in  order  to  throw  forward  the  respiratory  movement  as  much  as 
possible.  The  outer  black  continuous  line  in  front  represents  the  ordinary  breathing  movement: 
the  anterior  margin  of  it  being  the  boundary  of  inspiration,  the  posterior  margin  the  limit  of  expi- 
ration. The  line  is  thicker  over  the  abdomen,  since  the  ordinary  respiratory  movement  is  chiefly  ab- 
dominal: thin  over  the  chest,  for  there  is  less  movement  over  that  region.  The  dotted  line  indicates 
the  movement  on  deep  inspiration,  during  which  the  sternum  advances  while  the  abdomen  recedes. 

Fig.  159.— The  respiratory  movement  in  the  female.  The  lines  indicate  the  same  changes  as  in 
the  last  figure.  The  thickness  of  the  continuous  line  over  the  sternum  shows  the  larger  extent  of 
the  ordinary  breathing  movement  over  that  region  in  the  female  than  in  the  male.  (John  Hutchin- 
son.) 

The  posterior  continuous  line  represents  in  both  figures  the  limit  of  forced  expiration. 

muscles  are  brought  into  action.  By  far  the  chief  of  these  are  the  ab- 
dominal muscles,  which,  by  pressing  on  the  viscera  of  the  abdomen, 
push  up  the  floor  of  the  chest  formed  by  the  diaphragm,  and  by  thus 
making  pressure  on  the  lungs,  expel  air  from  them  through  the  trachea 
and  larynx.  All  muscles,  however,  which  depress  the  ribs,  must  act  also 
as  muscles  of  expiration,  and  therefore  we  must  conclude  that  the  abdom- 
inal muscles  are  assisted  in  their  action  by  the  greater  part  of  the  internal 


RESPIRATION .  183 

intercostals,  the  triangularis  sterni,  the  serratus  posticus  inferior,  and 
quadratics  lumborum.  When  by  the  efforts  of  the  expiratory  muscles, 
the  chest  has  been  squeezed  to  less  than  its  average  diameter,  it  again,  on 
relaxation  of  the  muscles,  returns  to  the  normal  dimensions  by  virtue  of 
its  elasticity.  The  construction  of  the  chest-walls,  therefore,  admirably 
adapts  them  for  recoiling  against  and  resisting  as  well  undue  contraction 
as  undue  dilatation. 

In  the  natural  condition  of  the  parts,  the  lungs  can  never  contract  to 
the  utmost,  but  are  always  more  or  less  "  on  the  stretch,"  being  kept 
closely  in  contact  with  the  inner  surface  of  the  walls  of  the  chest  by 
cohesion  as  well  as  by  atmospheric  pressure,  and  can  contract  away  from 
these  only  when,  by  some  means  or  other,  as  by  making  an  opening  into 
the  pleural  cavity,  or  by  the  effusion  of  fluid  there,  the  pressure  on  the 
exterior  and  interior  of  the  lungs  becomes  equal.  Thus,  under  ordinary 
circumstances,  the  degree  of  contraction  or  dilatation  of  the  lungs  is 
dependent  on  that  of  the  boundary  walls  of  the  chest,  the  outer  surface 
of  the  one  being  in  close  contact  with  the'  inner  surface  of  the  other,  and 
obliged  to  follow  it  in  all  its  movements. 

Respiratory  Rhythm. — The  acts  of  expansion  and  contraction  of 
the  chest,  take  up,  under  ordinary  circumstances,  a  nearly  equal  time. 
The  act  of  inspiring  air,  however,  especially  in  women  and  children,  is 
a  little  shorter  than  that  of  expelling  it,  and  there  is  commonly  a  very 
slight  pause  between  the  end  of  expiration  and  the  beginning  of  the 
next  inspiration.     The  respiratory  rhythm  may  be  thus  expressed: — 

Inspiration, 6 

Expiration, 7  or  8 

A  very  slight  pause. 

Respiratory  Sounds. — If  the  ear  be  placed  in  contact  with  the  wall 
of  the  chest,  or  be  separated  from  it  only  by  a  good  conductor  of  sound 
or  stethoscope,  a  faint  respiratory  murmur  is  heard  during  inspiration. 
This  sound  varies  somewhat  in  different  parts — being  loudest  or  coarsest 
in  the  neighborhood  of  the  trachea  and  large  bronchi  (tracheal  and 
bronchial  breathing),  and  fadiug  off  into  a  faint  sighing  as  the  ear  is 
placed  at  a  distance  from  these  (vesicular  breathing).  It  is  best  heard 
in  children,  and  in  them  a  faint  murmur  is  heard  in  expiration  also. 
The  cause  of  the  vesicular  murmur  has  received  various  explanations. 
Most  observers  hold  that  the  sound  is  produced  by  the  friction  of  the  air 
against  the  walls  of  the  alveoli  of  the  lungs  when  they  are  undergoing 
distention  (Laennec,  Skoda),  others  that  it  is  due  to  an  oscillation  of  the 
current  of  air  as  it  enters  the  alveoli  (Chauveau),  whilst  others  believe 
that  the  sound  is  produced  in  the  glottis,  but  that  it  is  modified  in  its 
passage  to  the  pulmonary  alveoli  (Beau,  Gee). 

Respiratory  Movements  of  the  Nostrils  and  of  the  Glottis. — 


184  HANDBOOK    OF    PHYSIOLOGY= 

During  the  action  of  the  muscles  which  directly  draw  air  into  the  chest, 
those  which  guard  the  opening  through  which  it  enters  are  not  passive. 
In  hurried  breathing  the  instinctive  dilation  of  the  nostrils  is  well  seen, 
although  under  ordinary  conditions  it  may  not  be  noticeable.  The  open- 
ing at  the  upper  part  of  the  larynx,  however,  or  rima  glottidis  (Fig. 
143),  is  dilated  at  each  inspiration,  for  the  more  ready  passage  of  air,  and 
becomes  smaller  at  each  expiration;  its  condition,  therefore,  correspond- 
ing during  respiration  with  that  of  the  walls  of  the  chest.  There  is  a 
further  likeness  between  the  two  acts  in  that,  under  ordinary  circum- 
stances, the  dilatation  of  the  rima  glottidis  is  a  muscular  act,  and  its 
contraction  chiefly  an  elastic  recoil;  although,  under  various  conditions, 
to  be  hereafter  mentioned,  there  may  be,  in  the  latter,  considerable  mus- 
cular power  exercised. 

Terms  used  to  express  Quantity  of  Air  breathed. — a.  Breathing 
or  tidal  air,  is  the  quantity  of  air  which  is  habitually  and  almost  uni- 
formly changed  in  each  act  of  breathing.  In  a  healthy  adult  man  it  is 
about  30  cubic  inches. 

•  b.  Complemental  air,  is  the  quantity  over  and  above  this  which  can 
be  drawn  into  the  lungs  in  the  deepest  inspiration;  its  amount  is  various, 
as  will  be  presently  shown. 

c.  Reserve  air. — After  ordinary  expiration,  such  as  that  which  expels 
the  breathing  or  tidal  air,  a  certain  quantity  of  air  remains  in  the  lungs, 
which  may  be  expelled  by  a  forcible  and  deeper  expiration.  This  is 
termed  reserve  air. 

d.  Residual  air  is  the  quantity  which  still  remains  in  the  lungs  after 
the  most  violent  expiratory  effort.  Its  amount  depends  in  great  measure 
on  the  absolute  size  of  the  chest,  but  may  be  estimated  at  about  100  cubic 
inches. 

The  total  quantity  of  air  which  passes  into  and  out  of  the  lungs  of 
an  adult,  at  rest,  in  24  hours,  is  about  686,000  cubic  inches.  This  quan- 
tity, however,  is  largely  increased  by  exertion;  the  average  amount  for 
a  hard-working  laborer  in  the  same  time  being  1,568,390  cubic  inches. 

e.  Respiratory  Capacity. — The  greatest  respiratory  capacity  of  the 
chest  is  indicated  by  the  quantity  of  air  which  a  person  can  expel  from 
his  lungs  by  a  forcible  expiration  after  the  deepest  inspiration  that  he  can 
make;  it  expresses  the  power  which  a  person  has  of  breathing  in  the 
emergencies  of  active  exercise,  violence,  and  disease.  The  average 
capacity  of  an  adult  (at  60°  F.  or  15.4°  0.)  is  about  225  cubic  inches. 

•  The  respiratory  capacity,  or  as  Hutchinson  called  it,  vital  capacity, 
is  usually  measured  by  a  modified  gasometer  {spirometer  of  Hutchinson), 
into  which  the  experimenter  breathes — making  the  most  prolonged  ex- 
piration possible  after  the  deepest  possible  inspiration.  The  quantity 
of  air  which  is  thus  expelled  from  the  lungs  is  indicated  by  the  height 
to  which  the  air  chamber  of  the  spirometer  rises;  and  by  means  of  a 


KESPIRATION.  185 

scale  placed  in  connection  with  this,  the  number  of  cubic  inches  is  read 
off. 

In  healthy  men,  the  respiratory  capacity  varies  chiefly  with  the  sta- 
ture, weight,  and  age. 

It  was  found  by  Hutchinson,  from  whom  most  of  our  information  on 
this  subject  is  derived,  that  at  a  temperature  of  60°  F.,  225  cubic  inches 
is  the  average  vital  or  respiratory  capacity  of  a  healthy  person,  five  feet 
seven  inches  in  height. 

Circumstances  affecting  the  amount  of  respiratory  capacity. — For 
every  inch  of  height  above  this  standard  the  capacity  is  increased,  on  an 
average,  by  eight  cubic  inches;  and  for  every  inch  below,  it  is  diminished 
by  the  same  amount. 

The  influence  of  iveight  on  the  capacity  of  respiration  is  less  manifest 
and  considerable  than  that  of  height :  and  it  is  difficult  to  arrive  at  any 
definite  conclusions  on  this  point,  because  the  natural  average  weight  of 
a  healthy  man  in  relation  to  stature  has  not  yet  been  determined.  As  a 
general  statement,  however,  it  may  be  said  that  the  capacity  of  respira- 
tion is  not  affected  by  weights  under  161  pounds,  or  Hi  stones  ;  but 
that,  above  this  point,  it  is  diminished  at  the  rate  of  one  cubic  inch  for 
every  additional  pound  up  to  196  pounds,  or  14  stones. 

By  aye,  the  capacity  appears  to  be  increased  from  about  the  fifteenth 
to  the  thirty-fifth  year,  at  the  rate  of  five  cubic  inches  per  year ;  from 
thirty-five  to  sixty-five  it  diminishes  at  the  rate  of  about  one  and  a  half 
cubic  inch  per  year ;  so  that  the  capacity  of  respiration  of  a  man  of  sixty 
years  old  would  be  about  30  cubic  inches  less  than  that  of  a  man  forty 
years  old,  of  the  same  height  and  weight.     (John  Hutchinson.) 

Number   of  Respirations,  and   Relation  to  the  Pulse. — The 

number  of  respirations  in  a  healthy  adult  person  usually  ranges  from 
fourteen  to  eighteen  per  minute.  It  is  greater  in  infancy  and  childhood. 
It  varies  also  much  according  to  different  circumstances,  such  as  exer- 
cise or  rest,  health  or  disease,  etc.  Variations  in  the  number  of  respira- 
fciona  correspond  ordinarily  with  similar  variations  in  the  pulsations  of 
the  heart.  In  health  the  proportion  is  about  1  to  4,  or  1  to  5,  and  when 
the  rapidity  of  the  heart's  action  is  increased,  that  of  the  chest  move- 
ment is  commonly  increased  also  ;  but  not  in  every  case  in  equal  propor- 
tion. It  happens  occasionally  in  disease,  especially  of  the  lungs  or 
air-passages,  that  the  number  of  respiratory  acts  increases  in  quickerpro- 
portion  than  the  beats  of  the  pulse  ;  and,  in  other  affections,  much  more 
commonly,  that  the  number  of  the  pulses  is  greater  in  proportion  than 
that  of  the  respirations. 

There  can  be  no  doubt  that  the  number  of  respirations  of  any  given 
animal  is  largely  affected  by  its  size.  Thus,  comparing  animals  of  the 
same  kind,  in  a  tiger  (lying  quietly)  the  number  of  respirations  was  20 
per  minute,  while  in  a  small  leopard  (lying  quietly)  the  number  was  30. 
In  a  small  monkey  40  per  minute  ;  in  a  large  baboon,  20. 

The  rapid,  panting  respiration  of  mice,  even  when  quite  still,  is  fa- 
miliar, and  contrasts  strongly  with  the  slow  breathing  of  a  large  animal 


180  HANDBOOK    OF    PHYSIOLOGY. 

such  as  the  elephant  (eight  or  nine  times  per  minute).  These  facts  may 
be  explained  as  follows  : — The  heat-producing  power  of  any  given  animal 
depends  largely  on  its  bulk,  while  its  loss  of  heat  depends  to  a  great  ex- 
tent upon  the  surface  area  of  its  body.  If  of  two  animals  of  similar 
shape,  one  be  ten  times  as  long  as  the  other,  the  area  of  the  large  animal 
(representing  its  loss  of  heat)  is  100  times  that  of  the  small  one,  while 
its  bulk  (representing  production  of  heat)  is  about  1000  times  as  great. 
Thus  in  order  to  balance  its  much  greater  relative  loss  of  heat,  the 
smaller  animal  must  have  all  its  vital  functions,  circulation,  respiration, 
etc.,  carried  on  much  more  rapidly. 

Force  of  Inspiratory  and  Expiratory  Muscles. — The  force  with 
which  the  inspiratory  muscles  are  capable  of  acting  is  greatest  in  indivi- 
duals of  the  height  of  from  five  feet  seven  inches  to  five  feet  eight  inches, 
and  will  elevate  a  column  of  three  inches  of  mercury.  Above  this  height, 
the  force  decreases  as  the  stature  increases  ;  so  that  the  average  of  men 
of  six  feet  can  elevate  only  about  two  and  a  half  inches  of  mercury. 
The  force  manifested  in  the  strongest  expiratory  acts  is,  on  the  average, 
one-third  greater  than  that  exercised  in  inspiration.  But  this  difference 
is  in  great  measure  due  to  the  power  exerted  by  the  elastic  reaction  of 
the  walls  of  the  chest ;  and  it  is  also  much  influenced  by  the  dispropor- 
tionate strength  which  the  expiratory  muscles  attain,  from  their  being 
called  into  use  for  other  purposes  than  that  of  simple  expiration.  The 
force  of  the  inspiratory  act  is,  therefore,  better  adapted  than  that  of  the 
expiratory  for  testing  the  muscular  strength  of  the  body.  (John  Hut- 
chinson. ) 

The  instrument  used  by  Hutchinson  to  gauge  the  inspiratory  and  ex- 
piratory power  was  a  mercurial  manometer,  to  which  was  attached  a  tube 
fitting  the  nostrils,  and  through  which  the  inspiratory  or  expiratory  ef- 
fort was  made.  The  following  table  represents  the  results  of  numerous 
experiments  : 


Power  of 

Power  of 

Inspiratory  Muscles. 

Expiratory  Muscles. 

1.5  in.     . 

.     Weak,     . 

.     2.0  in. 

2.0  " 

Ordinary,    . 

2.5  " 

2.5  "      . 

Strong,  . 

.     3.5  " 

3.5  " 

Very  strong, 

4.5  " 

4.5  "      . 

Eemarkable,  . 

.     5.8  " 

5.5  " 

Very  remarkable, 

7.0  " 

6.0  "      . 

Extraordinary, 

.     8.5  " 

7.0  " 

Very  extraordinar; 

Y,  10.0  " 

The  greater  part  of  the  force  exerted  in  deep  inspiration  is  employed 
in  overcoming  the  resistance  offered  by  the  elasticity  of  the  walls  of  the 
chest  and  of  the  lungs. 

The  amount  of  this  elastic  resistance  was  estimated  by  observing  the 
elevation  of  a  column  of  mercury  raised  by  the  return  of  air  forced,  after 
death,  into  the  lungs,  in  quantity  equal  to  the  known  capacity  of  res- 


RESPIRATION.  187 

piration  during  life  ;  and  Hutchinson  calculated,  according  to  the  well- 
known  hydrostatic  law  of  equality  of  pressures  (as  shown  in  the  Bramah 
press),  that  the  total  force  to  be  overcome  by  the  muscles  in  the  act  of 
inspiring  200  cubic  inches  of  air  is  more  than  450  lbs. 

The  elastic  force  overcome  in  ordinary  inspiration  is,  according  to 
the  same  authority,  equal  to  about  170  lbs. 

Douglas  Powell  has  shown  that  within  the  limits  of  ordinary  tranquil 
respiration,  the  elastic  resilience  of  the  walls  of  the  chest  favors  inspira- 
tion; and  that  it  is  only  in  deep  inspiration  that  the  ribs  and  rib-carti- 
lages offer  an  opposing  force  to  their  dilatation.  In  other  words,  the 
elastic  resilience  of  the  lungs,  at  the  end  of  an  act  of  ordinary  breathing, 
has  drawn  the  chest-walls  within  the  limits  of  their  normal  degree  of  ex- 
pansion. Under  all  circumstances,  of  course,  the  elastic  tissue  of  the 
lungs  opposes  inspiration,  and  favors  expiration. 

Functions  of  Muscular  Tissue  of  Lungs. — It  is  possible  that 
the  contractile  power  which  the  bronchial  tubes  and  air-vesicles  possess, 
by  means  of  their  muscular  fibres  may  (1)  assist  in  expiration  ;  but  it  is 
more  likely  that  its  chief  purpose  is  (2)  to  regulate  and  adapt,  in  some 
measure,  the  quantity  of  air  admitted  to  the  lungs,  and  to  each  jDart  of 
them,  according  to  the  supply  of  blood  ;  (3)  the  muscular  tissue  con- 
tracts upon  and  gradually  expels  collections  of  mucus,  which  may  have 
accumulated  within  the  tubes,  and  which  cannot  be  ejected  by  forced 
expiratory  efforts,  owing  to  collapse  or  other  morbid  conditions  of  the 
portion  of  lung  connected  with  the  obstructed  tubes  (Gairdner).  (4) 
Apart  from  any  of  the  before-mentioned  functions,  the  presence  of  mus- 
cular fibre  in  the  walls  of  a  hollow  viscus,  such  as  a  lung,  is  only  what 
might  be  expected  from  analogy  with  other  organs.  Subject  as  the 
lungs  are  to  such  great  variation  in  size  it  might  be  anticipated  that  the 
elastic  tissue,  which  enters  so  largely  into  their  composition,  would  be 
supplemented  by  the  presence  of  much  muscular  fibre  also. 

Respiratory  Changes  in  the  Air  and  in  the  Blood. 

A.  In  the  Air. 

Composition  of  the  Atmosphere. — The  atmosphere  we  breathe  has,  in 
every  situation  in  which  it  has  been  examined  in  its  natural  state,  a 
nearly  uniform  composition.  It  is  a  mixture  of  oxygen,  nitrogen,  car- 
bonic acid,  and  watery  vapor,  with,  commonly,  traces  of  other  gases,  as 
ammonia,  sulphuretted  hydrogen,  etc.  Of  every  100  volumes  of  pure 
atmospheric  air,  79  volumes  (ou  an  average)  consist  of  nitrogen,  the  re- 
maining 21  of  oxygen.  By  weight  the  proportion  is  N.  75,  O.  25.  The 
proportion  of  carbonic  acid  is  extremely  small ;  10,000  volumes  of 
atmospheric  air  contain  only  about  4  or  5  of  carbonic  acid. 

The  quantity  of  watery  vapor  varies  greatly  according  to  the  tempera- 
ture and   other   circumstances,  but   the   atmosphere  is   never   without 


188  HANDBOOK   OF    PHYSIOLOGY. 

some.     In  this  country,  the  average  quantity  of  watery  vapor  in  the 
atmosphere  is  1.40  per  cent. 

Composition  of  Air  which  has  been  breathed. — The  changes  effected 
hy  respiration  in  the  atmospheric  air  are  :  1,  an  increase  of  temperature; 
2,  an  increase  in  the  quantity  of  carbonic  acid  ;  3,  a  diminution  in  the 
quantity  of  oxygen  ;  4,  a  diminution  of  volume  ;  5,  an  increase  in  the 
amount  of  watery  vapor  ;  6,  the  addition  of  a  minute  amount  of  organic 
matter  and  of  free  ammonia. 

1.  TJie  expired  air,  heated  by  its  contact  with  the  interior  of  the 
lungs,  is  (at  least  in  most  climates)  hotter  than  the  inspired  air.  Its 
temperature  varies  between  97°  and  99.5°  F.  (36°-37.5°  0.),  the  lower 
temperature  being  observed  when  the  air  has  remained  but  a  short  time 
in  the  lungs.  Whatever  may  be  the  temperature  of  the  air  when  in- 
haled, it  nearly  acquires  that  of  the  blood  before  it  is  expelled  from  the 
chest. 

2.  The  Carbonic  Acid  is  always  increased;  but  the  quantity  exhaled 
in  a  given  time  is  subject  to  change  from  various  circumstances.  From 
every  volume  of  air  inspired,  about  4.8  per  cent  of  oxygen  is  abstracted; 
while  a  rather  smaller  quantity,  4.3  of  carbonic  acid  is  added  in  its 
place  :  the  air  will  contain,  therefore,  434  vols,  of  carbonic  acid  in 
10,000.  Under  ordinary  circumstances,  the  quantity  of  carbonic  acid 
exhaled  into  the  air  breathed  by  a  healthy  adult  man  amounts  to  1346 
cubic  inches,  or  about  636  grains  per  hour.  According  to  this  estimate, 
the  weight  of  carbon  excreted  from  the  lungs  is  about  173  grains  per 
hour,  or  rather  more  than  8  ounces  in  twenty-four  hours.  These  quan- 
tities must  be  considered  approximate  only,  inasmuch  as  various  circum- 
stances, even  in  health,  influence  the  amount  of  carbonic  acid  excreted, 
and,  correlatively,  the  amount  of  oxygen  absorbed. 

Circumstances  influencing  the  amount  of  carbonic  acid  excreted. — 
The  following  are  the  chief  :— Age  and  sex.  Respiratory  movements. 
External  temperature.  Season  of  year.  Condition  of  respired  air. 
Atmospheric  conditions.  Period  of  the  day.  Food  and  drink.  Exer- 
cise and  sleep. 

a.  Age  and  Sex. — The  quantity  of  carbonic  acid  exhaled  into  the  air 
"breathed  by  males,  regularly  increases  from  eight  to  thirty  years  of  age  ; 

from  thirty  to  fifty  the  quantity,  after  remaining  stationary  for  a  while, 
gradually  diminishes,  and  from  fifty  to  extreme  age  it  goes  on  diminish- 
ing, till  it  scarcely  exceeds  the  quantity  exhaled  at  ten  years  old.  In 
females  (in  whom  the  quantity  exhaled  is  always  less  than  in  males  of 
the  same  age)  the  same  regular  increase  in  quantity  goes  on  from  the 
eighth  year  to  the  age  of  puberty,  when  the  quantity  abruptly  ceases  to 
increase,  and  remains  stationary  so  long  as  they  continue  to  menstruate. 
When  menstruation  has  ceased,  it  soon  decreases  at  the  same  rate  as  it 
does  in  old  men. 

b.  Respiratory  Movements. — The  more  quickly  the  movements  of 
respiration  are  performed,  the  smaller  is  the  proportionate  quantity  of 
carbonic  acid  contained  in  each  volume  of  the  expired  air.     Although, 


RESPIRATION.  1 89 

however,  the  proportionate  quantity  of  carbonic  acid  is  thus  diminished 
during  frequent  respiration,  yet  the  absolute  amount  exhaled  into  the 
air  within  a  given  time  is  increased  thereby,  owing  to  the  larger  quan- 
tity of  air  which  is  breathed  in  the  time.  The  last  half  of  a  volume  of 
expired  air  contains  more  carbonic  acid  than  the  half  first  expired  ;  a 
circumstance  which  is  explained  by  the  one  portion  of  air  coming  from 
the  remote  part  of  the  lungs,  where  it  has  been  in  more  immediate  and 
prolonged  contact  with  the  blood  than  the  other  has,  which  comes 
chiefly  from  the  larger  bronchial  tubes. 

c.  External  temperature. — The  observation  made  by  Vierordt  at  vari- 
ous temperatures  between  38°  F.  and  75°  F.  (3.4°-23.8°  C.)  show,  for 
warm-blooded  animals,  that  within  this  range,  every  rise  equal  to  10° 
F.,  causes  a  diminution  of  about  two  cubic  inches  in  the  quantity  of 
carbonic  acid  exhaled  per  miuute. 

d.  Season  of  the  Year. — The  season  of  the  year,  independently  of 
temperature,  materially  influences  the  respiratory  phenomena;  spring 
being  the  season  of  the  greatest,  and  autumn  of  the  least  activity  of  the 
respiratory  and  other  functions.     (Edward  Smith.) 

e.  Purity  of  the  Respired  Air. — The  average  quantity  of  carbonic 
acid  given  out  by  the  lungs  constitutes  about  4.3  per  cent  of  the  expired 
air;  but  if  the  air  which  is  breathed  be  previously  impregnated  with 
carbonic  acid  (as  is  the  case  when  the  same  air  is  frequently  respired), 
then  the  quantity  of  carbonic  acid  exhaled  becomes  much  less. 

f.  Hygrometric  State  of  Atmosphere. — The  amount  of  carbonic  acid 
exhaled  is  considerably  influenced  by  the  degree  of  moisture  of  the 
atmosphere,  much  more  being  given  off  when  the  air  is  moist  than  when 
it  is  dry.     (Lehmann.) 

().  Period  of  the  Day. — During  the  day-time  more  carbonic  acid  is 
exhaled  than  corresponds  to  the  oxygen  absorbed;  while,  on  the  other 
hand,  at  night  very  much  more  oxygen  is  absorbed  than  is  exhaled  in 
carbonic  acid.  There  is,  thus,  a  reserve  fund  of  oxygen  absorbed  by 
night  to  meet  the  requirements  of  the  day.  If  the  total  quantity  of 
carbonic  acid  exhaled  in  24  hours  be  represented  by  100,  52  parts  are  ex- 
haled during  the  day,  and  48  at  night.  While,  similarly,  33  parts  of  the 
oxygen  are  absorbed  during  the  day,  and  the  remaining  67  by  night. 
(Pettenkofer  and  Voit.) 

h.  Food  and  Drink. — By  the  use  of  food  the  quantity  is  increased, 
whilst  by  fasting  it  is  diminished;  it  is  greater  when  animals  are  fed  on 
farinaceous  food  than  when  fed  on  meat.  The  effects  produced  by 
spirituous  drinks  depend  much  on  the  kind  of  drink  taken.  Pure  alco- 
hol tends  rather  to  increase  than  to  lessen  respiratory  changes,  and  the 
amount  therefore  of  carbonic  acid  expired;  rum,  ale,  and  porter,  also 
sherry,  have  very  similar  effects.  On  the  other  hand,  brandy,  whiskey, 
and  gin,  particularly  the  latter,  almost  always  lessened  the  respiratory 
changes,  and  consequently  the  amount  of  carbonic  acid  exhaled.  (Ed- 
ward Smith.) 

i.  Exercise. — Bodily  exercise,  in  moderation,  increases  the  quantity 
to  about  one-third  more  than  it  is  during  rest:  and  for  about  an  hour 
after  exercise  the  volume  of  the  air  expired  in  the  minute  is  increased 
about  118  cubic  inches:  and  the  quantity  of  carbonic  acid  about  7.8  cubic 
inches  per  minute.  Violent  exercise,  such  as  full  labor  on  the  tread- 
wheel,  still  further  increases  the  amount  of  the  acid  exhaled.  (Edward 
Smith.) 


190  HANDBOOK    OF    PHYSIOLOGY. 

A  larger  quantity  is  exhaled  when  the  barometer  is  low  than  when  it 
is  high. 

3.  The  oxygen  is  diminished,  and  its  diminution  is  generally  propor- 
tionate to  the  increase  of  the  carbonic  acid. 

For  every  volume  of  carbonic  acid  exhaled  into  the  air,  1.17421 
volumes  of  oxygen  are  absorbed  from  it,  and  1346  cubic  inches,  or  63(5 
grains  being  exhaled  in  the  hour  the  quantity  of  oxygen  absorbed  in  the 
same  time  is  1584  cubic  inches  or  542  grains.  According  to  this  esti- 
mate, there  is  more  oxygen  absorbed  than  is  exhaled  with  carbon  to  form 
carbonic  acid. 

4.  The  volume  of  air  expired  in  a  given  time  is  less  than  that  of  the 
air  inspired  (allowance  being  made  for  the  expansion  in  being  heated), 
and  that  the  loss  is  due  to  a  portion  of  oxygen  absorbed  and  not  returned 
in  the  exhaled  carbonic  acid,  all  observers  agree,  though  as  to  the  actual 
quantity  of  oxygen  so  absorbed,  they  differ  even  widely.  The  amount 
of  oxygen  absorbed  is  on  an  average  of  4.8  per  cent,  so  that  the  expired 
air  contains  16.2  volumes  per  cent  of  that  gas. 

The  quantity  of  oxygen  that  does  not  combine  with  the  carbon  given 
off  in  carbonic  acid  from  the  lungs  is  probably  disposed  off  in  forming 
some  of  the  carbonic  acid  and  water  given  off  from  the  skin,  and  in 
combining  with  sulphur  and  phosphorus  to  form  part  of  the  acids  of  the 
sulphates  and  phosphates  excreted  in  the  urine,  and  probably  also  with 
the  nitrogen  of  the  decomposing  nitrogenous  tissues. 

The  quantity  of  oxygen  in  the  atmosphere  surrounding  animals 
appears  to  have  very  little  influence  on  the  amount  of  this  gas  absorbed 
by  them,  for  the  quantity  consumed  is  not  greater  even  though  an  excess 
of  oxygen  be  added  to  the  atmosphere  experimented  with. 

It  has  often  been  discussed  whether  Nitrogen  is  absorbed  by  or  ex- 
haled from  the  lungs  during  respiration.  At  present,  all  that  can  be 
said  on  the  subject  is  that,  under  most  circumstances,  animals  appear  to 
expire  a  very  small  quantity  above  that  which  exists  in  the  inspired  air. 
During  prolonged  fasting,  on  the  contrary,  a  small  quantity  appears  to 
be  absorbed. 

5.  The  ivatery  vapor  is  increased. — The  quantity  emitted  is,  as  a 
general  rule,  sufficient  to  saturate  the  expired  air,  or  very  nearly  so. 
Its  absolute  amount  is,  therefore,  influenced  by  the  following  circum- 
stances (1),  by  the  quantity  of  air  respired;  for  the  greater  this  is,  the 
greater  also  will  be  the  quantity  of  moisture  exhaled;  (2)  by  the  quantity 
of  watery  vapor  contained  in  the  air  previous  to  its  being  inspired;  be- 
cause the  greater  this  is,  the  less  will  be  the  amount  required  to  complete 
the  saturation  of  the  air;  (3)  by  the  temperature  of  the  expired  air;  for 
the  higher  this  is,  the  greater  will  be  the  quantity  of  watery  vapor  re- 
quired to  saturate  the  air;  (4)  by  the  length  of  time  which  each  volume  of 


RESPIRATION.  191 

inspired  air  is  allowed  to  remain  in  the  lungs;  for  although,  during 
ordinary  respiration,  the  expired  air  is  always  saturated  with  watery 
vapor,  yet  when  respiration  is  performed  very  rapidly  the  air  has  scarcely 
time  to  be  raised  to  the  highest  temperature,  or  be  fully  charged  with 
moisture  ere  it  is  expelled. 

The  quantity  of  water  exhaled  from  the  lungs  in  twenty-four  hours 
ranges  (according  to  the  various  modifying  circumstances  already  men- 
tioned) from  about  6  to  27  ounces,  the  ordinary  quantity  being  about  9 
or  10  ounces.  Some  of  this  is  probably  formed  by  the  chemical  combi- 
nation of  oxygen  with  hydrogen  in  the  system  ;  but  the  far  larger  pro- 
portion of  it  is  water  which  has  been  absorbed,  as  such,  into  the  blood 
from  the  alimentary  canal,  and  which  is  exhaled  from  the  surface  of  the 
air-passages  and  cells,  as  it  is  from  the  free  surfaces  of  all  moist  animal 
membranes,  particularly  at  the  high  temperature  of  warm-blooded  ani- 
mals. 

6.  A  small  quantity  of  ammonia  is  added  to  the  ordinary  constitu- 
ents of  expired  air.  It  seems  probable,  however,  both  from  the  fact 
that  this  substance  cannot  be  always  detected,  and  from  its  minute 
amount  when  present,  that  the  whole  of  it  may  be  derived  from  decom- 
posing particles  of  food  left  in  the  mouth,  or  from  carious  teeth  or  the 
like  ;  and  that  it  is,  therefore,  only  an  accidental  constituent  of  expired 
air. 

7.  The  quantity  of  organic  matter  in  the  breath  is  i ncreased  and  is 
about  3  grains  ii\  about  twenty-four  hours.     (Ransome.) 

Method  of  Experiment. — The  following  represents  the  kind  of  experi- 
ment by  which  the  foregoing  facts  regarding  the  excretion  of  carbonic 
acid,  water,  and  organic  matter,  have  been  established. 

A  bird  or  mouse  is  placed  in  a  large  bottle,  through  the  stopper  ol 
which  two  tubes  pass,  one  to  supply  fresh  air,  and  the  other  to  carry  off 
that  which  has  been  expired.  Before  entering  the  bottle,  the  air  is  made 
to  bubble  through  a  strong  solution  of  caustic  potash,  which  absorbs  the 
carbonic  acid,  and  then  through  lime-water,  which,  by  remaining  limpid, 
proves  the  absence  of  carbonic  acid.  The  air  which  has  been  breathed 
by  the  animal  is  made  to  bubble  through  lime-water,  which  at  once  be- 
comes turbid  and  soon  quite  milky  from  the  precipitation  of  calcium 
carbonate;  and  it  finally  passes  through  strong  sulphuric  acid,  which, 
by  turning  brown,  indicates  the  presence  of  organic  matter.  The 
watery  vapor  in  the  expired  air  will  condense  inside  the  bottle  if  the 
surface  be  kept  cool. 

By  means  of  an  apparatus  sufficiently  large  and  well-constructed, 
experiments  of  the  kind  have  been  made  extensively  on  man. 

Methods  by  which   the   Respiratory   Changes   in   the   Air  are 

effected. 

The  method  by  which  fresh  air  is  inhaled  and  expelled  from  the 
lungs  has  been  explained.     It  remains  to  consider  how  it  is  that  the 


192  HANDBOOK    OF    PHYSIO LOGY. 

blood  absorbs  oxygen  from,  and  gives  up  carbonic  acid  to,  the  air  of  the 
alveoli.  In  the  first  place,  it  must  be  remembered  that  the  tidal  air 
only  amounts  to  about  25-30  cubic  inches  at  each  inspiration,  and  that 
this  is  of  course  insufficient  to  fill  the  lungs,  but  it  mixes  with  the  sta- 
tionary air  by  diffusion,  and  so  supplies  to  it  new  oxygen.  The  amount 
of  oxygen  in  expired  air,  which  may  be  taken -as  the  average  composi- 
tion of  the  mixed  air  in  the  lungs,  is  about  16  to  17  per  cent ;  in  the 
pulmonary  alveoli  it  may  be  rather  less  than  this.  From  this  air  the 
venous  blood  has  to  take  up  oxygen  in  the  proportion  of  8  to  12  vols,  in 
every  hundred  volumes  of  blood,  as  the  difference  between  the  amount 
of  oxygen  in  arterial  and  venous  blood  is  no  less  than  that.  It  seems 
therefore  somewhat  diffcult  to  understand  how  this  can  be  accomplished 
at  the  low  oxygen  tension  of  the  pulmonary  air.  But  as  was  pointed 
out  in  a  previous  Chapter  (IV.),  the  oxygen  is  not  simply  dissolved  in 
the  blood,  but  is  to  a  great  extent  chemically  combined  with  the 
haemoglobin  of  the  red  corpuscles ;  and  when  a  fluid  contains  a  body 
which  enters  into  loose  chemical  combination  in  this  way  with  a  gas, 
the  tension  of  the  gas  in  the  fluid  is  not  directly  proportional  to  the 
total  quantity  of  the  gas  taken  up  by  the  fluid,  but  to  the  excess 
above  the  total  quantity  which  the  substance  dissolved  in  the  fluid  is 
capable  of  taking  up  (a  known  quantity  in  the  case  of  haemoglobin,  viz., 
1.59  cm.  for  one  gm.  haemoglobin).  On  the  other  hand,  if  the  sub- 
stance be  not  saturated,  i.  e.,  if  it  be  not  combined  with  as  much  of  the 
gas  as  it  is  capable  of  taking  up,  further  combination  leads  to  no  increase 
of  its  tension.  However,  there  is  a  point  at  which  the  haemoglobin 
gives  up  its  oxygen  when  it  is  exposed  to  alow  partial  pressure  of  oxygen, 
and  there  ks  also  a  point  at  which  it  neither  takes  up  nor  gives  out  oxy- 
gen ;  in  the  case  of  arterial  blood  of  the  dog,  this  is  found  to  be  when 
the  oxygen  tension  ©f  the  atmosphere  is  equal  to  3.9  per  cent  (29.6  mm. 
of  mercury),  which  is  equivalent  to  saying  that  the  oxygen  tension  of 
arterial  blood  is  3.9  per  cent;  venous  blood,  in  a  similar  manner,  has 
been  found  to  have  an  oxygen  tension  of  2.8  per  cent.  At  a  higher  tem- 
perature, the  tension  is  raised,  as  there  is  a  greater  tendency  at  a  high 
temperature  for  the  chemical  compound  to  undergo  dissociation.  It  is 
therefore  easy  to  see  that  the  oxygen  tension  of  the  air  of  the  pulmonary 
alveoli  is  quite  sufficient,  even  supposing  it  much  less  than  that  of  the 
expired  air,  to  enable  the  venous  blood  to  take  up  oxygen,  and  what  is 
more,  it  will  take  it  up  until  the  haemoglobin  is  very  nearly  saturated 
with  the  gas. 

As  regards  the  elimination  of  carbonic  acid  from  the  blood,  there  is 
evidence  to  show  that  it  is  given  up  by  a  process  of  simple  diffusion,  the 
only  condition  necessary  for  the  process  being  that  the  tension  of 
the  carbonic  acid  of  the  air  in  the  pulmonary  alveoli  should  be  less  than 
the  tension  of  the  carbonic  acid  in  venous  blood.     The  carbonic  acid 


RESPIRATION.  193 

tension  of  the  alveolar  air  probably  does  not  exceed  in  the  dog  3  or  4  per 
cent,  while  that  of  the  venous  blood  is  5.4  per  cent,  or  equal  to  41  mm. 
of  mercury. 

B.     In  the  Blood. 

Circulation  of  Blood  in  the  Respiratory  Organs. — To  be  exposed  to 
the  air  thus  alternately  moved  into  and  out  of  the  air-cells  and  minute 
bronchial  tubes,  the  blood  is  propelled  from  the  right  ventricle  through 
the  pulmonary  capillaries  in  steady  streams,  and  slowly  enough  to  per- 
mit every  minute  portion  of  it  to  be  for  a  few  seconds  exposed  to  the  air 
with  only  the  thin  walls  of  the  capillary  vessels  and  the  air-cells  inter- 
vening. The  pulmonary  circulation  is  of  the  simplest  kind  :  for  the 
pulmonary  artery  branches  regularly  ;  its  successive  branches  run  in 
straight  lines,  and  do  not  anastomose  :  the  capillary  plexus  is  uniformly 
spread  over  the  air-cells  and  intercellular  passages  ;  and  the  veins  derived 
from  it  proceed  in  a  course  as  simple  and  uniform  as  that  of  the  arteries, 
t  heir  branches  converging  but  not  anastomosing.  The  veins  have  no 
valves,  or  only  small  imperfect  ones  prolonged  from  their  angles  of  junc- 
tion, and  incapable  of  closing  the  orifice  of  either  of  the  veins  between 
which  they  are  placed.  The  pulmonary  circulation  also  is  unaffected  by 
changes  of  atmospheric  pressure,  and  is  not  exposed  to  the  influence  of 
the  pressure  of  muscles  :  the  force  by  which  it  is  accomplished,  and  the 
course  of  the  blood  are  alike  simple. 

Changes  in  the  Blood. — The  most  obvious  change  which  the  blood 
of  the  pulmonary  artery  undergoes  in  its  passage  through  the  lungs  is 
1st,  that  of  color,  the  dark  crimson  of  venous  blood  being  exchanged  for 
the  bright  scarlet  of  arterial  blood  ;  2d,  and  in  connection  with  the  pre- 
ceding change,  it  gains  oxygen  ;  3d,  it  loses  carbonic  acid  ;  4th,  it  be- 
comes slightly  cooler  ;  5th,  it  coagulates  sooner  and  more  firmly,  appar- 
ently containing  more  fibrin  The  oxygen  absorbed  into  the  blood  from 
the  atmospheric  air  in  the  lungs  is  combined  chemically  with  the  haemo- 
globin of  the  red-corpuscles.  In  this  condition  it  is  carried  in  the  arterial 
blood  to  the  various  parts  of  the  body,  and  brought  into  near  relation  or 
contact  with  the  tissues.  In  these  tissues,  and  in  the  blood  which  cir- 
culates in  them,  a  certain  portion  of  the  oxygen,  which  the  arterial 
blood  contains,  disappears,  and  a  proportionate  quantity  of  carbonic  acid 
and  water  is  formed.  The  venous  blood,  containing  the  new-formed 
carbonic  acid  returns  to  the  lungs,  where  a  portion  of  the  carbonic  acid 
is  exhaled,  and  a  fresh  supply  of  oxygen  is  taken  in. 

Mechanism  of  Various  Respiratory  Actions. 

It  will  be  well  here,  perhaps,  to  explain  some  respiratory  acts,  which 
appear  at  first  sight  somewhat  complicated,  but  cease  to  be  so  when  the 
mechanism  by  which  they  are  performed  is  clearly  understood.     The  ac- 
13 


191 


HANDBOOK    OF    PHYSIOLOGY. 


companying  diagram  (Fig.  160)  shows  that  the  cavity  of  the  chest  is 
separated  from  that  of  the  abdomen  by  the  diaphragm,  which,  when 
acting,  will  lessen  its  curve,  and  thus  descending,  will  push  downwards 
and  forwards  the  abdominal  viscera  ;  while  the  abdominal  muscles  have 
the  opposite  effect,  and  in  acting  will  push  the  viscera  upwards  and 
backwards,  and  with  them  the  diaphragm,  supposing  its  ascent  to  be 
not  from  any  cause  interfered  with.  From  the  same  diagram  it  will  be 
seen  that  the  lungs  communicate  with  the  exterior  of  the  body  through 


Fig.  160. 


the  glottis,  and  further  on  through  the  mouth  and  nostrils — through 
either  of  them  separately,  or  through  both  at  the  same  time,  according 
to  the  position  as  the  soft  palate.  The  stomach  communicates  with  the 
exterior  of  the  body  through  the  oesophagus,  pharynx,  and  mouth  ;  while 
below  the  rectum  opens  at  the  anus,  and  the  bladder  through  the  ure- 
thra. All  these  openings,  through  which  the  hollow  viscera  communi- 
cate with  the  exterior  of  the  body,  are  guarded  by  muscles,  called  sphinc- 
ters, which  can  act  independently  of  each  other.  The  position  of  the 
latter  is  indicated  in  the  diagram. 


RESPIRATION.  195 

Sighing. — In  sighing  there  is  a  rather  prolonged  inspiration ;  tlie 
air  almost  noiselessly  passing  in*  through  the  glottis,  and  by  the  elastic 
recoil  of  the  lungs  and  chest-walls,  and  probably  also  of  the  abdominal 
walls,  being  rather  suddenly  expelled  again. 

Now,  in  the  first,  or  inspiratory  part  of  this  act,  the  descent  of  the 
diaphragm  presses  the  abdominal  viscera  downwards,  and  of  course  this 
pressure  tends  to  evacuate  the  contents  of  such  as  communicate  with  the 
exterior  of  the  body.  Inasmuch,  however,  as  their  various  openings  are 
guarded  by  sphincter  muscles,  in  a  state  of  constant  tonic  contraction, 
there  is  no  escape  of  their  contents,  and  air  simply  enters  the  lungs.  In 
the  second,  or  expiratory  part  of  the  act  of  sighiug,  there  is  also  pressure 
made  on  the  abdominal  viscera  in  the  opposite  direction,  by  the  elastic 
or  muscular  recoil  of  the  abdominal  walls  ;  but  the  pressure  is  relieved 
by  the  escape  of  air  through  the  open  glottis,  and  the  relaxed  diaphragm 
is  pushed  up  again  into  its  original  position.  The  sphincters  of  the 
stomach,  rectum,  and  bladder,  act  in  the  same  manner  as  before. 

Hiccough  resembles  sighing  in  that  it  is  an  inspiratory  act  ;  but  the 
inspiration  is  sudden  instead  of  gradual,  in  consequence  of  the  diaphragm 
acting  suddenly  and  spasmodically  ;  and  the  air,  therefore  suddenly  rush- 
ing through  the  unprepared  rima  glottidis,  causes  vibration  of  the  vocal 
cords,  and  the  peculiar  sound. 

Coughing. — In  the  act  of  coughing,  there  is  most  often  first  of  all  a 
deep  inspiration,  followed  by  an  expiration  ;  but  the  latter,  instead  of 
being  easy  and  uninterrupted,  as  in  normal  breathing,  is  obstructed,  in 
consequence  of  the  glottis  being  momentarily  closed  by  the  approxima- 
tion of  the  vocal  cords.  The  abdominal  muscles,  then  strongly  acting, 
push  up  the  viscera  against  the  diaphragm,  and  thus  make  pressure  on 
the  air  in  the  lungs  until  its  tension  is  sufficient  to  noisily  burst  open  the 
vocal  cords  which  oppose  its  outward  passage.  In  this  way  considerable 
force  is  exercised,  and  mucus  or  any  other  matter  that  may  need  expul- 
sion from  the  air-passages  is  quickly  and  sharply  expelled  by  the  out- 
streaming  current  of  air. 

It  will  be  evident  on  reference  to  the  diagram  (Fig.  160),  that  pres- 
sure exercised  by  the  abdominal  muscles  in  the  act  of  coughing,  acts  as 
forcibly  on  the  abdominal  viscera  as  on  the  lungs,  inasmuch  as  the  viscera 
form  the  medium  by  which  the  upward  pressure  on  the  diaphragm  is 
made,  and  there  is  of  necessity  quite  as  great  a  tendency  to  the  expulsion 
of  their  contents  as  of  the  air  in  the  lungs.  The  instinctive,  and  H 
necessary,  voluntarily  increased  contraction  of  the  sphincters,  however, 
prevents  any  escape  at  the  openings  guarded  by  them,  and  the  pressure 
is  effective  at  one  part  only,  at  the  rima  glottidis. 

Sneezing. — The  same  remarks  that  apply  to  coughing,  are  almost 
exactly  applicable  to  the  act  of  sneezing  ;  but  in  this  instance  the  blast 
of  air,  on  escaping  from  the  lungs,  is  directed,  by  an  instinctive  contrac- 


198  HANDBOOK   OF    PHYSIOLOGY. 

tion  of  the  pillars  of  the  fauces  and  descent  of  the  soft  palate,  chiefly 
through  the  nose,  and  any  offending  matter  is  theuce  expelled. 

Speaking. — In  speaking,  there  is  a  voluntary  expulsion  of  air 
through  the  glottis  by  means  of  the  expiratory  muscles.  The  vocal 
cords  are  put,  by  the  muscles  of  the  larynx,  in  a  proper  position  and 
state  of  tension  for  vibrating  as  the  air  passes  over  them,  and  thus  sound 
is  produced.  The  sound  is  moulded  into  articulate  speech  by  the  tongue, 
teeth,  lips,  etc. — the  vocal  cords  producing  the  sound  only,  and  having 
nothing  to  do  with  articulation. 

Singing. — Singing  resembles  speaking  in  the  manner  of  its  produc- 
tion ;  the  laryngeal  muscles,  by  variously  altering  the  position  and  de- 
gree of  tension  of  the  vocal  cords,  producing  the  different  notes.  "Words 
used  in  the  act  of  singing  are  of  course  framed,  as  in  speaking,  by  the 
tongue,  teeth,  lips,  etc. 

Sniffing. — Sniffing  is  produced  by  a  rapidly  repeated  but  incomplete 
action  of  the  diaphragm  and  other  inspiratory  muscles.  The  mouth  is 
closed,  and  the  whole  stream  of  air  is  made  to  enter  the  air-passages 
through  the  nostrils.  The  alae  nasi  are,  commonly,  at  the  same  time, 
instinctively  dilated. 

Sobbing. — Sobbing  consists  of  a  series  of  convulsive  inspirations,  at 
the  moment  of  which  the  glottis  is  usually  more  or  less  closed.   « 

Laughing. — Laughing  is  made  up  of  a  series  of  short  and  rapid  ex- 
pirations. 

Yawning. — Yawning  is  an  act  of  inspiration,  but  is  unlike  most  of 
the  preceding  actions,  as  it  is  always  more  or  less  involuntary.  It  is 
attended  by  a  stretching  of  various  muscles  about  the  palate  and  lower 
jaw,  which  is  probably  analogous  to  the  stretching  of  the  muscles  of  the 
limbs  in  which  a  weary  man  finds  relief,  as  a  voluntary  act,  when  they 
have  been  some  time  out  of  action.  The  involuntary  and  reflex  char- 
acter of  yawning  probably  depends  on  the  fact  that  the  muscles  con- 
cerned are  themselves  at  all  times  more  or  less  used  involuntarily,  and 
require,  therefore,  something  beyond  the  exercise  of  the  will  to  set  them 
in  action.  For  the  same  reason,  yawning,  like  sneezing,  cannot  be  well 
performed  voluntarily. 

Sucking. — Sucking  is  not  properly  a  respiratory  act,  but  it  may  be 
most  conveniently  considered  in  this  place.  It  is  caused  chiefly  by  the 
depressor  muscles  of  the  os  hyoides.  These,  by  drawing  downwards  and 
backwards  the  tongue  and  floor  of  the  mouth,  produce  a  partial  vacuum 
in  the  latter  :  and  the  weight  of  the  atmosphere  then  acting  on  all  sides 
tends  to  produce  equilibrium  on  the  inside  and  outside  of  the  mouth  as 
best  it  may.  The  communication  between  the  mouth  and  pharynx 
is  completely  shut  off  by  the  contraction  of  the  pillars  of  the  soft  palate 
and  descent  of  the  latter  so  as  to  touch  the  back  of  the  tongue  ;  and  the 
equilibrium,  therefore,  can  be  restored  only  by  the  entrance  of  some- 


RESPIRATION.  197 

thing  through  the  mouth.  The  action,  indeed,  of  the  tongue  and  floor 
of  the  mouth  in  sucking  may  he  compared  to  that  of  the  piston  in  a 
syringe,  and  the  muscles  which  pull  down  the  os  hyoides  and  tongue,  to 
the  power  which  draws  the  handle. 

Influence  of  the  Nervous  System  in  Respiration. 

Like  all  other  functions  of  the  body,  the  discharge  of  which  is  neces- 
sary to  life,  respiration  is  essentially  an  involuntary  act.  Unless  this 
were  the  case,  life  would  be  in  coustant  danger,  and  would  cease  on  the 
loss  of  consciousness  for  a  few  moments,  as  in  sleep.  It  is,  however, 
also  necessary  that  respiration  should  be  to  some  extent  under  the  con- 
trol of  the  will.  For  were  it  not  so,  it  would  be  impossible  to  perform 
those  voluntary  respiratory  acts  which  have  been  just  discussed,  such  as 
speaking,  singing,  and  the  like. 

The  respiratory  movements  and  their  rhythm,  so  far  as  they  are  in- 
voluntary and  independent  of  consciousness,  as  they  are  on  all  ordinary 
occasions,  are  under  the  governance  of  a  nerve-centre  in  the  medulla 
oblongata  which  corresponds  in  position  with  the  origin  of  the  pneumo- 
gastric  nerves  ;  that  is  to  say,  the  muscles  concerned  in  the  respiratory 
movements,  are  excited  by  stimuli  which  issue  from  this  part  of  the 
nervous  system,  and  which  are  conveyed  by  the  various  motor  nerves 
supplying  the  muscles.  These  nerves  are  the  phrenics  and  intercostals 
chiefly.  On  division  of  one  phrenic,  for  example,  the  corresponding 
lialf  of  the  diaphragm  supplied  by  it  ceases  to  take  part  in  the  respira- 
tory movement,  and  on  division  of  both  nerves,  the  whole  muscle  ceases 
to  act.  Similarly,  division  of  the  intercostal  nerves  one  by  one  produces 
cessation  of  action  of  the  muscles  supplied  by  them.  To  what  extent 
the  medullary  centre  acts  automatically,  i.  e..  how  far  the  stimulus  orig- 
inates in  it,  or  how  far  it  is  merely  a  nerve-centre  for  reflex  action,  is 
not  certainly  known. 

It  is  clear,  however,  that  the  medullary  centre  is  bilateral  or  double, 
since  the  respiratory  movements  continue  after  the  medulla  at  this  point 
is  bisected  in  the  middle  line. 

There  is  considerable  evidence  in  favor  of  its  automatic  action.  Thus 
it  has  been  shown  that  if  the  spinal  cord  be  divided  below  the  medulla, 
so  that  no  afferent  impulses  can  reach  the  centre  from  below,  that  the 
nasal  and  laryngeal  respiration  continues.  The  only  possible  course  of 
the  afferent  impulses  would,  under  such  circumstances,  be  through  the 
cranial  nerves  ;  and  when  the  cord  and  medulla  are  intact  the  division 
of  these  nerves  produces  no  effect  upon  respiration,  and  indicates  that 
they  are  not  used  for  the  transmission  of  afferent  impulses  to  the  medul- 
lary centre.  It  appears  evident,  therefore,  that  afferent  stimuli  arc  not 
absolutely  necessary  for  maintaining  the  respiratory  movements.     The 


198  HANDBOOK    OF   PHYSIOLOGY. 

respiratory  centre,  although  automatic  in  its  action,  may,  however,  be 
reflexly  excited.  The  chief  channel  of  this  reflex  influence  is  the  vagus 
nerve,  for  when  the  nerve  of  one  side  is  divided,  respiration  is  slowed,, 
and  if  both  vagi  are  cut  it  becomes  still  slower. 

The  influence  of  the  vagus  trunk  upon  the  centre  may  be  twofold,. 
for  if  the  nerve  is  divided  below  the  origin  of  the  superior  laryngeal 
branch  and  the  central  end  is  stimulated,  respiratory  movements  are  in- 
creased in  rapidity,  and  indeed  follow  one  another  so  quickly  if  the 
stimuli  be  increased  in  number,  that  after  a  time  cessation  of  respiration 
iu  inspiration  takes  place  in  consequence  of  a  tetanus  of  the  respiratory 
muscles  (diaphragm).  Whereas  if  the  superior  laryngeal  branch  is  di- 
vided, although  no  effect,  or  scarcely  any,  follows  the  mere  division,  on 
stimulation  of  the  central  end  respiration  is  slowed,  and  after  a  time,  if 
the  stimulus  is  sufficiently  increased,  stops,  not  in  inspiration  as  in  the 
other  case,  but  in  expiration.  Thus  the  vagus  trunk  contains  fibres 
which  are  capable  of  slowing  and  fibres  which  are  capable  of  accelerating 
respiration.  The  theory  that  the  respiratory  centre  in  the  floor  of  the 
medulla  consists  of  two  parts,  one  of  which  tends  to  produce  inspiration 
and  the  other  to  produce  expiration,  is  very  plausible.  The  inspiratory 
part  of  the  centre  is  complementary  to  the  expiratory,  and  the  two  parts 
send  out  impulses  alternately.  If  we  adopt  this  theory,  we  must  look 
upon  the  main  trunk  of  the  vagus  as  aiding  the  inspiratory,  and  upon  the 
superior  laryngeal  as  aiding  the  expiratory  part  of  the  centre,  the  first 
nerve  possibly  inhibiting  the  action  of  the  expiratory  centre,  whilst  it 
aids  the  inspiratory,  and  the  latter  nerve  having  the  very  opposite  effect. 
But  inasmuch  as  the  respiration  is  slowed  on  division  of  the  vagi,  and 
not  quickened  or  manifestly  affected  at  all  on  simple  division  of  the  su- 
perior laryngeal,  it  must  be  supposed  that  the  vagi  fibres  are  always  in 
action,  but  that  the  superior  laryngeal  fibres  are  not. 

It  appears  that  there  are,  in  some  animals  at  all  events,  subordinate 
centres  in  the  spinal  cord  which  are  able,  under  certain  conditions,  to 
discharge  the  function  of  the  chief  respiratory  centre  in  the  medulla. 

The  centre  in  the  medulla  may  be  influenced  not  only  by  afferent  im- 
pulses proceeding  along  the  vagus  and  laryngeal  nerves  but  also  by  im- 
pulses passing  downward  from  the  cerebrum;  by  impressions  made  upon 
the  nerves  of  the  skin,  or  upon  part  of  the  fifth  nerve  distributed  to  the 
nasal  mucous  membrane;  or  upon  other  sensory  nerves.  Such  afferent 
influences  are  exemplified  in  the  deep  inspiration  excited  by  the  applica- 
tion of  cold  to  the  surface  of  the  skin,  and  by  the  production  of  sneezing 
on  the  slightest  irritation  of  the  nasal  mucous  membrane. 

At  the  time  of  birth,  the  separation  of  the  placenta,  and  the  conse- 
quent non-oxygenation  of  the  foetal  blood,  are  the  circumstances  which 
immediately  lead  to  the  issue  of  automatic  impulses  from  the  respiratory 
centre  in  the  medulla  oblongata. 


RESPIRATION.  190 

Methods  of  Stimulation  of  Respiratory  Centre. — The  means  by 
which  the  respiratory  centre  or  centres  are  stimulated  must  now  be  con- 
sidered. 

It  is  well  known  that  the  more  venous  the  blood,  the  more  marked 
are  the  inspiratory  impulses,  and  that  if  the  air  is  preveuted  from  enter- 
ing the  chest,  that  the  respiration  in  a  short  time  becomes  very  labored. 
The  obstruction  to  the  entrauce  of  air,  whether  partial  or  complete,  is 
followed  by  an  abnormal  rapidity  of  the  inspiratory  acts,  which  make  up 
even  in  depth  for  the  previous  stoppage.  The  condition  caused  by  the 
obstruction,  or  by  any  circumstance  in  consequence  of  which  the  oxygen 
of  the  blood  is  used  up  in  an  abnormally  quick  manner,  is  known  as 
dyspnoea,  and  as  the  aeration  of  the  blood  becomes  more  and  more  inter- 
fered with,  not  only  are  the  ordinary  respiratory  muscles  employed,  but 
also  those  extraordinary  muscles  which  have  been  previously  enumerated 
(p.  181).  As  the  blood  becomes  more  and  more  venous  the  action  of  the 
medullary  centre  becomes  more  and  more  active.  The  question  arises  as 
to  what  quality  of  the  venous  blood  it  is  which  causes  this  increased  ac- 
tivity ;  whether  it  is  its  deficiency  of  oxygen  or  its  excess  of  carbonic 
acid.  This  question  has  been  answered  by  the  experiments,  which  show 
on  the  one  hand  that  dyspnoea  occurs  when  there  is  no  obstruction  to  the 
exit  of  carbonic  acid,  as  when  an  animal  is  placed  in  an  atmosphere  of 
nitrogen,  and  that  it  cannot  therefore  be  due  to  the  accumulation  of  car- 
bonic acid  ;  and  on  the  other,  that  if  plenty  of  oxygen  is  supplied,  true 
dyspnoea  does  not  occur,  although  the  carbonic  acid  of  the  blood  is  in  ex- 
cess. It  is  highly  probable,  therefore,  that  the  respiratory  centre  is 
stimulated  to  action  by  the  absence  of  sufficient  oxygen  in  the  blood  cir- 
culating in  it,  and  not  by  the  presence  of  an  excess  of  carbonic  acid. 

The  means  by  which  the  vagus  is  excited  to  increase  the  activity  of 
the  respiratory  centre,  appears  to  be  that  the  venous  blood  circulating 
in  the  lungs,  or  the  air  in  tiie  pulmonary  alveoli,  stimulates  the  peri- 
pheral fibres  of  the  nerve.  If  these  be  the  stimuli  it  will  be  evident  that 
the  vagus  action  must  help  to  increase  the  activity  of  the  centre,  when 
the  blood  in  the  lungs  becomes  more  and  more  venous.  No  doubt  the 
venous  condition  of  the  blood  affects  all  the  sensory  nerves  in  a  similar 
manner.  It  has  been  shown  that  the  circulation  of  too  little  blood 
through  the  centre,  as  when  its  blood  supply  is  cut  off,  greatly  increases 
its  inspiratory  action. 

Effects  of  Vitiated  Air. — Ventilation. — As  the  air  expired  from 
the  lungs  contains  a  large  proportion  of  carbonic  acid  and  a  minute 
amount  of  organic  putrescible  matter,  it  is  obvious  that  if  the  same 
air  be  breathed  again  and  again,  the  proportion  of  carbonic  acid  ami 
organic  matter  will  constantly  increase  till  it  becomes  unfit  to  be  breathed, 
but  long  before  this  point  is  reached,  uneasy  sensations  occur,  such  as 
headache,  languor,  and  a  sense  of  oppression.     It  is  a  remarkable  fact. 


200  HANDBOOK    OF   PHYSIOLOGY. 

however,  that  the  organism  after  a  time  adapts  itself  to  such  a  vitiated 
atmosphere,  and  that  a  person  soon  comes  to  breathe,  without  sensible  in- 
convenience, an  atmosphere  which,  when  he  first  entered  it,  felt  intoler- 
able. Such  an  adaptation,  however,  can  only  take  place  at  the  expense 
of  a  depression  of  all  the  vital  functions,  which  must  be  injurious  if  long 
continued  or  often  repeated. 

This  power  of  adaptation  is  well  illustrated  by  the  experiments  of 
Claude  Bernard.  A  sparrow  is  placed  under  a  bell-glass  of  such  a  size 
that  it  will  live  for  three  hours.  If  now  at  the  end  of  the  second  hour 
(when  it  could  have  survived  another  hour)  it  be  taken  out  and  a  fresh 
healthy  sparrow  introduced,  the  latter  will  perish  instantly. 

It  must  be  evident  that  provision  for  a  constant  and  plentiful  supply 
of  fresh  air,  and  the  removal  of  that  which  is  vitiated,  is  of  far  greater 
importance  than  the  actual  cubic  space  per  head  of  occupants.  Not  less 
than  2000  cubic  feet  per  head  should  be  allowed  in  sleeping  apartments 
(barracks,  hospitals,  etc.),  and  with  this  allowance  the  air  can  only  be 
maintained  at  the  proper  standard  of  purity  by  such  a  system  of  venti- 
lation as  provides  for  the  supply  of  1500  to  2000  cubic  feet  of  fresh  air 
per  head  per  hour.     (Parkes.) 

The  Effect  of  Respiration  on  the  Circulation. 

The  heart  and  great  vessels  being  situated  in  the  air-tight  thorax, 
are  exposed  to  a  certain  alteration  of  pressure  when  the  capacity  of  the 
latter  is  increased  ;  for  although  the  expansion  of  the  lungs  during  in- 
spiration tends  to  counterbalance  this  increase  of  area,  it  never  does  so 
entirely,  since  part  of  the  pressure  of  the  air  which  is  drawn  into  the 
chest  through  the  trachea  is  expended  in  overcoming  the  elasticity  of 
the  lungs  themselves.  The  amount  thus  used  up  increases  as  the  lungs 
become  more  and  more  expanded,  so  that  the  pressure  inside  the  thorax 
during  inspiration,  as  far  as  the  heart  and  great  vessels  are  concerned, 
never  quite  equals  that  outside,  and  at  the  conclusion  of  inspiration  is 
considerably  less  than  the  atmospheric  pressure.  It  has  been  ascertained 
that  the  amount  of  the  pressure  used  up  in  the  way  above  described,  varies 
from  5  to  7  mm.  of  mercury  during  the  pause,  and  to  30  mm.  of  mer- 
cury when  the  lungs  are  expanded  at  the  end  of  a  deep  inspiration,,  so 
that  it  will  be  understood  that  the  pressure  to  which  the  heart  and  great 
vessels  are  subjected  diminishes  as  inspiration  progresses.  It  will  be 
understood  from  the  accompanying  diagram  how,  if  there  were  no  lungs 
in  the  chest,  but  if  its  capacity  were  increased,  the  effect  of  the  increase 
would  be  expended  in  pumping  blood  into  the  heart  from  the  veins,  but 
even  with  the  lungs  placed  as  they  are,  during  inspiration  the  pressure 
outside  the  heart  and  great  vessels  isdiminished,  and  they  have  therefore 
a  tendency  to  expand  and  to  diminish  the  intra-vascular  pressure.  The 
diminution  of  pressure  within  the  veins  passing  to  the  right  auricle  and 


RESPIRATION. 


201 


within  the  right  auricle  itself,  will  draw  the  blood  into  the  thorax,  and 
bo  assist  the  circulation.  This  suction  action  is  independent  of  the  suc- 
tion power  of  the  diastole  of  the  auricle  about  which  we  have  previously 
spoken  (p.  127).  The  effect  of  sucking  more  blood  into  the  right  auricle 
will,  cmteris  paribus,  increase  the  amount  passing  through  the  right 
ventricle,  which  also  exerts  a  similar  suction  action,  and  through  the 
lungs  into  the  left  auricle  and  ventricle  and  thus  into  the  aorta.  This 
all  tends  to  increase  the  arterial  tension.  The  effect  of  the  diminished 
pressure  upon  the  pulmonary  vessels  will  also  help  towards  the  same 
end,  t.  e.,  an  increased  flow  through  the  lungs,  so  that,  as  far  as  the 


Fig.  161. -Diagram  of  an  apparatus  illustrating  the  effect  of  inspiration  upon  the  heart  and 
great  vessels  within  the  thorax. -I,  the  thorax  at  rest;  H,  during  inspiration ;  n,  represents  the :0.1a- 
phragm  when  relaxed;  d\  when  contracted  (it  must  he  remembered  that  this  position  is  a  mere 
diagram),  i.  e.,  when  the  capacity  of  the  thorax  is  enlarged;  h,  the  heart;  y,the  veins  entering  11, 
and  a,  the  aorta;  rL  lJ,  the  right  and  left  lung;  t,  the  trachea;  M,  mercurial  manometer  in  connec- 
tion with  the  pleura.  The  increase  in  the  capacity  of  the  box  representing  the  thorax  isstenw 
dilate  the  heart  as  well  as  the  lungs,  and  so  to  pump  in  blood  through  v.  whereas  the  ^»£epreveires 
reflex  through  a.  The  position  of  the  mercury  in  m  shows  also  the  suction  which  is.  taking  piace. 
(Landois.) 

heart  and  its  veins  are  concerned,  inspiration  increases  the  blood  pres- 
sure in  the  arteries.  The  effect  of  inspiration  upon  the  aorta  and  its 
branches  within  the  thorax  would  be,  however,  contrary;  for  as  the  pres- 
sure outside  is  diminished  the  vessels  would  tend  to  expand,  and  thus  to 
diminish  the  tension  of  the  blood  within  them,  but  inasmuch  as  the  largo 
arteries  are  capable  of  little  expansion  beyond  their  natural  calibre,  the 
diminution  of  the  arterial  tension  caused  by  this  means  would  be  lnsuf- 


202  HANDBOOK   OF    PHYSIOLO&T. 

ficient  to  counteract  the  increase  of  arterial  tension  produced  by  the  ef- 
fect of  inspiration  upon  the  veins  ef  the  chest,  and  the  balance  of  the 
whole  action  would  be  in  favor  of  an  increase  of  arterial  tension  during 
the  inspiratory  period.  But  if  a  tracing  of  the  variation  be  taken  at  the 
same  time  that  the  respiratory  movements  are  being  recorded,  it  will  be 
found  that,  although  speaking  generally,  the  arterial  tension  is  increased 
during  inspiration,  the  maximum  of  arterial  tension  does  not  correspond 
with  the  acme  of  inspiration  (Fig.  162). 

As  regards  the  effect  of  expiration,  the  capacity  of  the  chest  is  dimin- 
ished, and  the  intra-thoracic  pressure  returns  to  the  normal,  which  is 
not  exactly  equal  to  the  atmospheric,  pressure.  The  effect  of  this  on 
the  veins  is  to  increase  their  intra-vascular  pressure,  and  so  to  diminish 
the  flow  of  blood  into  the  left  side  of  the  heart,  and  with  it  the  arterial 
tension,  but  this  is  almost  exactly  balanced  by  the  necessary  increase  of 


Fig.  162.  — Comparison  of  blood-pressure  curve  with  curve  of  intra-thoracic  pressure.  (To  be 
read  from  left  to  right.;  a  is  the  curve  of  blood-pressure  with  its  respiratory  undulations,  the  slow- 
er beats  on  the  descent  being  very  marked ;  b  is  the  curve  of  intra-thoracic  pressure  obtained  by 
connecting  one  limb  of  a  manometer  with  the  pleural  cavity.  Inspiration  begins  at  i  and  expiration 
at  e.  The  intra-thoracic  pressure  rises  very  rapidly  after  the  cessation  of  the  inspiratory  effort,  and 
then  slowly  falls  as  the  air  issues  from  the  chest;  at  the  beginning  of  the  inspiratory  effort  the  fall 
becomes  more  rapid.    (M.Foster.) 

arterial  tension  caused  by  the  increase  of  the  extra- vascular  pressure  of 
the  aorta  and  large  arteries,  so  that  the  arterial  tension  is  not  much 
affected  during  expiration  either  way.  Thus,  ordinary  expiration  does 
not  produce  a  distinct  obstruction  to  the  circulation,  as  even  when  the 
expiration  is  at  an  end  the  intra-thoracic  pressure  is  less  than  the  extra- 
thoracic. 

The  effect  of  violent  expiratory  efforts,  however,  has  a  distinct  action 
in  preventing  the  current  of  blood  through  the  lungs,  as  seen  in  the 
blueness  of  the  face  from  congestion  in  straining;  this  condition  being 
produced  by  pressure  on  the  small  pulmonary  vessels. 

We  may  summarize  this  mechanical  effect  of  respiration  on  the  blood- 
pressure  therefore,  and  say  that  inspiration  aids  the  circulation  and  so 
increases  the  arterial  tension,  and  that  although   expiration  does  not 


RESPIRATION. 


20J 


materially  aid  the  circulation,  yet  under  ordinary  conditions  neither  does 
it  obstruct  it.  Under  extraordinary  conditions,  however,  as  in  violent 
expirations,  the  circulation  is  decidedly  obstructed.  But  Ave  have  seen 
that  there  is  no  exact  correspondence  between  the  points  of  extreme 
arterial  tension  and  the  end  of  inspiration,  and  we  must  look  to  the  ner- 
vous system  for  an  explanation  of  this  apparently  contradictory  result. 

The  effect  of  the  nervous  system  in  producing  a  rhythmical  alteration 
of  the  blood-pressure  is  twofold.  In  the  first  place  the  cardio-inh  ibitory 
centre  is  believed  to  be  stimulated  during  the  fall  of  blood-pressure,  pro- 
ducing a  slower  rate  of  heart-beats  during  expiration,  which  will  be 


Fro  163  -Traube-Herine's  curves.    (To  be  read  from  left  to  right.)    The  curves  1,  2  3.  4.  and  6 
areJo&SsSdfr^^ 

so  that  the  several  curves  represent  successive  stages  of  the  same  exper  ran  Each  one  ,*  wace  i 
in  its  proper  position  relative  to  the  base  hne,  which  is  omitted;  g*J™*3S?w£m  arMfteMres- 

rapidly  8£  and  continued  to  fall  until  some  time  after  artificial  respiration  was  resumed.  ( M.  Fos- 
ter.) 

noticed  in  the  tracing  (Fig.  162).  The  undulations  during  the  de-line 
of  blood-pressure  being  longer  but  less  frequent,  this  effect  disappears 
when,  by  section  of  the  vagi,  the  effect  of  the  centre  is  cut  off  from  the 
heart;  and  in  the  second  place,  the  vasomotor  centre  is  also  believed  to 


304  HANDBOOK    OF    PHYSIOLOGY. 

send  out  rhythmical  impulses,  by  which  undulation  of  blood-pressure  is 
j) rod  need  independently  of  the  mechanical  effects  of  respiration. 

The  action  of  the  vaso-motor  centre  in  taking  part  in  produciug 
rhythmical  changes  of  blood-pressure  which  are  called  respiratory,  is 
shown  in  the  following  way: — In  an  animal  under  the  influence  of  urari, 
a  record  of  whose  blood-pressure  is  being  taken,  and  where  artificial  res- 
piration has  been  stopped,  and  both  vagi  cut,  the  blood-pressure  curve 
rises  at  first  almost  in  a  straight  line,  but  after  a  time  new  rhythmical 
undulations  occur  very  like  the  original  respiratory  undulations,  only 
somewhat  larger.  These  are  called  Tr (tube's  or  Travbe-Hering's  curves. 
These  continue  whilst  the  blood-pressure  continues  to  rise  and  only  cease 
when  the  vaso-motor  centre  and  the  heart  are  exhausted,  when  the 
pressure  speedily  falls.  These  curves  must  be  dependent  upon  the  vaso- 
motor centre,  as  the  mechauical  effects  of  respiration  have  been  elimi- 
nated by  the  poison  and  by  the  cessation  of  artificial  respiration,  and  the 
effect  of  the  cardio-inhibitory  centre  by  the  division  of  the  vagi.  It  may 
be  presumed  therefore  that  the  vaso-motor  centre,  as  well  as  the  cardio- 
inhibitory,  must  be  considered  to  take  part  with  the  mechanical  changes 
of  inspiration  and  expiration  in  producing  the  so-called  respiratory 
"undulations  of  blood-pressure. 

Cheyne- Stokes'  breathing. — This  is  a  rhythmical  irregularity  in  res- 
pirations which  has  been  observed  in  various  diseases,  and  is  especially 
connected  with  fatty  degeneration  of  the  heart.  Respirations  occur  in 
groups,  at  the  beginning  of  each  group  the  inspirations  are  very  shallow, 
but  each  successive  breath  is  deeper  than  the  preceding  until  a  climax  is 
reached,  after  which  the  inspirations  become  less  and  less  deep,  until  they 
cease  after  a  slight  pause  altogether. 

Apnoea. — Dyspnoea. — Asphyxia. 

As  blood  which  contains  a  normal  proportion  of  oxygen  sufficiently 
excites  the  respiratory  centre  (p.  199)  to  produce  normal  respiration, 
and,  as  the  excitement  and  consequent  respiratory  muscular  movements 
are  greater  {dyspnoea)  in  proportion  to  the  deficiency  of  this  gas,  so  an 
abnormally  large  proportion  of  oxygen  in  the  blood  leads  to  diminished 
breathing  movements,  and,  if  the  proportion  be  large  enough,  to  their 
temporary  cessation.  This  condition  of  absence  of  breathing  is  termed 
Apnoea,1  and  it  can  be  demonstrated,  in  one  of  the  lower  animals,  by 
performing  artificial  respiration  to  the  extent  of  saturating  the  blood 
with  oxygen. 

When,  on  the  other  hand,  the  respiration  is  stopped,  by,  e.g.,  inter- 
ference with  the  passage  of  air  to  the  lungs,  or  by  supplying  air  devoid 


1    This  term  has  been,  unfortunately,  often  applied  to  conditions  of  dyspnoea  or  as- 
jiliy.riu  ;  but  the  modern  application  of  the  term,  as  in  the  text,  is  the  more  convenient. 


RESPIRATION.  205 

of  oxygen,  a  condition  ensues,  which  passes  rapidly  from  Hyperpxcea 
(excessive  breathing)  to  the  state  of  Dyspnosa  (difficult  breathing),  and 
afterwards  to  Asphyxia  ;  and  the  latter  quickly  ends  in  death. 

The  ways  by  which  this  condition  of  asphyxia  may  be  produced  are 
very  numerous.  As,  for  example,  by  the  prevention  of  the  due  entry  of 
oxygen  into  the  blood,  either  by  direct  obstruction  of  the  trachea  or  other 
part  of  the  respiratory  passages,  or  by  introducing  instead  of  ordinary 
air  a  gas  devoid  of  oxygen,  or  by  interference  with  the  due  interchange 
of  gases  between  the  air  and  the  blood. 

Symptoms. — The  symptoms  of  asphyxia  may  be  divided  into  three 
groups,  which  correspond  with  the  stages  of  the  condition  which  are 
usually  recognized,  these  are  (1),  the  stage  of  exaggerated  breathing ; 
(2),  the  stage  of  convulsions  ;  (3),  the  stage  of  exhaustion. 

In  the  first  stage  the  patient  breathes  more  rapidly  and  at  the  same 
time  more  deeply  than  usual,  the  inspirations  at  first  being  especially  ex- 
aggerated and  prolonged.  The  muscles  of  extraordinary  inspiration  are 
called  into  action  and  the  effort  to  respire  is  labored  and  painful.  This 
is  soon  followed  by  a  similar  increase  in  the  expiratory  efforts,  which  be- 
come excessively  prolonged,  being  aided  by  all  the  muscles  of  extraordi- 
nary expiration.  During  this  stage,  which  lasts  a  varying  time,  from  a 
minute  upwards,  according  as  the  deprivation  of  oxygen  is  sudden  or 
gradual,  the  patient's  face  and  lips  become  blue,  his  eyes  are  prominent, 
and  his  expression  intensely  anxious.  The  prolonged  respirations  are 
accompanied  by  a  distinctly  audible  sound  ;  the  muscles  attached  to  the 
chest  stand  out  as  distinct  cords.  The  stage  includes  the  two  conditions 
hyperpnoea  and  dyspnoea  already  spoken  of.  It  is  due  to  the  increasingly 
powerful  stimulation  of  the  respiratory  centres  by  the  increasingly  venous 
blood. 

In  the  second  stage,  which  is  not  marked  out  by  any  distinct  line  of 
demarcation  from  the  first,  the  violent  expiratory  efforts  give  way  to 
general  convulsions  (in  men  and  other  warm-blooded  animals  at  any  rate), 
which  arise  from  the  further  stimulation  of  the  centres.  The  spasms  of 
the  muscles  are  those  of  the  body  in  general,  and  not  of  the  respiratory 
muscles  only.  The  convulsive  stage  is  a  short  one,  and  soon  passes  into 
the  third  stage,  of  exhaustion.  In  it,  the  respirations  all  but  cease,  the 
spasms  give  way  to  flaccidity  of  the  muscles,  the  patient  is  insensible,  the 
conjunctivae  are  insensitive  and  the  pupils  are  widely  dilated.  Every 
now  and  then  a  prolonged  sighing  inspiration  takes  place,  at  longer  and 
longer  intervals  until  they  cease  altogether,  and  the  patient  dies.  During 
this  stage  the  pulse  is  scarcely  to  be  felt,  but  the  heart  may  beat  for  some 
seconds  after  respirations  have  quite  ceased.  The  condition  is  due  to 
the  gradual  paralysis  of  the  respiratory  centre  by  the  prolonged  action 
of  the  increasingly  venous  blood. 

As  with  the  first  stage,  the  duration  of  the  second  and  third  stages 


206  HANDBOOK    OF    PHYSIOLOGY. 

depends  upon  the  manner  of  the  deprivation  of  oxj^gen,  whether  sudden 
or  gradual.  The  convulsive  stage  is  short,  lasting,  it  may  be,  only  one 
minute.     The  third  stage  may  last  three  minutes  and  upwards. 

The  circulatory  conditions  which  accompany  these  symptoms  are — 

(1)  More  or  less  interference  with  the  passage  of  the  blood  through 
the  pulmonary  blood-vessels. 

(2)  Accumulation  of  blood  in  the  right  side  of  the  heart  and  in  the 
systemic  veins. 

(3)  Circulation  of  impure  (non-aerated)  blood  in  all  parts  of  the 
body. 

Cause  of  death. — The  causes  of  these  conditions  and  the  manner  in 
which  they  act,  so  as  to  be  incompatible  with  life,  may  be  here  briefly 
considered. 

(1)  The  obstruction  to  the  passage  of  blood  through  the  lungs  is  not 
very  great ;  and  such  as  there  is  occurs  chiefly  in  the  later  stages  of 
asphyxia,  when,  by  the  violent  and  convulsive  action  of  the  expiratory 
muscles,  pressure  is  indirectly  made  upon  the  lungs,  and  the  circulation 
through  them  is  proportionately  interfered  with. 

(2)  Accumulation  of  blood,  with  consequent  distention  of  the  right 
side  of  the  heart  and  of  the  systemic  veins,  is  the  direct  result,  at  least 
in  part,  of  the  obstruction  to  the  pulmonary  circulation  just  referred  to. 
Other  causes,  however,  are  in  operation,  (a)  The  vaso-motor  centres 
stimulated  by  blood  deficient  in  oxygen,  causes  contraction  of  all  the 
small  arteries  with  increase  of  arterial  tension,  and  as  an  immediate 
consequence  the  filling  of  the  systemic  veins,  (b)  The  increased  arte- 
rial tension  is  followed  by  inhibition  of  the  action  of  the  heart,  and,  the 
heart,  contracting  less  frequently,  and  also  gradually  enfeebled  by  defi- 
cient supply  of  oxygen,  becomes  over-distended  with  blood  which  it 
cannot  expel.  At  this  stage  the  left  as  well  as  the  right  cavities  are 
over-distended. 

The  ill  effects  of  these  conditions  are  to  be  looked  for  parti}''  in  the 
heart,  the  muscular  fibres  of  which,  like  those  of  the  urinary  bladder  or 
any  other  hollow  muscular  organ,  may  be  paralyzed  by  over-stretching  ; 
and  partly  in  the  venous  congestion,  and  consequent  interference  with 
the  function  of  the  higher  nerve-centres,  especially  the  medulla 
oblongata. 

(3)  The  passage  of  non-aerated  blood  through  the  lungs  and  its  distri- 
bution over  the  body  are  events  incompatible  with  life  in  one  of  the 
higher  animals,  for  more  than  a  few  minutes  ;  the  rapidity  with  which 
death  ensues  in  asphyxia  being  due,  more  particularly,  to  the  effect  of 
non-oxygenized  blood  on  the  medulla  oblongata,  and,  through  the  coro- 
nary arteries,  on  the  muscular  substance  of  the  heart.  The  excitability 
of  both  nervous  and  muscular  tissue  is  dependent  on  a  constant  and 
large  supply  of  oxygen,  and,  when  this  is  interfered  with,  excitability  is 


RESPIRATION.  20  7 

rapidly  lost.  The  diminution  of  oxygen  has  a  more  direct  influence  in 
the  production  of  the  usual  symptoms  of  asphyxia  than  the  increased 
amount  of  carbonic  acid.  Indeed,  the  fatal  effect  of  a  gradul  accumu- 
lation of  the  latter  in  the  blood,  if  a  due  supply  of  oxygen  is  maintained, 
resembles  rather  that  of  a  narcotic  poison,  and  not  of  asphyxia. 

In  some  experiments  performed  by  a  committee  appointed  by  the 
Medico-Chirurgical  Society  to  investigate  the  subject  of  Suspended  Ani- 
mation, it  was  found  that,  in  the  dog,  during  simple  asphyxia,  i.  e.,  by 
simple  privation  of  air,  as  by  plugging  the  trachea,  the  average  duration 
of  the  respiratory  movements  after  the  animal  had  been  deprived  of  air, 
was  4  minutes  and  5  seconds  ;  the  extremes  being  3  minutes  30  seconds, 
and  4  minutes  40  seconds.  The  average  duration  of  the  heart's  action, 
on  the  other  hand,  was  7  minutes  11  seconds  ;  the  extremes  being  6 
minutes  40  seconds,  and  7  minutes  45  seconds.  It  would  seem,  there- 
fore, that  on  an  average,  the  heart's  action  continues  for  3  minutes  15 
seconds  after  the  animal  had  ceased  to  make  respiratory  efforts.  A  very 
similar  relation  was  observed  in  the  rabbit.  Eecovery  never  took  place 
after  the  heart's  action  had  ceased. 

The  results  obtained  by  the  committee  on  the  subject  of  drowning 
Ave  re  very  remarkable,  especially  in  this  respect,  that  whereas  an  animal 
may  recover,  after  simple  deprivation  of  air  for  nearly  four  minutes,  yet, 
after  submersion  in  water  for  1^  minutes,  recovery  seems  to  be  impos- 
sible. This  remarkable  difference  was  found  to  be  due,  not  to  the  mere 
submersion,  nor  directly  to  the  struggles  of  the  animal,  nor  to  depres- 
sion of  temperature,  but  to  the  two  facts,  that  in  drowning,  a  free  pas- 
sage is  allowed  to  air  out  of  the  lungs,  and  a  free  entrance  of  water  into 
them.  It  is  probably  to  the  entrance  of  water  into  the  lungs  that  the 
speedy  death  in  drowning  is  mainly  due.  The  results  of  post-mortem 
examination  strongly  support  this  view.  On  examination  the  lungs  of 
animals  deprived  of  air  by  plugging  the  trachea,  they  were  found 
simply  congested  ;  but  in  the  animals  drowned,  not  only  was  the  con- 
gestion much  more  intense,  accompanied  with  ecchvmosed  points  on  the 
surface  and  in  the  substance  of  the  lung,  but  the  air  tubes  were  com- 
pletely choked  up  with  a  sanious  foam,  consisting  of  blood,  water,  and 
mucus,  churned  up  with  the  air  in  the  lungs  by  the  respiratory  efforts 
of  the  animal.  The  lung-substance,  too,  appeared  to  be  saturated  and 
sodden  with  water,  which,  stained  slightly  with  blood,  poured  out  at  any 
point  where  a  section  was  made.  The  lung  thus  sodden  with  water  was 
heavy  (though  it  floated),  doughy,  pitted  on  pressure,  and  was  incapable 
of  collapsing.  It  is  not  difficult  to  understand  how,  by  such  infarction 
of  the  tubes,  air  is  debarred  from  reaching  the  pulmonary  cells  ;  indeed 
the  inability  of  the  lungs  to  collapse  on  opening  the  chest  is  a  proof  of 
the  obstruction  which  the  froth  occupying  the  air-tubes  offers  to  the 
transit  of  air. 

We  must  carefully  distinguish  the  asphyxiating  effect  of  an  insuffi- 
cient supply  of  oxygen  from  the  directly  poisonous  action  of  such  gases 
as  carbonic  oxide,  which  is  contained  to  a  considerable  amount  in  com- 
mon coal-gas.  The  fatal  effects  often  produced  by  this  gas  (as  in  acci- 
dents from  burning  charcoal  stoves  in  small,  close  rooms),  are  due  to  its 
entering  into  combination  with  the  haemoglobin  of  the  blood-corpuscles 
(p.  87).  and  thus  expelling  the  oxyen. 


CHAPTER  VI. 

FOODS  AND   DIET. 

IN"  order  that  life  of  the  individual  may  be  maintained  it  is  neces- 
sary that  his  body  should  be  supplied  with  food  in  proper  quality  and 
quantity. 

The  food  taken  in  by  the  animal  body  is  used  for  the  purpose  of  re- 
placing the  waste  of  the  tissues.  In  order  to  arrive,  therefore,  at  a 
reasonable  estimation  of  the  proper  diet  required  in  the  twenty-four 
hours,  it  is  essential  that  we  should  know  the  amount  and  composition 
of  the  excreta  daily  eliminated  from  the  body.  Careful  analysis  of  the 
excreta  shows  that  they  are  made  up  chiefly  of  the  chemical  elements, 
carbon,  hydrogen,  oxygen,  and  nitrogen,  but  that  they  also  contain  to  a 
less  extent,  sulphur,  phosphorus,  chlorine,  potassium,  sodium,  and 
certain  other  of  the  elements.  Since  this  is  the  case  it  must  be  evident 
that,  to  balance  this  waste,  foods  must  be  supplied  containing  all  these 
elements  to  a  certain  degree,  and  some  of  them,  viz.,  those  which  take  a 
principal  part  in  forming  the  excreta,  in  large  amount. 

Of  the  excreta  we  have  seen  in  the  last  Chapter  that  carbonic  acid 
and  ammonia,  which  are  made  up  of  the  elements,  carbon,  oxygen, 
nitrogen,  hydrogen,  are  given  off  from  the  lungs.  By  the  excretion  of 
the  kidneys — the  urine — many  elements  are  eliminated  from  the  blood, 
especially  nitrogen,  hydrogen,  and  oxygen.  In  the  sweat,  the  elements 
chiefly  represented  are  carbon,  hydrogen,  and  oxygen,  and  also  in  the 
faeces.  By  all  the  excretions  large  quantities  of  water  are  got  rid  of 
daily,  but  chiefly  by  the  urine. 

The  relations  between  the  amounts  of  the  chief  elements  contained 
in  these  various  excreta  in  twenty-four  hours  may  be  thus  summarized : 


Water. 

C. 

H. 

N. 

O. 

By  the  lungs.   . . 
By  the  skin. .   . . 
By  the  urine 

330 

660 

1700 

128 

248.8 
2.6 
9  8 
20. 

"3'3 
3 

1 

ih'.s 

3. 

651.15 

7.2 
11.1 
12. 

2818 

281  2 

6.3 

18.8 

681.41 

FOODS    AND    DIET.  209 

To  this  should  be  added  29G.  grammes  water,  which  are  produced  by 
the  union  of  hydrogen  and  oxygen  in  the  body  during  the  process  of 
oxidation  (i.  e.,  32.80  hydrogen  and  2G3  11  oxygen).  There  are  twenty- 
six  grammes  of  salts  got  rid  of  by  the  urine  and  six  by  the  fseces. 

The  quantity  of  carbon  daily  lost  from  the  body  amounts  to  about 
281.2  grammes  or  nearly  4,500  grains,  and  of  nitrogen  18.8  grammes  or 
nearly  300  grains;  and  if  a  man  could  be  fed  by  these  elements,  as  such, 
the  problem  would  be  a  very  simple  one;  a  correspondhig  Aveight  of 
charcoal,  and,  allowing  for  the  oxygen  in  it,  of  atmospheric  air,  would 
be  all  that  is  necessary.  But  an  animal  can  live  only  upon  these  ele- 
ments when  they  are  arranged  in  a  particular  manner  with  others,  in  the 
form  of  an  organic  compound,  as  albumen,  starch,  and  the  like;  and  the 
relative  proportion  of  carbon  to  nitrogen  in  either  of  these  compounds 
alone,  is,  by  no  means,  the  proportion  required  in  the  diet  of  man. 
Thus,  in  albumen,  the  proportion  of  carbon  to  nitrogen  is  only  as  3.5  to 
1.  If,  therefore,  a  man  took  into  his  body,  as  food,  sufficient  albumen 
to  supply  him  with  the  needful  amount  of  carbon,  he  would  receive  more 
than  four  times  as  much  nitrogen  as  he  wanted;  and  if  he  took  only 
sufficient  to  supply  him  with  nitrogen,  he  would  be  starved  for  want  of 
carbon.  It  is  plain,  therefore,  that  he  should  take  with  the  albuminous 
part  of  his  food,  which  contains  so  large  a  relative  amount  of  nitrogen 
in  proportion  to  the  carbon  he  needs,  substances  in  which  the  nitrogen 
exists  in  much  smaller  quantities  relatively  to  the  carbon. 

It  is  therefore  evident  that  the  diet  must  consist  of  several  sub- 
stances, not  of  one  alone,  and  we  must  therefore  turn  to  the  available 
food  stuffs.  For  the  sake  of  convenience  they  may  be  classified  as 
under: 

A.  ORGANIC. 

I.  Nitrogenous,  consisting   of   Proteids,  e.g.,  albumen,    casein, 

syntonin,  gluten,  legumin  and  their  allies  ;  and  Gelatins. 
which  include  gelatin,  elastin,  and  chondrin.  All  of  these 
contain  carbon,  hydrogen,  oxygen,  and  nitrogen  and  some  in 
addition,  P.  and  S. 

II.  Non-Nitrogenous,  comprising  : 

(1.)  Amyloid  or  saccharine  bodies,  chemically  known  as  carbo-hy- 
drates, since  they  contain  carbon,  hydrogen,  and  oxygen,  with 
the  last  two  elements  in  the  proportion  to  form  water,  i.e., 
H,jnOn.     To  this  class  belongs  starch  and  sugar. 

(2.)  Oils  and  fats. — These  contain  carbon,  hydrogen,  and  oxygen, 
but  the  oxygen  is  less  in  amount  than  in  the  amyloids  and 
saccharine  bodies. 

B.  INORGANIC. 

I.  Mineral  and  saline  matter. 

II.  Water. 

14 


210  HANDBOOK    OF    PHYSIOLOGY. 

To  supply  the  loss  of  nitrogen  and  carbon,  it  is  found  by  experience 
that  it  is  necessary  to  combine  substances  which  contain  a  large  amount 
of  nitrogen  with  others  in  which  carbon  is  in  considerable  amount ;  and 
although,  without  doubt,  if  it  were  possible  to  relish  and  digest  one  or 
other  of  the  above-mentioned  proteids  when  combined  with  a  due  quan- 
tity of  an  amyloid  to  supply  the  carbon,  such  a  diet,  together  with  salt 
and  water,  ought  to  support  life  ;  yet  we  find  that  for  the  purposes  of 
ordinary  life  this  S3rstem  does  not  answer,  and  instead  of  confining  our 
nitrogenous  foods  to  one  variety  of  substance  we  obtain  it  in  a  large 
number  of  allied  substances,  for  example,  in  flesh,  of  bird,  beast,  or  fish; 
in  eggs ;  in  milk ;  and  in  vegetables.  And,  again,  we  are  not  content 
with  one  kind  of  material  to  supply  the  carbon  necessary  for  maintaining 
life,  but  seek  more,  in  bread,  in  fats,  in  vegetables,  in  fruits.  Again, 
the  fluid  diet  is  seldom  supplied  in  the  form  of  pure  water,  but  in  beer, 
in  wines,  in  tea  and  coffee,  as  well  as  in  fruits  and  succulent  vegetables. 

Man  requires  that  his  food  should  be  cooked.  Very  few  organic  sub- 
stances can  be  properly  digested  without  previous  exposure  to  heat  and 
to  other  manipulations  which  constitute  the  process  of  cooking. 

A. — Foods  containing  nitrogenous  principles  chiefly. 

I. — Flesh  of  Animals,  of  the  ox  (beef,  veal),  sheep  (mutton,  lamb), 
pig  (pork,  bacon,  ham). 

Of  these,  beef  is  richest  in  nitrogenous  matters,  containing  about  20 
per  cent,  whereas  mutton  contains  about  18  per  cent,  veal,  16.5,  and 
pork,  10  ;  the  flesh  is  also  firmer,  more  satisfying,  and  is  supposed  to  be 
more  strengthening  than  mutton,  whereas  the  latter  is  more  digestible. 
The  flesh  of  young  animals,  such  as  lamb  and  veal,  is  less  digestible  and 
less  nutritious.  Pork  is  comparatively  indigestible  and  contains  a  large 
amount  of  fat. 

Flesh  contains  : — (1)  Nitrogenous  bodies  :  myosin,  serum-albumin, 
gelatin  (from  the  interstitial  fibrous  connective  tissue);  elastiu  (from  the 
elastic  tissue),  as  well  as  hcemoglobin.  (2)  Fatty  matters,  including 
lecithin  and  cliolesterin.  (3)  Extractive  matters,  some  of  which  are 
agreeable  to  the  palate,  e.g.,  osmazome,  and  others,  which  are  weakly 
stimulating,  e.g.,  kreatin.  Besides,  there  are  sarcolactic  and  inositic 
acids,  taurin,  xanthin,  and  others.  (4)  Salts,  chiefly  of  potassium,  cal- 
cium, and  magnesium.  (5)  Water,  the  amount  of  which  varies  from  15 
per  cent  in  dried  bacon  to  39  in  pork,  51  to  53  in  fat  beef  and  mutton, 
to  72  per  cent  in  lean  beef  and  mutton.  (6)  A  certain  amount  of  carbo- 
hydrate material  is  found  in  the  flesh  of  some  animals,  in  the  form  of 
inosite,  dextrin,  grape  sugar,  and  (in  young  animals)  glycogen. 


foods  and  diet.  211 

Table  of  Percentage  Composition*  of   Beef,  Mutton,  Pork  and 

Veal  — (Letheby.) 


Water. 

Albumen. 

Fats. 

Salt 

Beef. — Lean,  . 

72 

19.3 

3.6 

5.1 

Fat, 

.    51 

14.8 

29.8 

4.4 

Mutton. — Ljean, 

72 

18.3 

4.9 

4.8 

Fat,     . 

.    53 

12.4 

31.1 

3.5 

Veal, 

63 

16.5 

15.8 

4.7 

Pork.- Fat, 

.    39 

9.8 

48.9 

2.3 

Together  with  the  flesh  of  the  above-mentioned  animals,  that  of  the 
deer,  hare,  rabbit,  and  birds,  constituting  venison,  game,  and  poultry, 
should  be  added  as  taking  part  in  the  supply  of  nitrogenous  substances, 
and  also  fish — salmon,  eels,  etc.,  and  shell-fish,  e.g.,  lobster,  crab,  mus- 
sels, oysters,  shrimps,  scollops,  cockles,  etc. 

Table    of    Percentage    Composition    of    Poultry    and    Fish. — 

(Letheby.) 

Water.  Albumen.  Fats.  Salts. 

Poultry,     ....       74  21  3.8  1.2 

(Singularly  devoid  of  fat,  and  is  therefore  generally  eaten  with  bacon 
or  pork. ) 

Water. 

White  Fish,  78 

Salmon,       ....     77 
Eels  (verv  rich  in  fat),     .         75 
Oysters,       .         .         .         .75.74 
(7.39  consist  of  non-nitrogenous  matter  and  loss.) 

Even  now  the  list  of  fleshy  foods  is  not  complete,  as  the  flesh  of 
nearly  all  animals  has  been  occasionally  eaten,  and  we  may  presume  that 
except  for  difference  of  flavor,  etc.,  the  average  composition  is  nearly  tlue 
same  in  every  case. 

II.  Milk. — Is  intended  as  the  entire  food  of  young  animals,  and  as 
such  contains,  when  pure,  all  the  elements  of  a  typical  diet.  (1)  Albu- 
minous substances  in  the  form  of  casein  and  serum-albumin.  (2)  Fats 
in  the  cream.  (3)  Carbohydrates  in  the  form  of  lactose  or  milk  sugar. 
(4)  Salts,  chiefly  calcium  phosphate  ;  and  (5)  Water.  From  it  we  obtain 
(a)  cheese,  which  is  the  casein  precipitated  with  more  or  less  of  fat 
according  as  the  cheese  is  made  of  skim  milk  (skim  cheese),  or  of  fresh 
milk  with  its  cream  (Cheddar  and  Cheshire),  or  of  fresh  milk  plus 
cream  (Stilton  and  double  Gloucester).  The  precipitated  casein  is 
allowed  to  ripen,  by  which  process  some  of  the  albumen  is  split  up,  with 
formation  of  fat.  (/?)  Cream,  consists  of  the  fatty  globules  incased  in 
casein,  and  which  being  of  low  specific  gravity  float  to  the  surface.  (;') 
Butter,  or  the  fatty  matter  deprived  of  its  casein  envelope  by  the  process 


Albumen. 

Fats. 

Salts. 

18.1 

2.9 

1. 

16.1 

5.5 

1.4 

9.9 

13.8 

1.3 

11.72 

2.42 

2.73 

and  loss.) 

(Payen.) 

212  HANDBOOK    OF    PHYSIOLOGY. 

of  churning.  (6)  Butter-milk,  or  the  fluid,  obtained  from  cream  after 
butter  has  been  formed;  very  rich  therefore  in  nitrogen,  (s)  JYhey,  or 
the  fluid  which  remains  after  the  precipitation  of  casein;  it  contains 
sugar,  salt,  and  a  small  quantity  of  albumen. 

Table  of  Composition"  of  Milk,  Butter-milk,  Cream,  and 
Cheese. — (Letheby  and  Payen.) 

Nitrogenous  matters.     Fats.     Lactose.     Salts.     Water. 
Milk  (Coiv), 
Butter -milk, 
Cream, 

Cheese. — Skim, 
11  Cheddar, 


"     Neufchatel  (fresh),  8.  40.71       36.58        .51     36.58 

III.  Eggs. — The  yelk  and  albumen  of  eggs  are  in  the  same  relation 
as  food  for  the  embryoes  of  oviparous  animals  that  milk  is  to  the  young 
of  mammalia,  and  afford  another  example  of  the  natural  admixture  of 
the  various  alimentary  principles. 

Table  of  the  Percentage  Composition  of  Fowls'  Eggs. 


4.1 

3.9 

5.2 

.8 

86 

4.1 

.7 

6.4 

.8 

88 

2.7 

26.7 

2.8 

1.8 

Q6 

44.8 

6.3 

— 

4.9 

44 

28.4 

31.1 

— 

4.5 

36 

Non-nitrogenous 

matter  and  loss. 

Nitrogenous  substances. 

Fats. 

Salts. 

Water. 

White,     . 

20.4 

— 

1.6 

78 

Yelk, 

16. 

30.7 

1.3 

52 

IV.  Leguminous  fruits  are  used  by  vegetarians,  as  the  chief  source 
of  the  nitrogen  of  the  food.  Those  chiefly  used  are  peas,  beans,  lentils, 
etc.,  they  contain  a  nitrogenous  substance  called  legumin,  allied  to  albu- 
men. They  contain  about  25.30  per  cent  of  this  nitrogenous  body,  and 
twice  as  much  nitrogen  as  wheat. 

B.  Foods  containing  carbohydrate  bodies  chiefly. 

I.  Bread,  made  from  the  ground  grain  obtained  from  various  so- 
called  cereals,  viz.,  wheat,  rye,  maize,  barley,  rice,  oats,  etc.,  is  the 
direct  form  in  which  the  carbohydrate  is  supplied  in  an  ordinary  diet. 
Flour,  however,  besides  the  starch,  contains  gluten,  a  nitrogenous  body, 
and  a  small  amount  of  fat. 

Table  of  Percentage  Composition  of  Bread  and  Flour. 

Nitrogenous  matters.     Carbohydrates.     Fats.     Salts.     Water. 
Bread,         .         .         8.1  51.  1.6       2.3        37 

Flour,      .         .  10.8  70.85  2.         1.7        15 

Various  articles  of  course  besides  bread  are  made  from  flour,  e.  g., 
sago,  macaroni,  biscuits,  etc. 


FOODS    AND    DIET.  213 

II.  Vegetables,  especially  potatoes.     They  contain  starch  and  sugar. 

III.  Fruits  contain  sugar,  and  organic  acids,  tartaric,  malic,  citric, 
and  others. 

C.  Substances  supplying  fatty  bodies  principally. 
The  chief  are  butter,  lard  (pig's  fat),  suet  (beef  and  mutton  fat). 

D.  Substances  supplying  the  salts  of  the  food. 

Nearly  all  the  foregoing  substances  in  A,  B,  and  C,  contain  a  greater 
or  less  amount  of  the  salts  required  in  food,  but  green  vegetables 
and  fruits  supply  certain  salts,  without  which  the  normal  health  of  the 
body  cannot  be  maintained. 

E.  Liquid  foods. 

Water  is  consumed  alone,  or  together  with  certain  other  substances 
used  to  flavor  it,  e.g.,  tea,  coffee,  etc.  Tea  in  moderation  is  a  stimulant, 
and  contains  an  aromatic  oil.  to  which  it  owes  its  peculiar  aroma,  an  as- 
tringent of  the  nature  of  tanuin,  and  an  alkaloid,  theine.  The  compo- 
sition of  coffee  is  very  nearly  similar  to  that  of  tea.  Cocoa,  in  addition 
to  similar  substances  contained  in  tea  and  coffee,  contains  fat,  albuminous 
matter,  and  starch,  and  must  be  looked  upon  more  as  a  food. 

Beer,  in  various  forms,  is  an  infusion  of  malt  (barley  which  has 
sprouted,  and  in  which  its  starch  is  converted  in  great  part  into  sugar), 
boiled  with  hops  and  allowed  to  ferment.  Beer  contains  from  1.2  to  8.8 
per  cent  of  alcohol. 

Cider  and  Perry,  the  fermented  juice  of  the  apple  and  pear. 

Wine,  the  fermented  juice  of  the  grape,  contains  from  6  or  7  (Rhine 
wines,  and  white  and  red  Bordeaux)  to  24-25  (ports  and  sherries)  per 
cent  of  alcohol. 

Spirits,  obtained  from  the  distillation  of  fermented  liquors.  They 
contain  upwards  of  40-70  per  cent  of  absolute  alcohol. 

Effects  of  cooking  upon  Food. 

In  general  terms  this  may  be  said  to  make  food  more  easily  digestible; 
this  usually  implies  two  alterations — food  is  made  more  agreeable  to  the 
palate  and  also  more  pleasing  to  the  eye.  Cooking  consists  in  exposing 
the  food  to  various  degrees  of  heat,  either  to  the  direct  heat  of  the  fire, 
as  in  roasting,  or  to  the  indirect  heat  of  the  fire,  as  in  broiling,  baking, 
or  frying,  or  to  hot  water,  as  in  boiling  or  stewing.  The  effect  of  heat 
upon  (a)  flesh  is  to  coagulate  the  albumen  and  coloring  matter,  to  solid- 
ify fibrin,  and  to  gelatinize  tendons  and  fibrous  connective  tissue.  Pre- 
vious beating  or  bruising  (as  with  steaks  and  chops),  or  keeping  (as  in 
the  case  of  game),  renders  the  meat  more  tender.     Prolonged  exposure 


21i  HANDBOOK    OF    FH\SIOLOGY= 

to  heat  also  develops  on  the  surface  certain  empyreumatic  bodies,  which 
are  agreeable  both  to  the  taste  and  smell.  By  placing  meat  in  hot  water, 
the  external  coating  of  albumen  is  coagulated,  and  very  little,  if  any,  of 
the  constituents  of  the  meat  are  lost  afterwards  if  boiling  be  prolonged; 
but  if  the  constituents  of  the  meat  are  to  be  extracted,  it  should  be  ex- 
posed to  prolonged  simmering  at  a  much  lower  temperature,  and  the 
"broth"  will  then  contain  the  gelatin  and  extractive  matters  of  the 
meat,  as  well  as  a  certain  amount  of  albumen.  The  addition  of  salt  will 
help  to  extract  myosin. 

The  effect  of  boiling  upon  (b)  an  egg  is  to  coagulate  the  albumen,  and 
this  helps  to  render  the  article  of  food  more  suitable  for  adult  dietary. 
Upon  (c)  milk,  the  effect  of  heat  is  to  produce  a  scum  composed  of  al- 
bumen and  a  little  casein  (the  greater  part  of  the  casein  being  uncoag- 
ulated)  with  some  fat.  Upon  (d)  vegetables,  the  cooking  produces  the 
necessary  effect  of  rendering  them  softer,  so  that  they  can  be  more 
readily  broken  up  in  the  mouth;  it  also  causes  the  starch  grains  to  swell 
up  and  burst,  and  so  aids  the  digestive  fluids  in  penetrating  into  their 
substance.  The  albuminous  matters  are  coagulated,  and  the  gummy, 
saccharine  and  saline  matters  are  removed.  The  conversion  of  flour  into 
dough  is  effected  by  mixing  it  with  water,  and  adding  a  little  salt  and  a 
certain  amount  of  yeast.  Yeast  consists  of  the  cells  of  an  organized 
ferment  (Torula  cerevisice),  and  it  is  by  the  growth  of  this  plant,  which, 
lives  upon  the  sugar  produced  from  the  starch  of  the  flour,  that  a  quan- 
tity of  carbonic  acid  gas  and  alcohol  is  formed.  By  means  of  the  former 
the  dough  rises.  Another  method  of  making  dough  consists  in  mixing 
the  flour  with  water  containing  a  large  quantity  of  carbonic  acid  gas  in 
solution. 

By  the  action  of  heat  during  baking  (tl)  the  dough  continues  to  ex- 
pand, and  the  gluten  being  coagulated,  the  bread  sets  as  a  permanently 
vesiculated  mass, 

I. — Effects  of  an  insufficent  diet. 

Hunger  and  Thirst. — The  sensation  of  hunger  is  manifested  in  con- 
sequence of  deficiency  of  food  supplied  to  the  system.  The  mind  refers 
the  sensation  to  the  stomach;  yet  since  the  sensation  is  relieved  by  the 
introduction  of  food  either  into  the  stomach  itself,  or  into  the  blood 
through  other  channels  than  the  stomach,  it  would  appear  not  to  depend 
on  the  state  of  the  stomach  alone.  This  view  is  confirmed  by  the  fact, 
that  the  division  of  both  pneumogastric  nerves,  which  are  the  principal 
channels  by  which  the  brain  is  cognizant  of  the  condition  of  the  stomach, 
does  not  appear  to  allay  the  sensations  of  hunger.  But  that  the  stomach 
has  some  share  in  this  sensation  is  proved  by  the  relief  afforded,  though 
only  temporarily,  by  the  introduction  of  even  non-alimentary  substances 


FOODS    AND    DIET.  21 


D 


into  this  organ.  It  may,  therefore,  be  said  that  the  sensation  of  hunger 
is  caused  both  by  a  want  in  the  system  generally,  and  also  by  the  condi- 
tion of  the  stomach  itself,  by  which  condition,  of  course,  its  own  nerves 
are  more  directly  affected. 

The  sensation  of  third,  indicating  the  want  of  fluid,  is  referred  to 
the  fauces,  although,  as  in  hunger,  this  is,  in  great  part,  only  the  local 
declaration  of  a  general  condition.  For  thirst  is  relieved  for  only  a  very 
short  time  by  moistening  the  dry  fauces  ;  but  may  be  relieved  completely 
by  the  introduction  of  liquids  into  the  blood,  either  through  the  stomach, 
by  injections  into  the  blood-vessels,  or  by  absorption  from  the  surface  of 
the  skin  or  the  intestines.  The  sensation  of  thirst  is  perceived  most 
naturally  whenever  there  is  a  disproportionately  small  quantity  of  water 
in  the  blood  :  as  well,  therefore,  when  water  has  been  abstracted  from 
the  blood,  as  when  saline  or  any  solid  matters  have  been  abundantly 
added  to  it.  And  the  cases  of  hunger  and  thirst  are  not  the  only  ones 
in  which  the  mind  derives,  from  certain  organs,  a  peculiar  predominant 
sensation  of  some  condition  affecting  the  whole  body.  Thus,  the  sensa- 
tion of  the  "  necessity  of  breathing."  is  referred  especially  to  the  air- 
passages  ;  but,  as  Yolkmann's  experiments  show,  it  depends  on  the  con- 
dition of  the  blood  which  circulates  everywhere,  and  is  felt  even  after 
the  lungs  of  animals  are  removed  :  for  they  continue,  even  then,  to  gasp 
and  manifest  the  sensation  of  want  of  breath. 

Starvation. — The  effects  of  total  deprivation  of  food  have  been  made 
the  subject  of  experiments  on  the  lower  animals,  and  have  been  but  too 
frequently  illustrated  in  man.  (1)  One  of  the  most  notable  effects  of 
starvation,  as  might  be  expected,  is  loss  of  weight ;  the  loss  being  great- 
est at  first,  as  a  rule,  but  afterwards  not  varying  very  much,  day  by  day, 
until  death  ensues.  Chossat  found  that  the  ultimate  proportional  loss 
was,  in  different  animals  experimented  on,  almost  exactly  the  same  ; 
death  occurring  when  the  body  had  lost  two-fifths  (forty  per  cent)  of  its 
original  weight.  Different  parts  of  the  body  lose  weight  in  very  differ- 
ent proportions.  The  following  results  are  taken,  in  round  numbers, 
from  the  table  given  by  M.  Chossat : — 

Fat  loses,   ....     93  per  cent.  '  Liver  loses,     ...     52  per  cent. 

Blood, 75  "  "         Heart, 44    "      " 

Spleen,       .     .     .     .     71  "  "  I  Intestines,      ...     42    "      " 

Pancreas,      .     .     .     .  64  "  "         Muscles  of  locomotion,42    "      " 

Stomach  loses,     .     .     39  "  "         Respiratory  apparatus, 22    "      " 

Pharynx,  (Esophagus,  34  "  "         Bones, 16    "      " 

Skin,        .....  3:}  "  "  |  Eyes, 10    "       " 

Kidneys  lose,        .     .     31  "  "  |  Nervous  System,    .     .     2  (nearly.) 

(2.)  The  effect  of  starvation  on  the  temperature  of  the  various  ani- 
mals experimented  on  by  Chossat  was  very  marked.  For  some  time  the 
variation  in  the  daily  temperature  was  more  marked  than  its  absolute 
and  continuous  diminution,  the  daily  fluctuation  amounting  to  5°  or  6° 


21fl  HANDBOOK    OF    PHYSIOLOGY. 

F.  (3°  O.j,  instead  of  1°  or  2°  F.  (.5°  to  1°  C.),  as  in  health.  But  a 
short  time  before  death,  the  temperature  fell  very  rapidly,  and  death 
ensued  when  the  loss  had  amounted  to  about  30°  F.  (16.2°  C).  It  has 
been  often  said,  and  with  truth,  although  the  statement  requires  some 
qualification,  that  death  by  starvation  is  really  death  by  cold  ;  for  not 
only  has  it  been  found  that  difference  of  time  with  regard  to  the  period 
of  the  fatal  result  are  attended  by  the  same  ultimate  loss  of  heat,  but 
the  effect  of  the  application  of  external  warmth  to  animals  cold,  and  dy- 
ing from  starvation,  is  more  effectual  in  reviving  them  than  the  admin- 
istration of  food.  In  other  words,  an  animal  exhausted  by  deprivation 
of  nourishment  is  unable  so  to  digest  food  as  to  use  it  as  fuel,  and  there- 
fore is  dependent  for  heat  on  its  supply  from  without. 

(3.)  The  symptoms  produced  by  starvation  in  the  human  subject  are 
hunger,  accompanied,  or  it  may  be  replaced,  by  pain,  referred  to  the 
region  of  the  stomach  ;  insatiable  thirst ;  sleeplessness  ;  general  weak- 
ness and  emaciation.  The  exhalations  both  from  the  lungs  and  skin  are 
foetid,  indicating  the  tendency  to  decomposition  which  belongs  to  badly- 
nourished  tissues  ;  and  death  occurs,  sometimes  after  the  additional  ex- 
haustion caused  by  diarrhoea,  often  with  symptoms  of  nervous  disorder, 
delirium  or  convulsions. 

(4.)  In  the  human  subject  death  commonly  occurs  within  six  to  ten 
days  after  total  deprivation  of  food.  But  this  period  may  be  consider- 
ably prolonged  by  taking  a  very  small  quantity  of  food,  or  even  water 
only.  The  cases  so  frequently  related  of  survival  after  many  days,  or 
even  some  weeks,  of  abstinence,  have  been  due  either  to  the  last-men- 
tioned circumstances,  or  to  others  no  less  effectual,  which  prevented  the 
loss  of  heat  and  moisture.  Cases  in  which  life  has  continued  after  total 
abstinence  from  food  aud  drink  for  many  weeks,  or  months,  exist  only 
in  the  imagination  of  the  vulgar. 

(5.)  The  appearances  presented  after  death  from  starvation  are  those 
of  general  wasting  and  bloodlessness,  the  latter  condition  being  least  no- 
ticeable in  the  brain.  The  stomach  and  intestines  are  empty  and  con- 
tracted, and  the  walls  of  the  latter  appear  remarkably  thinned  and 
almost  transparent.  The  various  secretions  are  scanty  or  absent,  with 
the  exception  of  the  bile,  which,  somewhat  concentrated,  usually  fills 
the  gall-bladder.     All  parts  of  the  body  readily  decompose. 

II. — Effects  of  Improper  Diet. 

Experiments  on  Feeding. — Experiments  illustrating  the  ill-effects 
produced  by' feeding  animals  upon  one  or  two  alimentary  substances  only 
have  been  often  performed. 

Dogs  were  fed  exclusively  on  sugar  and  distilled  water.  During  the 
first  seven  or  eight  days  they  were  brisk  and  active,  and  took  their  food 


FOODS    AND    DIET.  217 

and  drink  as  usual  ;  but  in  the  course  of  the  second  week  they  began  to 
get  thin,  although  their  appetite  continued  good,  and  they  took  daily 
between  seven  and  eight  ounces  of  sugar.  The  emaciation  increased 
during  the  third  week,  and  they  became  feeble,  and  lost  their  activity 
and  appetite.  At  the  same  time  an  ulcer  formed  on  each  cornea,  followed 
by  an  escape  of  the  humors  of  the  eye  :  this  took  place  in  repeated  ex- 
periments. The  animals  still  continued  to  eat  three  or  four  ounces  of 
sugar  daily  ;  but  became  at  length  so  feeble  as  to  be  incapable  of  motion 
and  died  on  a  day  varying  from  the  thirty-first  to  the  thirty-fourth.  On 
dissection,  their  bodies  presented  all  trie  appearances  produced  by  death 
from  starvation  ;  indeed,  dogs  will  live  almost  the  same  length  of  time 
without  any  food  at  all. 

"When  dogs  were  fed  exclusively  on  gum,  results  almost  similar  to  the 
above  ensued.  "When  they  were  kept  on  olive  oil  and  water,  all  the  phe- 
nomena produced  were  the  same,  except  that  no  ulceration  of  the  cornea 
took  place  ;  the  effects  were  also  the  same  with  butter.  The  experi- 
ments of  Chossat  and  Letellier  prove  the  same  ;  and  in  men,  the  same 
is  shown  by  the  various  diseases  to  which  those  who  consume  but  little 
nitrogenous  food  are  liable,  and  especially  by  the  affection  of  the  cornea 
which  is  observed  in  Hindus  feeding  almost  exclusively  on  rice.  But  it 
]s  not  only  the  non-nitrogenous  substances,  which,  taken  alone,  are  in- 
sufficient for  the  maintenance  of  health.  The  experiments  of  the  Acad- 
emies of  France  and  Amsterdam  were  equally  conclusive  that  gelatin 
alone  soon  ceases  to  be  nutritive. 

III.— Effect  of  Too  Much  Food. 

Sometimes  the  excess  of  food  is  so  great  that  it  passes  through  the 
alimentary  canal,  and  is  at  once  got  rid  of  by  increased  peristaltic  action 
of  the  intestines.  In  other  cases,  the  unabsorbed  portions  undergo  putre- 
factive changes  in  the  intestines,  which  are  accompanied  by  the  produc- 
tion of  gases,  such  as  carbonic  acid,  carbu retted  and  sulphuretted 
hydrogen,  and  a  distended  condition  of  the  bowels,  together  with  symp- 
toms of  indigestion,  is  the  result.  An  excess  of  the  substances  required 
as  food  may  undergo  absorption.  It  is  a  well-known  fact  that  numbers 
of  people  habitually  eat  too  much,  and  especially  of  nitrogenous  food. 
Dogs  can  digest  an  immense  amount  of  meat  if  fed  often,  and  the  amount 
of  meat  taken  by  some  men  would  supply  not  only  the  nitrogen,  but  also 
the  carbon  which  is  requisite  for  an  ordinary  natural  diet.  A  method 
of  getting  rid  of  an  excess  of  nitrogen  is  provided  by  the  digestive  pro- 
cesses in  the  duodenum,  to  be  presently  described,  whereby  the  excess  of 
the  albuminous  food  is  capable  of  being  changed  before  absorption  into 
nitrogenous  crystalline  matters  easily  converted  into  urea  and  so  easily 
excreted  by  the  kidneys,  affording  one  variety  of   what   is  called  luxus 


218  HANDBOOK   OF    PHYSIOLOGY. 

consumption  ;  but  no  doubt  after  a  time  the  organs,  especially  the  liver 
upon  "which  the  extra  amount  of  the  ingested  diet  throws  most  of  the 
stress,  will  yield  to  the  strain  of  the  over-work,  and  will  not  reduce  the 
excess  of  nitrogenous  material  brought  to  it  into  urea,  but  into  other 
less  oxidized  products,  such  as  uric  acid  ;  general  plethora,  aud  gout 
being  the  result.  This  state  of  things,  however,  is  delayed  for  a  long 
time,  if  not  altogether  obviated,  when  large  meat-eaters  take  a  considera- 
ble amount  of  exercise. 

Excess  of  carbohydrate  food  produces  an  accumulation  of  fat,  which 
may  not  only  be  an  inconvenience  by  causing  obesity,  but  may  interfere 
with  the  proper  nutrition  of  muscles,  causing  a  feebleness  of  the  action 
of  the  heart,  and  other  troubles.  The  accumulation  of  fat  is  due  to  the 
excess  of  carbohydrate  being  stored  up  by  the  protoplasm  in  the  form  of 
fat.  Starches  when  taken  in  great  excess  are  almost  certain  to  give  rise 
to  dyspepsia,  with  acidity  and  flatulence.  Excess  of  starch  or  of  sugar 
in  the  food  may,  however,  be  got  rid  of  by  the  urine  in  the  form  of  gly- 
cosuria. There  is  evidently  a  limit  to  the  absorption  of  starch  and  of 
fat,  as,  if  taken  beyond  a  certain  amount,  they  appear  unchanged  in  the 
faeces. 

Requisites  of  a  Normal  Diet. 

It  will  have  been  understood  that  it  is  necessary  that  a  normal  diet 
should  be  made  up  of  various  articles,  that  they  should  be  well  cooked, 
and  that  they  should  contain  about  the  same  amount  of  carbon  and  ni- 
trogen as  are  got  rid  of  by  the  excreta.  No  doubt  these  desiderata  may 
be  satisfied  in  many  ways,  and  it  would  be  unreasonable  to  expect  that 
the  diet  of  every  adult  should  be  unvarying.  The  age,  sex,  strength,  and 
circumstances  of  each  individual  must  ultimately  determine  his  diet.  A 
dinner  of  bread  and  hard  cheese  with  an  onion  contains  all  the  requisites 
for  a  meal,  but  such  diet  would  be  suitable  only  for  those  possessing 
strong  digestive  powers.  It  is  a  well-known  fact  that  the  diet  of  the 
continental  nations  differs  from  that  of  our  own  country,  and  that  of 
cold  from  that  of  hot  climates,  but  the  same  principle  underlies  them  all, 
viz.,  the  replacement  of  the  loss  of  the  excreta  in  the  most  convenient 
and  economical  way  possible.  Without  going  into  detail  in  the  matter 
it  may  be  said  that  any  one  in  active  work  requires  more  nitrogenous 
matter  than  one  at  rest,  and  that  children  and  women  require  less  than 
adult  men. 

The  quantity  of  food  for  a  healthy  adult  man  of  average  height  and 
weight  may  be  stated  in  the  following  table: — 


foods  and  diet.  21  ^ 

Table  of  Food  requieed  for  a  Healthy  Adult.  (Parkes.) 

For  laborious  At  reg 
occupation. 

Nitrogenous  substances,  e.</.,  flesh,  .         6     to  7     oz.  av.       2.5  oz. 

Fats,    .         .         .         .         .            .        3.5  to  4. 5  oz.  1      oz. 

Carbo-hydrates,        .         .         .                16    to  18   oz.  12     o 

Salts,            ....            .        1.2  to  1.5  oz.  .5  oz. 


26.7  to  31  oz.  16      oz. 

The  above  table  contains  the  weights  of  dry  or  solid  food  required. 
Such  food  is  found  in  practice  to  be  nearly  always  combined  with  50  to 
60  per  cent  of  water,  and  so  the  above  numbers  should  be  correspond- 
ingly increased.  The  amount  of  liquids  required  in  addition  is  about 
three  pints  per  diem. 

Full  diet  scale  for  an  adult  male  in  hospital  (St.  Bartholomeiu's 

Hospital). 

Breakfast. — 1  pint  of  tea  (with  milk  and  sugar),  bread  and  butter. 
Dinner. — ^lb.  of  cooked  meat, -Hb.  potatoes,  bread  and  beer. 
Tea. — 1  pint  of  tea,  bread  and  butter. 
Svpper. — Bread  and  butter,  beer. 

Daily  allowance  to  each  patient. — 2  pints  of  tea,  with  milk  and  sugar; 
14  oz.  bread;  ^lb.  cooked  meat;  -^  lb.  potatoes;  2  pints  of  beer;  loz.  but- 
ter; 31  oz.  solid,  and  4  pints  (80  oz. ),  liquid. 


CHAPTER    VII. 


DIGESTION. 


The  object  of  digestion  is  to  prepare  the  food  to  supply  the  waste  of 
the  tissues,  which  we  have  seen  is  its  proper  function  in  the  economy. 
Few  of  the  articles  of  diet  are  taken  in  the  exact  condition  in  which  it 
is  possible  for  them  to  be  absorbed  into  the  system  by  the  blood-vessels 
and  lymphatics,  without. which  they  would  be  useless'for  the  purposes 
they  have  to  fulfil.  Almost  the  whole  of  the  food,  therefore,  undergoes 
various  digestive  changes  before  it  is  fit  for  absorption.  Having  been 
received  into  the  mouth,  it  is  subjected  to  the  action  of  the  teeth  and 
tongue,  and  is  mixed  with  the  first  of  the  digestive,  juices — the  saliva.  It 
is  then  swallowed,  and,  passing  through  the  pharynx  and  oesophagus  into 
the  stomach,  is  subjected  to  the  action  of  the  gastric  juice — the  second 
digestive  juice.  Thence  it  passes  into  the  intestines,  where  it  meets  with 
the  bile,  the  pancreatic  juice,  and  the  intestinal  juices,  all  of  which  exer- 
cise an  influence  upon  the  portion  of  the  food  not  absorbed  in  the  stomach. 
By  this  time  most  of  the  food  is  capable  of  absorption,  and  the  residue 
of  undigested  matter  leaves  the  body  in  the  form  of  fceces  by  the  anus. 

The  course  of  the  food  through  the  alimentary  canal  of  man  will  be 
readily  seen  from  the  accompanying  diagram  (Fig.  164). 

The  Mouth  is  the  cavity  contained  between  the  jaws  and  inclosed 
by  the  cheeks  laterally,  the  lips  anteriorly;  behind  it  opens  into  the  pha- 
rynx by  the  fauces,  and  is  separated  from  the  nasal  cavity  above,  by  the 
hard  palate  in  front,  and  the  soft  palate  behind,  which  forms  its  roof. 
The  tongue  forms  the  lower  part  or  floor.  In  the  jaws  are  contained 
the  teeth,  and  when  the  mouth  is  shut  these  form  its  anterior  bounda- 
ries. The  whole  of  the  mouth  is  lined  with  mucous  membrane,  covered 
with  stratified  squamous  epithelium,  which  is  continuous  in  front  along 
the  lips  with  the  epithelium  and  the  skin,  and  posteriorly  with  that  of 
the  pharynx.  The  mucous  membrane  is  provided  with  numerous  glands 
(small  tubular),  called  mucous  glands,  and  into  it  open  the  ducts  of  the 
salivary  glands,  three  chief  glands  on  each  side.  The  tongue  is  not  only 
a  prehensile  organ,  but  is  also  the  chief  seat  of  the  sense  of  taste. 

We  shall  first  of  all  devote  some  little  space  to  the  consideration  of 
the  structure  and  develojmient  of  the  teeth,  and  then  shall  proceed  to 


DIGESTION. 


221 


discuss,  in  detail,  the  process  of  digestion,  as  it  takes  place  in  each  stage 
of  the  journey  of  food  through  the  alimentary  canal. 


Fig.  164.— Diagram  of  the  Alimentary  Canal.    The  small  intestine  of  man  is  from  about  3  to  4 
times  as  long  as  the  large  intestine. 

The  Teeth. 

During  the  course  of  his  life,  man  in  common  with  other  mammals, 
is  provided  with  two  sets  of  teeth,  the  first  set  is  called  the  temporary  or 
milk  teeth,  which  makes  its  appearance  in  infancy,  and  is  in  the  course  of 
a  few  years  shed  and  replaced  by  the  second  or  permanent  set. 

The  temporary  or  milk  teeth  have  only  a  very  limited  term  of 
existence. 

They  are  ten  in  number  in  each  jaw,  namely,  on  either  side  from  the 
middle  line  two  incisors,  one  canine,  and  two  deciduous  molars,  and  are 
replaced  by  ten  permanent  teeth. 

The  number  of  permanent  teeth  in  each  jaw  is,  however,  increased  to 
sixteen,  by  the  development  of  three  others  on  each  side  of  the  iaw. 


HANDBOOK    OF   PHYSIOLOGY, 


The  following  formula  shows,  at  a  glance,  the  comparative  arrange- 
ment and  number  of  the  temporary  and  permanent  teeth  : — 

Dec.  Mo.  Ca.     In.    Ca.    Mo. 


Temporary  Teeth. 


Permanent  Teeth. 


(Upper         2       14       1 


=  10 


(  Lower         2       14       1 


:20 


=  10 


Bicuspids 
or  Prse- 


True 
Molars.  Molars 

C  Upper    3         2 
(  Lower     3         2 


Ca. 
1 


In. 
4 


Ca. 
1 


Bi. 

2 


Mo. 

3  =  16 
=32 


14  12  3  =  16 
From  this  formula  it  will  be  seen  that  the  two  bicuspid  or  praemolar 
teeth  in  the  adult  are  the  successors  of  the  two  deciduous  molars  in  the 
child.  They  differ  from  them,  however,  in  some  respects,  the  temporary 
molars  having  a  stronger  likeness  to  the  permanent  than  to  their  imme- 
diate descendants,  the  so-called  bicuspids. 


Fig.  165.— Part  of  the  lower  jaw  of  a  child  of  three  or  four  years  old,  showing  the  relations  of 
the  temporary  and  permanent  teeth.  The  specimen  contains  all  the  milk-teeth  of  the  right  side, 
together  with  the  incisors  of  the  left;  the  inner  plate  of  the  jaw  has  been  removed,  so  as  to  expose 
the  sacs  of  all  the  permanent  teeth  of  the  right  side,  except  the  eighth  or  wisdom  tooth,  which  is 
not  yet  formed.  The  large  sac  near  the  ascending  ramus  of  the  jaw  is  that  of  the  first  permanent 
molar,  and  above  and  behind  it  is  the  commencing  rudiment  of  the  second  molar.    (Quain.) 

The  temporary  incisors  and  canines  differ  from  their  successors  but 
little  except  in  their  smaller  size. 

The  following  tables  show  the  average  times  of  eruption  of  the  Tem- 
porary and  Permanent  teeth.  In  both  cases,  the  eruption  of  any  given 
tooth  of  the  lower  jaw  precedes,  as  a  rule,  that  of  the  corresponding 
tooth  of  the  upper. 

Temporary  or  Milk   Teeth. 
The  figures  indicate  in  months  the  age  at  which  each  tooth  appears. 


Deciduous 

Molars. 

Canines. 

Incisors. 

Canines. 

Deciduous 
Molars. 

24     12 

18 

9  7  7  9 

18 

12     24 

DIGESTION. 


223 


Permanent  Teeth. 
The  age  at  which  each  tooth  is  cut  is  indicated  in  this  table  in  years. 


Biscupid  or 
Molars.     Premolars.    Canines. 


Incisors. 


Biscupid  or 
(  aiiines.  Premolars.      Molars. 


17 

12 

1 

1 

12 

17 

to 

to  6 

10  9 

11  to  12  j  8  7  7  8 

11  to  12 

9  10  | 

6  to 

to 

25 

13 

13 

25 

.  The  times  of  eruption  given  in  the  above  tables  are  only  approximate, 
the  limits  of  variation  being  tolerably  wide.  Some  children  may  cut 
their  first  teeth  before  the  age  of  six  months,  and  others  not  till  nearly 
the  twelfth  month.  In  nearly  all  cases  the  two  central  incisors  of  the 
lower  jaw  are  cut  first ;  these  being  succeeded  after  a  short  interval  by 
the  four  incisors  of  the  upper  jaw,  next  follow  the  lateral  incisors  of  the 
lower  jaw,  and  so  on  as  indicated  in  the  table  till  the  completion  of  the 
milk  dentition  at  about  the  age  of  two  years. 

The  milk-teeth  usually  come  through  in  batches,  each  period  of 
eruption  being  succeeded  by  one  of  quiescence  lasting  sometimes  several 
months.  The  milk-teeth  are  in  use  from  the  age  of  two  up  to  five  and 
a  half  years;  at  about  this  age  the  first  permanent  molars  (four  in  num- 
ber) make  their  appearance  behind  the  milk-molars,  and  for  a  short 
time  the  child  has  four  permanent  and  twenty  temporary  teeth  in  posi- 
tion at  once. 

It  is  worthy  of  note  that  from  the  age  of  five  years  to  the  shedding 
of  the  first  milk-tooth  the  child  has  no  fewer  than  forty-eight  teeth, 
twenty  milk  teeth  and  twenty-eight  calcified  germs  of  permanent  teeth 
(all  in  fact  except  the  four  wisdom  teeth). 


Structure  of  a  Tooth. 

A  tooth  is  generally  described  as  possessing  a  crown,  neck,  and  fang 
or  fangs. 

The  crown  is  the  portion  which  projects  beyond  the  level  of  the  gum. 
The  neck  is  that  constricted  portion  just  below  the  crown  which  is  em- 
braced by  the  free  edges  of  the  gum,  and  the  fang  includes  all  below 
this. 

On  making  a  longitudinal  section  through  its  centre  (Figs.  166, 
167),  a  tooth  is  found  to  be  principally  composed  of  a  hard  material, 
dentine  or  ivory,  which  is  hollowed  out  into  a  central  cavity  which 
resembles  in  general  shape  the  outline  of  the  tooth,  and  is  called  the 
pulp  cavity,  from  its  containing  the  very  vascular  and  sensitive  tooth 
pulp  which  is  composed  of  connective  tissue,  blood-vessels,  and  nerves. 

The  blood-vessels  and  nerves  enter  the  pulp  through  a  small  opening 
at  the  extremity  of  the  fang. 


2U 


HANDBOOK    OF    PHYSIOLOGY. 


A  layer  of  very  hard  calcareous  matter,  the  enamel,  caps  that  part  of 
the  dentine  which  projects  beyond  the  level  of  the  gum  ;  while  sheath- 
ing the  portion  of  dentine  which  is  beneath  the  level  of  the  gum,  is  a, 
layer  of  true  bone,  called  the  cement  or  crusta  petrosa. 


Fig.  166.— a.  Longitudinal  section  of  a  human  molar  tooth:  c,  cement;  d,  dentine;  e,  enamel;  v, 
pulp  cavity.    (Owen.) 

B.  Transverse  section.    The  letters  indicate  the  same  as  in  a. 

At  the  neck  of  the  tooth,  where  the  enamel  and  cement  come  into 
contact,  each  is  reduced  to  an  exceedingly  thin  layer.  The  covering  of 
enamel  becomes  thicker  towards  the  crown,  and  the  cement  towards  the 
lower  end  or  apex  of  the  fang. 


I. — Dentine. 

Chemical  composition. — Dentine  closely  resembles  bone  in  chemical 
composition.  It  contains,  however,  rather  less  animal  matter;  the  pro- 
portion in  a  hundred  parts  being  about  twenty-eight  animal  to  seventy- 
two  of  earthy.  The  former,  like  the  animal  matter  of  bone,  may  be  re- 
solved into  gelatin  by  boiling.  The  earthy  matter  is  made  up  chiefly  of 
calcium  phosphate,  with  a  small  portion  of  the  carbonate,  and  traces  of 
calcium  fluoride  and  magnesium  phosphate. 

Structure. — Under  the  microscope  dentine  is  seen  to  be  finely  chan- 
nelled by  a  multitude  of  delicate  tubes,  which,  by  their  inner  ends, 
communicate  with  the  pulp-cavity;  and  by  their  outer  extremities  come 
into  contact  with  the  under  part  of  the  enamel  and  cement,  and  some- 
times even  penetrate  them  for  a  greater  or  less  distance  (Fig.  168). 

In  their  course  from  the  pulp-cavity  to  the  surface,  the  minute  tubes 
form  gentle  and  nearly  parallel  curves  and  divide  and  subdivide  dicho- 
tomously,  but  without  much  lessening  of  their  calibre  until  they  are  ap- 
proaching their  peripheral  termination. 

From  their  sides  proceed  other  exceedingly  minute  secondary  canals, 


DIGESTION. 


225 


which  extend  into  the  dentine  between  the  tubules,  and  anastomose  with 
each  other.  The  tubules  of  the  dentine,  the  average  diameter  of  which 
at  their  inner  and  larger  extremity  is  43V0  0*  an  inch,;  contain  fine  pro- 
longations from  the  tooth-pulp,  which 
give  the  dentine  a  certain  faint  sensitive- 
ness under  ordinary  circumstances  and, 
without  doubt,  have  to  do  also  with  its 
nutrition.  These  prolongations  from  the 
tooth-pulp  are  really  processes  of  the  den- 
tine-cells or  odontoblasts,  which  are 
branched  cells  lining  the  pulp-cavity  ;  the 
relation  of  these  processes  to  the  tubules 
in  which  they  lie  being  precisely  similar 
to  that  of  the  processes  of  the  bone-cor- 
puscles to  the  canaliculi  of  bone.  The 
outer  portion  of  the  dentine,  underlying 
both  the  cement  and  enamel,  forms  a 
more  or  less  distinct  layer  termed  the 
granular  or  interglobular  layer.  It  is 
characterized  by  the  presence  of  a  number 
of  minute  cell-like  cavities,  much  more 
closely  packed  than  the  lacunae  in  the 
cement,  and  communicating  with  one  an- 
other and  with  the  ends  of  the  dentine- 
tubes  (Fig.  1G8),  and  containing  cells  like 
bone-corpuscles. 


II. — Enamel. 
Chemical   composition.  — The 


Fig.  167.— Premolar  tooth  of  cat  in 
situ.  Vertical  section.  1.  Enamel  with 
decussating  and  parallel  strife.  2.  Den- 
tine with  Scbreger's  lines.  3.  Cement. 
4.  Periosteum  of  the  alveolus.  5.  In- 
ferior maxillary  bone,  showing  canal 
for  the  inferior  dental  nerve  and  ves- 
sels, which  appears  nearly  circular 
in  transverse  section.    (Waldeyer.) 


enamel, 
which  is  by  far  the  hardest  portion  of  a 
tooth,  is  composed,  chemically,  of  the  same  elements  that  enter  into  the 
composition  of  dentine  and  bone.     Its  animal  matter,  however,  amounts 


Fig.  168.— Section  of  a  portion  of  the  dentine  and  cement  from  the  middle  of  the  root  of  an  incisor 
tooth,  a,  dental  tubuli  ramifying  and  terminating,  some  of  them  in  the  interglobular  spaces  b  and 
c,  which  somewhat  resemble  bone  lacuna1;  rf,  inner  layer  of  the  cement  with  numerous  closely  set 
canaliculi;  e,  outer  layer  of  cement;  /,  lacuna?;  </,  canaliculi.    x  350.    (Kolliker.) 

15 


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HANDBOOK   OF    PHYSIOLOGY. 


only  to  about  2  or  3  per  cent.     It  contains  a  larger  proportion  of  inor- 
ganic matter  and  is  harder  than  any  other  tissue  in  the  body. 

Structure. — Examined  under  the  microscope,  enamel  is  found  com- 
posed of  fine  hexagonal  fibres  (Figs.  169,  170) 
joVtt  of  an  inch  in  diameter,  which  are  set  on 
end  on  the  surface  of  the  dentine,  and  fit  into 
corresponding  depressions  in  the  same. 

They  radiate  in  such  a  manner  from  the  den- 
tine that  at  the  top  of  the  tooth  they  are  more  or 
less  vertical,  while  towards  the  sides  they  tend  to 
the  horizontal  direction.  Like  the  dentine  tu- 
bules, they  are  not  straight,  but  disposed  in  wavy 
and  parallel  curves.  The  fibres  are  marked  by 
transverse  lines,  and  are  mostly  solid,  but  some  of 
them  contain  a  very  minute  canal. 

The  enamel-prisms  are  connected  together  by 
a  very  minute  quantity  of  hyaline  cement-sub- 
stance. In  the  deeper  part  of  the  enamel,  between 
the  prisms,  are  small  lacunce,  which  communicate 
with  the  "  interglobular  spaces  "  on  the  surface  of 
the  dentine. 

The  enamel  itself  is  coated  on  the  outside  by 
a  very  thin  calcified  membrane,  sometimes  termed 
the  cuticle  of  the  enamel. 


Fig.  169. -Thin  section 
of  the  enamel  and  a  part  of 
the  dentine,  a,  cuticular 
pellicle  of  the  enamel;  b, 
enamel  fibres,  or  columns 
with  fissures  between  them 
and  cross  striae;  c,  larger 
cavities  in  the  enamel,  com- 
municating with  the  extrem- 
ities of  some  of  the  tubuli 
(d).     X  350.    (Kolliker.) 


III. — Crusta  Petrosa. 


The  crusta  petrosa,  or  cement  (Fig.  168,  c,  d), 
is  composed  of  true  bone,  and  in  it  are  lacuna? 
(/*)  and  canaliculi  (g),  which  sometimes  com- 
municate with  the  outer  finely  branched  ends  of 
the  dentine  tubules.  Its  laminae  are  as  it  were 
bolted  together  by  perforating  fibres  like  those  of  ordinary  bone,  but  it 
differs  from  ordinary  bone  in  possessing  Haversian  canals  only  in  the 
thickest  part. 

Development  of  the  Teeth. 

Development  of  the  Teeth. — The  first  step  in  the  development  of  the 
teeth  consists  in  a  downward  growth  (Fig.  171,  a,  1)  from  the  stratified 
epithelium  of  the  mucous  membrane  of  the  mouth,  which  first  becomes 
thickened  in  the  neighborhood  of  the  jaws  or  maxillae  which  are  in  the 
course  of  formation.  This  process  passes  downward  into  a  recess  (enamel 
groove)  of  the  imperfectly  developed  tissue  of  the  embryonic  jaw.  The 
downward  epithelial  growth  forms  the  primary  enamel  organ  or  enamel 
germ,  and  its   position  is  indicated  by  a  slight  groove  in  the  mucous 


DIGKSTION. 


22  7 


membrane  of  the  jaw.  The  next  step  in  the  process  consists  in  the 
elongation  downward  of  the  enamel  groove  and  of  the  enamel  germ  and 
the  inclination  outward  of  the  deeper  part  (Fig.  171,  b,  /'),  which  is  now 
inclined  at  an  angle  with  the  upper  portion  or  neck  (/),  and  has  become 
bulbous.  After  this,  there  is  an  increased  development  at  certain  points 
corresponding  to  the  situations  of  the  future  milk-teeth,  and  the  enamel 
germ  or  common  enamel  germ,  as  it  may  be  called,  becomes  divided  at 
its  deeper  portion,  or  extended  by  further  growth,  into  a  number  of 
special  enamel  germs  corresponding  to  each  of  the  above-mentioned  milk- 
teeth,  and  connected  to  the  common  germ  by  a  narrow  neck,  each  tooth 
being  placed  in  its  own  special  recess  in  the  embryonic  jaw  (Fig.  171,  b, 

As  these  changes  proceed,  there  grows  up  from  the  underlying  tissue 
into  each  enamel  germ  (Fig.  171,  c,  p),  a  distinct  vascular  papilla  (den- 


Fig.  170.—  Enamel  fibres.  A,  fragments  and  single  fibres  of  the  enamel,  isolated  by  the  action 
of  hydrochloric  acid.  B,  surface  of  a  small  fragment  of  enamel,  showing  the  hexagonal  ends  of 
the  fibres.     X  350.    (Kolliker. 

tal  papilla),  and  upon  it  the  enamel  germ  becomes  moulded,  and  pre- 
sents the  appearance  of  a  cap  of  two  layers  of  epithelium  separated  by  an 
interval  (Fig.  171,  c,  /').  Whilst  part  of  the  sub-epithelial  tissue  is  ele- 
vated to  form  the  dental  papilla?,  the  part  which  bounds  the  embryonic 
teeth  forms  the  dental  sacs  (Fig.  171,  c,  s)  ;  and  the  rudiment  of  the 
jaw,  at  first  a  bony  gutter  in  which  the  teeth  germs  lie,  sends  up  processes 
forming  partitions  between  the  teeth.  In  this  way  small  chambers  are 
produced  in  which  the  dental  sacs  are  contained,  and  thus  the  sockets  of 
the  teeth  are  formed.  The  papilla,  which  is  really  part  of  the  dental  sac 
(if  one  thinks  of  this  as  the  whole  of  the  sub-epithelial  tissue  surround- 
ing the  enamel  organ  and  interposed  between  the  enamel  germ  and  the 
developing  bony  jaw),  is  composed  of  nucleated  cells  arranged  in  a  mesh- 
work,  the  outer  or  peripheral  j>art  being  covered  with  a  layer  of  colum- 


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HANDBOOK    OF    PHYSIOLOGY. 


nar  nucleated  cells  called  odontoblasts.  The  odontoblasts  form  the  den- 
tine, while  the  remainder  of  the  papilla  forms  the  tooth-pulp.  The 
method  of  the  formation  of  the  dentine  from  the  odontoblasts  is  as 
follows  : — The  cells  elongate  at  their  outer  part*  and  these  processes  are 
directly  converted  into  the  tubules  of  dentine  (Fig.  172).     The  continued 

formation  of  dentine  proceeds 


by  the  elongation  of  the  odon- 
toblasts, and  their  subsequent 
conversion  by  a  process  of  cal- 
cification into  dentine  tubules. 
The  most  recently  formed  tu- 
bules are  not  immediately  cal- 
cified. The  dentine  fibres  con- 
tained in  the  tubules  are  said 
to  be  formed  from  processes  of 
the  deeper  layer  of  odonto- 
blasts, which  are  wedged  in  be- 
tween the  cells  of  the  super- 
ficial layer  (Fig.  172)  which 
form  the  tubules  only. 

Since  the  papillae  are  to 
form  the  main  portion  of  each 
tooth,  i.e.,  the  dentine,  each 
of  them  early  takes  the  shape 
of  the  crown  of  the  tooth  to 
which  it  corresponds.  As  the 
dentine  increases  in  thickness, 
the  papilla?  diminish,  and  at 
last  when  the  tooth  is  cut,  only 
a  small  amount  of  the  papilla 
remains  as  the  dental  pulp, 
and  is  supplied  by  vessels  and 
nerves  which  enter  at  the  end 
of  the  fang.  The  shape  of  the 
crown  of  the  tooth  is  taken  by 
the  corresponding  papilla,  and 
that  of  the  single  or  double 
fang  by  the  subsequent  con- 
striction below  the  crown,  or  by  division  of  the  lower  part  of  the  papilla. 
The  enamel  cap  is  found  later  on  to  consist  (Fig.  173)  of  three  parts; 
(a)  an  inner  membrane,  composed  of  a  layer  of  columnar  epithelium  in 
contact  with  the  dentine,  called  enamel  cells,  and  outside  of  these  one  or 
more  layers  of  small  polyhedral  nucleated  cells  (stratum  intermedium  of 
Hannover);  (b)  an  outer  membrane  of  several  layers  of  epithelium;  (c) 


Fig.  171.— Section  of  the  upper  jaw  of  a  f  oetal 
sheep.  A. — 1,  common  enamel  germ  dipping  down 
into  the  mucous  membrane;  2,  palatine  process 
of  jaw.  B.— Section  similar  to  A,  but  passing 
through  one  of  the  special  enamel-germs  here  be- 
coming flask-shaped;  c,  c',  epithelium  of  mouth;  /, 
neck;  /',  body  of  special  enamel  germ.  C— A  later 
stage;  c,  outline  of  epithelium  of  gum ;  /,  neck  of 
enamel  germ;/',  enamel  organ;  p,  papilla;  s,  dental 
sac  forming;  fp,  the  enamel  germ  of  peraianent 
tooth.  rWaldeyer  and  KOllikerj  Copied  from 
Quain's  Anatomy. 


DIGESTION. 


22.9 


a  mirldle  membrane  formed  of  a  matrix  of  non-vascular  gelatinous  tissue 
containing  a  hyaline  interstitial  substance.  The  enamel  is  formed  by 
the  enamel  cells  of  the  inner  membrane,  by  the  elongation  of  their  distal 


Fig.  172.— Part  of  section  of  developing  tooth  of  a  young  rat,  showing  the  mode  of  desposition 
of  the  dentine.  Highly  magnified,  a,  outer  laver  of  fully  formed  dentine;  6,  uncalcifled  matrix 
with  one  or  two  nodules  of  calcareous  matter  near  the  calcified  parts;  c,  odontoblasts  sending  pro- 
cesses into  the  dentine;  d,  pulp.  The  section  is  stained  in  carmine,  which  colors  the  uncalcifled 
matrix  but  not  the  calcified  part.    (E.  A.  Schaf  er ,) 

extremities,  and  the  direct  conversion  of  these  processes  into  enamel. 

The  calcification  of  the  enamel  processes  or  prisms  takes  place  first  at  the 

periphery,  the  centre  remaining  for 

a  time  transparent.     The  cells  of 

the  stratum  intermedium  are  used 

for  the  regeneration  of  the  enamel 

cells,    but    these   and   the   middle 

membrane  after  a  time  disappear. 

The  cells  of   the  outer  membrane 

give  origin  to   the   cuticle  of   the 

enamel. 

The  cement  or  crusta  petrosa  is 
formed  from  the  tissue  of  the  tooth 
sac,  the  structure  and  function  of 
which  are  identical  with  those  of 
the  osteogenetic  layer  of  the  perios- 
teum. 

In  this  manner  the  first  set  of 
teeth,  or  the  milk-teeth,  are  formed; 
and  each  tooth,  by  degrees  develop- 
ing, presses  at  length  on  the  wall 
of  the  sac  inclosing  it,  and,  caus- 
ing its  absorption,  is  cut,  to  use  a 
familiar  phrase. 

The    temporary   or    milk-teeth, 
are  speedily  replaced  by  the  growth 
•of  the  permanent  teeth,  which  push  their  way  up  from  beneath  them,  ab- 
sorbing in  their  progress  the  whole  of  the  fang  of  each  milk-tooth,  and 


Fig.  173.— Vertical  transverse  section  of  the 
dentalsac,  pulp,  etc.,  of  a  kitten,  a,  dental  pa- 
pilla or  pulp;  o,  the  cap  of  dentine  formed  upon 
the  summit;  c,  its  covering  of  enamel;  d, 
inner  layer  of  epithelium  of  the  enamel  organ : 
e,  gelatinous  tissue;  /,  outer  epithelial  layer  of 
the  enamel  organ;  c?,  inner  layer,  and  h,  outer 
layer  of  dentalsac.    x  14.    ^Thiersch.) 


230  HANDBOOK    OF   PHYSIOLOGY. 

leaving  at  length  only  the  crown  as  a  mere  shell,  which  is  shed  to  make 
way  for  the  eruption  of  the  permanent  teeth  (Fig.  165). 

Each  temporary  tooth  is  replaced  by  a  corresponding  tooth  of  the 
permanent  set  which  is  developed  from  a  small  sac  set  by,  so  to  speak, 
from  the  sac  of  the  temporary  tooth  which  precedes  it,  and  called  the 
cavity  of  reserve. 

Mastication. 

The  act  of  chewing  or  mastication  is  performed  by  the  biting  and 
grinding  movement  of  the  lower  range  of  teeth  against  the  upper.  The 
simultaneous  movements  of  the  tongue  and  cheeks  assist  partly  by  crush- 
ing the  softer  portions  of  the  food  against  the  hard  palate  and  gums,  and 
thus  supplementing  the  action  of  the  teeth,  and  partly  by  returning  the 
morsels  of  food  to  the  action  of  the  teeth,  again  and  again,  as  they  are 
squeezed  out  from  between  them,  until  they  have  been  sufficiently 
chewed. 

Muscles. — The  simple  up  and  down,  or  biting  movements  of  the  lower 
jaw,  are  performed  by  the  temporal,  masseter,  and  internal  pterygoid 
muscles,  the  action  of  which  in  closing  the  jaws  alternates  with  that  of 
the  digastric  and  other  muscles  passing  from  the  os  hyoides  to  the  lower 
jaw,  which  open  them.  The  grinding  or  side  to  side  movements  of  the 
lower  jaw  are  performed  mainly  by  the  external  pterygoid  muscles,  the 
muscle  of  one  side  acting  alternately  with  the  other.  When  both  exter- 
nal pterygoids  act  together,  the  lower  jaw  is  pulled  directly  forwards,  so 
that  the  lower  incisor  teeth  are  brought  in  front  of  the  level  of  the  upper. 

Temporo-maxillary  Fibro-cartilage. — The  function  of  the  inter-artic- 
ular fibro-cartilage  of  the  temporo-maxillary  joint  in  mastication  is  to 
serve  :  (1)  As  an  elastic  pad  to  distribute  the  pressure  caused  by  the  ex- 
ceedingly powerful  action  of  the  masticatory  muscles.  (2)  As  a  joint- 
surface  or  socket  for  the  condyle  of  the  lower  jaw,  when  the  latter  has 
been  partially  drawn  forward  out  of  the  glenoid  cavity  of  the  temporal 
bone  by  the  external  pterygoid  muscle,  some  of  the  fibres  of  the  latter 
being  attached  to  its  front  surface,  and  consequently  drawing  it  forward 
with  the  condyle  which  moves  on  it. 

Nervous  Mechanism. — The  act  of  mastication  is  partly  voluntary  and 
partly  reflex  and  involuntary.  The  consideration  of  such  sensori-motor 
actions  will  come  hereafter  (see  Chapter  on  the  Nervous  System).  It 
will  suffice  here  to  state  that  the  afferent  nerves  chiefly  concerned  are 
the  sensory  branches  of  the  fifth  and  the  glosso-pharyngeal,  and  the  ef- 
ferent are  the  motor  branches  of  the  fifth  and  the  ninth  (hypoglossal) 
cerebral  nerves.  The  nerve-centre  through  which  the  reflex  action  oc- 
curs, and  by  which  the  movements  of  the  various  muscles  are  harmo- 
nized, is  situated  in  the  medulla  oblongata.  In  so  far  as  mastication  is 
voluntary  or  mentally  perceived,  it  becomes  so  under  the  influence,  in 
addition  to  the  medulla  oblongata,  of  the  cerebral  hemispheres. 


digkstion.  231 

Insalivation. 

The  act  of  mastication  is  much  assisted  by  the  saliva  which  is  secreted 
by  the  salivary  glands  in  largely  increased  amount  during  the  process, 
and  the  intimate  incorporation  of  which  with  the  food,  as  it  is  being 
chewed,  is  termed  insalivation. 

The  Salivary  Glands. 

The  human  salivary  glands  are  the  parotid,  the  submaxillary ,  and 
the  sublingual,  and  numerous  smaller  bodies  of  similar  structure,  and 
with  separate  ducts,  which  are  scattered  thickly  beneath  the  mucous 
membrane  of  the  lips,  cheeks,  soft  palate,  and  root  of  the  tongue. 

Structure. — The  salivary  glands  are  compound  tubular  glands.  They 
are  made  up  of  lobules.     Each  lobule  consists  of  the  branchings  of  a 


Fig.  174.— Section  of  submaxillary  gland  of  dog.    Showing  gland  cells,  ft,  and  a  duct,  a,  in  sec- 
tion.   (Kolliker.) 

subdivision  of  the  main  duct  of  the  gland,  which  are  generally  more  or 
less  convoluted  towards  their  extremities,  and  sometimes,  according  to 
some  observers,  sacculated  or  pouched.  The  convoluted  or  pouched 
portions  form  the  alveoli,  or  proper  secreting  parts  of  the  gland.  The 
alveoli  are  composed  of  a  basement  membrane  of  flattened  cells  joined 
together  by  processes  to  produce  a  fenestrated  membrane,  the  spaces  of 
which  are  occupied  by  a  homogeneous  ground-substance.  Within,  upon 
this  membrane,  which  forms  the  tube,  the  nucleated  salivary  secreting 
cells,  of  cubical  or  columnar  form,  are  arranged  parallel  to  one  another 
inclosing  a  central  canal.  The  granular  appearance  frequently  seen  in 
the  salivary  cells  is  due  to  the  very  dense  network  of  fibrils  which  they 
contain.  When  isolated,  the  cells  not  uufrequently  are  found  to  be 
branched.  Connecting  the  alveoli  into  lobules  is  a  considerable  amount 
of  fibrous  connective  tissue,  which  contains  both  flattened  and  granular 
protoplasmic  cells,  lymph  corpuscles,  and  in  some  cases  fat  cells.  The 
lobules  are  connected  to  form  larger  lobules  (lobes),  in  a  similar  man- 
ner.    The  alveoli  pass  into  the  intralobular  ducts  by  a  narrowed  portion 


232 


HANDBOOK    OF   PHYSIOLOGY. 


(intercalary),  lined  with  flattened  epithelium  with  elongated  nuclei. 
The  intercalary  ducts  pass  into  the  intralobular  ducts  by  a  narrowed 
neck,  lined  with  cubical  cells  with  small  nuclei.  The  intralobular  duct 
is  larger  in  size,  and  is  lined  with  large  columnar  nucleated  cells,  the 
parts  of  which,  towards  the  lumen  of  the  tube,  present  a  fine  longitudi- 
nal striation,  due  to  the  arrangement  of  the  cell  network.  It  is  most 
marked  in  the  submaxillary  gland.  The  intralobular  ducts  pass  into 
the  larger  ducts,  and  these  into  the  main  duct  of  the  gland.  As  these 
ducts  become  larger  they  acquire  an  outside  coating  of  connective  tissue, 
and  later  on  some  unstriped  muscular  fibres.  The  lining  of  the  larger 
ducts  consist  of  one  or  more  layers  of  columnar  epithelium,  the  cells  of 
which  contain  an  intracellular  network  of  fibres  arranged  longitudinally. 
Varieties.  —  Certain  differences  in  the  structure  of  salivary  glands 


Fig.  175. 


Fig.  176. 


Fig.  175. — From  a  section  through  a  true  salivary  gland,  a,  the  gland  alveoli,  lined  with  albu- 
minous "  salivary  cells;"  b,  intralobular  duct  cut  transversely.    (Klein  and  Nob  e  Smith.) 

Fig.  176.— From  a  section  through  a  mucous  gland  in  a  quiescent  state.  The  alveoli  are  lined 
with  transparent  mucous  cells,  and  outside  these  are  the  semilunes  of  Heidenhain.  The  cells  should 
have  been  represented  as  more  or  less  granular.    (Heidenhain.) 

may  be  observed  according  as  the  glands  secrete  pure  saliva,  or  saliva 
mixed  with  mucus,  or  pure  mucus,  and  therefore  the  glands  have  been 
classified  as  : — 

(1)  True  salivary  glands  (called  most  unfortunately  by  some  serous 
glands),  e.  g.,  the  parotid  of  man  and  other  animals,  and  the  submaxil- 
lary of  the  rabbit  and  the  guinea-pig  (Fig.  175).  In  this  kind  the  alve- 
olar lumen  is  small,  and  the  cells  lining  the  tubule  are  short  granular 
columnar  cells,  with  nuclei  presenting  the  intranuclear  network.  Dur- 
ing rest  the  cells  become  larger,  highly  granular,  with  obscured  nuclei, 
and  the  lumen  becomes  smaller.  During  activity,  and  after  stimulation 
of  the  sympathetic,  the  cells  become  smaller  and  their  contents  more 
opaque  ;  the  granules  first  of  all  disappearing  from  the  outer  part  of  the 
cells,  and  then  being  found  only  at  the  extreme  inner  part  and  contigu- 
ous border  of  the  cell.     The  nuclei  reappear,  as  does  also  the  lumen. 

(2)  In  the  true  mucous-secreting  glands,  as  the  sublingual  of  man  and 


DIGESTION. 


233 


other  animals,  and  in  the  submaxillary  of  the  dog,  the  tubes  are  larger, 
contain  a  larger  lumen  and  also  have  larger  cells  lining  them.  The  cells 
are  of  two  kinds,  (a)  mucous  or  central  cells,  which  are  transparent  col- 
umnar cells  with  nuclei  near  the  basement  membrane.  The  cell  sub- 
stance is  made  up  of  a  fine  network,  which  in  the  resting  state  contains 
a  transparent  substance  called  mucigen,  during  which  the  cell  does  not 
stain  well  with  logwood  (Fig.  176).  When  the  gland  is  secreting,  mu- 
cigen is  converted  into  mucin,  and  the  cells  swell  up,  appear  more  trans- 
parent and  stain  deeply  in  logwood  (Fig.  177).  During  rest,  the  cells 
become  smaller  and  more  granular  from  having  discharged  their  con- 
tents. The  nuclei  appear  more  distinct,  (b)  Semilunes  of  Heidenhain 
(Fig.  176),  which  are  crescentic  masses  of  granular  parietal  cells  fouud 
here  and  there  between  the  basement  membrane  and  the  central  cells. 
The  cells  composing  the  mass  are  small  and  have  a  very  dense  reticulum, 
the  nuclei  are  spherical,  and  increase 
in  size  during  secretion.  In  the  mu- 
cous gland  there  are  some  large  tubes, 
lined  with  large  transparent  central 
cells,  and  having  besides  a  few  granu- 
lar parietal  cells  ;  other  small  tubes 
are  lined  with  small  granular  parietal 
cells  alone  ;  and  a  third  variety  are 
lined  equally  with  each  kind  of  cell. 

(3)  In  the  muco-salivary  or  mixed 
glands,  as  the  human  submaxillary 
gland,  part  of  the  gland  presents  the 
structure  of  the  mucous  gland  whilst 
the  remainder  has  that  of  the  salivary  glands  proper. 

Nerves  and  Blood-vessels. — Nerves  of  large  size  are  found  in  the  sali- 
vary glands,  they  are  principally  contained  in  the  connective  tissue  of 
the  alveoli,  and  in  certain  glands,  especially  in  the  dog,  are  provided 
with  ganglia.  Some  nerves  have  special  endings  in  Pacinian  corpuscles, 
some  supply  the  blood-vessels,  and  others,  according  to  Pfliiger,  pene- 
trate the  basement  membrane  of  the  alveoli  and  enter  the  salivary  cells. 

The  blood-vessels  form  a  dense  capillary  network  around  the  ducts 
of  the  alveoli,  being  carried  in  by  the  fibrous  trabecule  between  the  al- 
veoli, in  which  also  begin  the  lymphatics  by  lacunar  spaces. 


Fig.  177.— A  part  of  a  section  through 
a  mucous  gland  after  prolonged  electrical 
stimulation.  The  alveoli  are  lined  with 
small  granular  cells.    (Lavdovski.) 


Saliva. 

Saliva,  as  it  commonly  flows  from  the  mouth,  is  mixed  with  the 
secretion  of  the  mucous  glands,  and  often  with  air  bubble,  which,  being 
retained  by  its  viscidity,  make  it  frothy.  When  obtained  from  the 
parotid  ducts,  and  free  from  mucus,  saliva  is  a  transparent  watery  fluid, 
the  specific  gravity  of  which  varies  from  1004  to  1008,  and  in  which, 


234  HANDBOOK    OF   PHYSIOLOGY. 

when  examined  with  the  microscope,  are  found  floating  a  number  of  mi- 
nute particles,  derived  from  the  secreting  ducts  and  vesicles  of  the  glands. 
In  the  impure  or  mixed  saliva  are  found,  besides  these  particles,  numer- 
ous epithelial  scales  separated  from  the  surface  of  the  mucous  mem- 
brane of  the  mouth  and  tongue,  and  the  so-called  salivary  corpuscles,, 
discharged  probably  from  the  mucous  glands  of  the  mouth  and  the  ton- 
sils, which,  when  the  saliva  is  collected  in  a  deep  vessel,  and  left  at  rest, 
subside  in  the  form  of  a  white  opaque  matter,  leaving  the  supernatant 
salivary  fluid  transparent  and  colorless,  or  with  a  pale  bluish-gray  tint. 
In  reaction,  the  saliva,  when  first  secreted,  appears  to  be  always  alka- 
line. During  fasting,  the  saliva,  although  secreted  alkaline,  shortly  be- 
comes neutral;  especially  when  it  is  secreted  slowly  and  is  allowed  to  mix 
with  the  acid  mucus  of  the  mouth,  by  which  its  alkaline  reaction  is 
neutralized. 

Chemical  Composition   of  Mixed  Saliva  (Frerichs). 

Water, 994.10 

Solids  :— 

Ptyalin,       .         '.         .         .         .  1.41 

Fat, 0.07 

Epithelium  and  Proteids  (including 
Serum-Albumin,  Globulin,  Mucin, 
etc.),         .....         2.13 

Salts  : — 

Potassium  Sulpho-Cyanate,      .       .    ") 

Sodium  Phosphate,  .         .  | 

Calcium  Phosphate.      .         .  •    l  2  2Q 

Magnesium  Phosphate,      .  ( 

Sodium  Chloride,  .  .     | 

Potassium  Chloride,  .         .         .     .    J 

5.9 


1000 


The  presence  of  potassium  sulphocyanate  (or  thiocyanate)  (C  N  K  S) 
in  saliva,  may  be  shown  by  the  blood-red  coloration  which  the  fluid 
gives  with  a  solution  of  ferric  chloride  (Fe.2  C1.6),  and  which  is  bleached 
on  the  addition  of  a  solution  of  mercuric  chloride  (Hg  Gl  J,  but  not  by 
hydrochloric  acid. 

Rate  of  Secretion  and  Quantity. — The  rate  at  which  saliva  is  secreted 
is  subject  to  considerable  variation.  When  the  tongue  and  muscles  con- 
cerned in  mastication  are  at  rest,  and  the  nerves  of  the  mouth  are  sub- 
ject to  no  unusual  stimulus,  the  quantity  secreted  is  not  more  than 
sufficient,  with  the  mucus,  to  keep  the  mouth  moist.  During  actual 
secretion  the  flow  is  much  accelerated. 

The  quantity  secreted  in  twenty-four  hours  varies  :  its  average, 
amount  is  probably  from  1  to  3  pints  (1  to  2  litres). 


DIGESTION.  235 

Uses  of  Saliva. — The  purposes  served  by  saliva  are  (1)  mechanical  and 
(2)  chemical. 

I.  Mechanical. — (1)  It  keeps  the  mouth  in  a  due  condition  of  mois- 
ture, facilitating  the  movements  of  the  tongue  in  speaking,  and  the 
mastication  of  food.  (2)  It  serves  also  in  dissolving  sapid  substances, 
and  rendering  them  capable  of  exciting  the  nerves  of  taste.  But  the 
principal  mechanical  purpose  of  the  saliva  is,  (3)  that  by  mixing  with 
the  food  during  mastication,  it  makes  it  a  soft  pulpy  mass,  such  as  may 
be  easily  swallowed.  To  this  purpose  the  saliva  is  adapted  both  by 
quantity  and  quality.  For,  speaking  generally,  the  quantity  secreted 
during  feeding  is  in  direct  proportion  to  the  dryness  and  hardness  of  the 
food.  The  quality  of  saliva  is  equally  adapted  to  this  end.  It  is  easy  to 
see  how  much  more  readily  it  mixes  with  most  kind  of  foods  than  water 
alone  does  ;  and  the  saliva  from  the  parotid,  labial,  and  other  small 
glands,  being  more  aqueous  than  the  rest,  is  that  which  is  chiefly 
braided  and  mixed  with  the  food  in  mastication  ;  while  the  more  viscid 
mucous  secretion  of  the  submaxillary,  palatine,  and  tonsillitic  glands 
is  spread  over  the  surface  of  the  softened  mass,  to  enable  it  to  slide  more 
easily  through  the  fauces  and  oesophagus. 

II.  Chemical. — The  chemical  action  which  the  saliva  exerts  upon  the 
food  in  the  mouth  is  to  convert  the  starchy  materials  which  it  contains 
into  some  kind  of  sugar.  This  power  the  saliva  owes  to  one  of  its  con- 
stituents ptyalin,  which  is  a  nitrogenous  body  of  uncertain  composition. 
It  is  classed  among  the  unorganized  ferments,  which  are  substances  of 
uncertain  composition  capable  of  producing  changes  in  the  composition 
of  other  bodies  with  which  they  come  into  contact,  without  themselves 
undergoing  change  of  suffering  diminution.  The  conversion  of  the 
starcli  under  the  influence  of  the  ferment  into  sugar  takes  place  in  sev- 
eral stages,  and  in  order  to  understand  it,  a  knowledge  of  the  structure 
and  composition  of  starch  granules  is  necessary.  A  starch  granule  con- 
sists of  two  parts  :  an  envelope  of  cellulose,  which  does  not  give  a  blue 
color  with  iodine  except  on  addition  of  sulphuric  acid,  and  of  granulosa, 
which  is  contained  within,  and  which  gives  a  blue  with  iodine  alone. 
Briike  states  that  a  third  body  is  contained  in  the  granule,  which  gives 
a  red  with  iodine,  viz.,  erythro-granulose.  On  boiling,  the  granulose 
swells  up,  bursts  the  envelope,  and  the  whole  granule  is  more  or  less  com- 
pletely converted  into  a  paste  or  gruel,  which  is  called  gelatinous  starcli. 

"When  ptyalin  or  other  amylolytic  ferment  is  added  to  boiled  starch, 
sugar  almost  at  once  makes  its  appearance  in  small  quantities,  but  in  ad- 
dition there  is  another  body,  intermediate  between  starcli  and  sugar, 
called  erythro-dextrin,  which  gives  a  reddish-brown  coloration  with 
iodine.  As  the  sugar  increases  in  amount,  the  erythro-dextrin  disappears, 
but  its  place  is  taken  in  part  by  another  dextrin,  achroo-dextrin,  which 


'236  HANDBOOK    OF    PHYSIOLOGY. 

gives  no  color  with  iodine.     However  long  the  reaction  goes  on,  it  is  un- 
likely that  all  the  dextrin  becomes  sugar. 

Next  with  regard  to  the  kind  of  sugar  formed,  it  is,  at  first  at  any 
rate,  not  glucose  but  maltose,  the  formula  for  which  is  C12H22On.  Mal- 
tose is  allied  to  saccharose  or  cane-sugar  more  nearly  than  to  glucose  ;  it 
is  crystalline  ;  its  solution  has  the  property  of  polarizing  light  to  a 
greater  degree  than  solutions  of  glucose  ;  is  not  so  sweet,  and  reduces 
copper  sulphate  less  easily.  It  can  be  converted  into  glucose  by  boiling 
with  dilute  acids,  and  by  the  further  action  of  the  ferment. 

According  to  Brown  and  Heron  the  reactions  may  be   represented 
thus  : — 
One  molecule  of  gelatinous  starch  is  converted  by  the  action  of  an  amy- 

lolytic  ferment  into  n  molecules  of  soluble  starch. 
One  molecule  of  soluble  starch   =10  (C12H20O10)  +  8  (H20),  which  is 
further  converted  by  the  ferment  into 

1.  Erythro-dextrin  (giving  red  with  iodine)  +  Maltose. 
9  (C12H20O10)  (CllH„0Il) 

then  into  2.  Ervthro-dextrin  (giving  yellow  with  iodine)  +  Maltose. 
8(C12H20O10)  2(C15H22On) 

next  into  3.  Achroo-dextrin          +         Maltose. 

7  (Cl2H20O10)  3  (C]2H22On) 

And  so  on  ;  the  resultant  being  : — 

10  (C12H20O,0)   +   8  (H,0)  =  8  (CllHM011)   +  2  (C12H20O10) 
Soluble  starch  Water  Maltose  Achroo-dextrin. 

Test  for  Sugar. — In  such  an  experiment  the  presence  of  sugar  is  at 
once  discovered  by  the  application  of  Trommer's  test,  which  consists  in 
the  addition  of  a  drop  or  two  of  a  solution  of  copper  sulphate,  followed 
by  a  larger  quantity  of  caustic  potash.  When  the  liquid  is  boiled,  an 
orange-red  precipitate  of  copper  suboxide  indicates  the  presence  of  sugar. 

The  action  of  saliva  on  starch  is  facilitated  hy :  (a)  Moderate  heat, 
about  100°  F.  (37.8°  0.).  (b)  A  slightly  alkaline  medium,  (c)  Eemoval 
of  the  changed  material  from  time  to  time.  Its  action  is  retarded  by  (a) 
Cold  ;  a  temperature  of  32°  F.  (0°  C.)  stops  it  for  a  time,  bat  does  not 
destroy  it,  whereas  a  high  temperature  above  140°  F.  (60°  C.)  destroys  it. 

(b)  Acids  or  strong  alkalies  either  delay  or  stop  the  action  altogether. 

(c)  Presence  of  too  much  of  the  changed  material.     Ptyalin,  in  that  it 
converts  starch  into  sugar,  is  an  amylolytic  ferment. 

Starch  appears  to  be  the  only  principle  of  food  upon  which  saliva 
acts  chemically  :  the  secretion  has  no  apparent  influence  on  any  of  the 
other  ternary  principles,  such  as  sugar,  gum,  cellulose,  or  on  fat,  and 
seems  to  be  equally  destitute  of  power  over  albuminous  and  gelatinous 
substances. 

Saliva  from  the  parotid  is  less  viscid,  less  alkine,  clearer,  and  more 
watery  than  that  from  the  submaxillary.  It  has  moreover  a  less  power- 
ful action  on  starch.     Sublingual  saliva  is  the  most  viscid,  and  contains 


DIGESTION.  23? 

more  solids  than  either  of  the  other  two,  but  does  not  appear  to  be  so 
powerful  in  its  action. 

The  salivary  glands  of  children  do  not  become  functionally  active  till 
the  age  of  4  to  6  months,  and  hence  the  bad  effect  of  feeding  them  be- 
fore this  age  on  starchy  food,  corn  flour,  etc.,  which  they  are  unable  to 
render  soluble  and  capable  of  absorption. 

Influence  of  the  Nervous  System. 

The  secretion  of  saliva  is  under  the  control  of  the  nervous  system. 
It  is  a  reflex  action.  Under  ordinary  conditions  it  is  excited  by  the 
stimulation  of  the  peripheral  branches  of  two  nerves,  viz.,  the  gustatory 
or  Ungual  branch  of  the  inferior  maxillary  division  of  the  fifth  nerve, 
and  the  glosso-pharyngeal  part  of  the  eighth  pair  of  nerves,  which  are 
distributed  to  the  mucous  membrane  of  the  tongue  and  pharynx  con- 
jointly. The  stimulation  occurs  on  the  introduction  of  sapid  substances 
into  the  mouth,  and  the  secretion  is  brought  about  in  the  following  way. 
From  the  terminations  of  the  above-mentioned  sensory  nerves  distributed 
in  the  mucous  membrane  an  impression  is  conveyed  upwards  (afferent) 
to  the  special  nerve-centre  situated  in  the  medulla,  which  controls  the 
process,  and  by  it  is  reflected  to  certain  nerves  supplied  to  the  salivary 
glands,  which  will  be  presently  indicated.  In  other  words,  the  centre, 
stimulated  to  action  by  the  sensory  impressions  carried  to  it,  sends  out 
impulses  along  efferent  or  secretory  nerves  supplied  to  the  salivary  glands, 
which  cause  the  saliva  to  be  secreted  by  and  discharged  from  the  gland 
cells.  Other  stimuli,  however,  besides  that  of  the  food,  and  other  sen- 
sory nerves  besides  those  mentioned,  may  produce  reflexly  the  same  ef- 
fects. For  example,  saliva  may  be  caused  to  flow  by  irritation  of  the 
mucous  membrane  of  the  mouth  with  mechanical,  chemical,  electrical, 
or  thermal  stimuli,  also  by  the  irritation  of  the  mucous  membrane  of 
the  stomach  in  some  way,  as  in  nausea,  which  precedes  vomiting,  when 
some  of  the  peripheral  fibres  of  the  vagi  are  irritated.  Stimulation  of 
the  olfactory  nerves  by  smell  of  food,  of  the  optic  nerves  by  the  sight  of 
it,  and  of  the  auditory  nerves  by  the  sounds  which  are  known  by  expe- 
rience to  accompany  the  preparation  of  a  meal,  may  also,  in  the  hungry, 
stimulate  the  nerve-centre  to  action.  In  addition  to  these,  as  a  secretion 
of  saliva  follows  the  movement  of  the  muscles  of  mastication,  it  may  be 
assumed  that  this  movement  stimulates  the  secreting  nerve-fibres  of  the 
gland,  directly  or  reflexly.  From  the  fact  that  the  flow  of  saliva  may  be 
increased  or  diminished  by  mental  emotions,  it  is  evident  that  impres- 
sions from  the  cerebrum  also  are  capable  of  stimulating  the  centre  to  ac- 
tion or  of  inhibiting  its  action. 

Salivary  secretion  may  also  be  excited  by  direct  stimulation  of  the 
centre  in  the  medulla. 


238  HANDBOOK   OF   PHYSIOLOGY. 

A.  On  the  Submaxillary  Gland. — The  submaxillary  gland  has  been 
the  gland  chiefly  employed  for  the  purpose  of  experimentally  demon- 
strating the  influence  of  the  nervous  system  upon  the  secretion  of  saliva, 
because  of  the  comparative  facility  with  which,  with  its  blood-vessels  and 
nerves,  it  may  be  exposed  to  view  in  the  dog,  rabbit,  and  other  animals. 
The  chief  nerves  supplied  to  the  gland  are:  (1)  the  chorda  tympani,  a 
"branch  given  off  from  the  facial  (or  portio  dura  of  the  seventh  pair  of 
nerves),  in  the  canal  through  which  it  passes  in  the  temporal  bone,  in  its 
passage  from  the  interior  of  the  skull  to  the  face;  and  (2)  branches  of 
the  sympathetic  nerve  from  the  plexus  around  the  facial  artery  and  its 
branches  to  the  gland.  The  chorda  (Fig.  178,  ch.  t.),  after  quitting  the 
temporal  bone,  passes  downwards  and  forwards,  under  cover  of  the  ex- 
ternal pterygoid  muscle,  and  joins  at  an  acute  angle  the  lingual  or  gus- 
tatory nerve,  proceeds  with  it  for  a  short  distance,  and  then  passes  along 
the  submaxillary  gland  duct  (Fig.  178,  sm.  d.),  to  which  it  is  distributed, 
giving  branches  to  the  submaxillary  ganglion  (Fig.  178,  sm.  gl.);  and 
sending  others  to  terminate  in  the  superficial  muscles  of  the  tongue.  If 
this  nerve  be  exposed  and  divided  anywhere  in  its  course  from  its  exit 
from  the  skull  to  the  gland,  the  secretion,  if  the  gland  be  in  action,  is 
arrested,  and  no  stimulation  either  of  the  lingual  or  of  the  glosso-pharyn- 
geal  will  produce  a  flow  of  saliva.  But  if  the  peripheral  end  of  the  di- 
vided nerve  be  stimulated,  an  abundant  secretion  of  saliva  ensues,  and 
the  blood-supply  is  enormously  increased,  the  arteries  being  dilated.  The 
veins  even  pulsate,  and  the  blood  contained  within  them  is  more  arterial 
than  venous  in  character. 

When,  on  the  other  hand,  the  stimulus  is  applied  to  the  sympathetic 
filaments  (mere  division  producing  no  apparent  effect),  the  arteries  con- 
tract, and  the  blood  stream  is  in  consequence  much  diminished  ;  and 
from  the  veins,  when  opened,  there  escapes  only  a  sluggish  stream  of 
dark  blood.  The  saliva,  instead  of  being  abundant  and  watery,  becomes 
scanty  and  tenacious.  If.  both  chorda  tympani  and  sympathetic  branches 
be  divided,  the  gland,  released  from  nervous  control,  secretes  continuously 
and  abundantly  (paralytic  secretion). 

The  abundant  secretion  of  saliva,  which  follows  stimulation  of  the 
chorda  tympani,  is  not  merely  the  result  of  a  filtration  of  fluid  from  the 
blood-vessels,  in  consequence  of  the  largely  increased  circulation  through 
them.  This  is  proved  by  the  fact  that,  when  the  main  duct  is  obstructed 
the  pressure  within  may  considerably  exceed  the  blood-pressure  in  the 
arteries,  and  also  that  when  into  the  veins  of  the  animal  experimented 
upon  some  atropin  has  been  previously  injected,  stimulation  of  the  peri- 
pheral end  of  the  divided  chorda  produces  all  the  vascular  effects  as  be- 
fore, without  any  secretion  of  saliva  accompanying  them.  Again,  if  an 
animal's  head  be  cut  off,  and  the  chorda  be  rapidly  exposed  and  stimu- 
lated with  an  interrupted  current,  a  secretion  of  saliva  ensues  for  a  short 


DIGESTION.  239 

time,  although  the  blood-supply  is  necessarily  absent.  These  experi- 
ments serve  to  prove  that  the  chorda  contains  two  sets  of  nerve-fibres, 
one  set  {vaso-dilator)  which,  when  stimulated,  act  upon  a  local  vaso- 
motor centre  for  regulating  the  blood-supply,  inhibiting  its  action,  and 
causing  the  vessels  to  dilate,  and  so  producing  an  increased  supply  of 
blood  to  the  gland;  while  another  set,  which  are  paralyzed  by  injection 
of  atropiu,  directly  stimulate  the  cells  themselves  to  activity,  whereby 
they  secrete  and  discharge  the  constituents  of  the  saliva  which  they 
produce.  These  latter  fibres  very  possibly  terminate  in  the  salivary 
cells  themselves.  If,  on  the  other  hand,  the  sympathetic  fibres  be  di- 
vided, stimulation  of  the  tongue  by  sapid  substances,  or  of  the  trunk  of 
the  lingual,  or  of  the  glossopharyngeal  continues  to  produce  a  flow  of 
saliva.     From  these  experiments  it  is  evident  that  the  chorda  tympani 


Fig.  178.— Diagrammatic  representation  of  submaxillary  gland  of  the  dog  with  its  nerves  and 
blood-vessels.  (This  is  not  intended  to  illustrate  the  exact  anatomical  relations  of  the  several 
structures.)  am.  gld  ,  the  submaxillary  gland  into  the  duct  (sm.  d.)  of  which  a  canula  has  been 
tied.  The  sublingual  gland  and  duct  are  uot  shown;  n.  I.,  n.  I'.,  the  lingual  or  gustatory  nerve; 
ch.  t.,  ch.  f'.,  the  chorda  tympani  proceeding  from  the  facial  nerve,  becoming  conjoined  with  the 
Ungual  at  n.  I'.,  and  afterwards  diverging  and  passing  to  the  gland  along  the  duct;  sm.  gl.,  sub- 
maxillary ganglion  with  its  roots ;  ».  Z.,  the  lingual  nerve  proceeding  to  the  tongue;  o.  car,  the 
cartoid  artery,  two  branches  of  which,  a.  sm.  a.  and  r.  sm.  p.  pass  to  the  anterior  and  posterior 
parts  of  the  gland;  v.  sm..  the  anterior  and  posterior  veins  from  the  gland  ending  in  v.  jr  the  jugu- 
lar vein;  v.  sym  ,  the  conjoined  vagus  and  sympathetic  trunks;  gl.  cer.  s,  the  superior-cervical 
ganglion,  two  branches  of  which  forming  a  plexus,  a.  /.,  over  the  facial  artery,  are  distributed 
(n.  sym.  sm.)  along  the  two  glandular  arteries  to  the  anterior  and  posterior  portion  of  the  gland. 
The  arrows  indicate  the  direction  taken  by  the  nervous  impulses;  during  reflex  stimulations  of  the 
gland  they  ascend  to  the  brain  by  the  lingual  and  descend  by  the  chorda  tympani.   (M.  Foster.  > 

nerve  is  the  principal  nerve  through  which  efferent  impulses  proceed  from 
the  centre  to  excite  the  secretion  of  this  gland. 

The  sympathetic  fibres  appear  to  act  principally  as  a  vaso-constrictor 
nerve;  and  to  exalt  the  action  of  the  local  vaso-motor  centres.  The 
sympathetic  is  moi-e  powerful  in  this  direction  than  the  chorda.  There 
is  not  sufficient  evidence  in  favor  of  the  belief  that  the  submaxillary 


240 


HANDBOOK    OF    PHYSIOLOGY. 


ganglion  is  ever  the  nerve-centre  which  controls  the  secretion  of  the  sub- 
maxillary gland.  '    . 

B.  On  the  Parotid  Gland. — The  nerves  which  influence  secretion  jn 
the  parotid  gland  are  branches  of  the  facial  (lesser  superficial  petrosal) 
and  of  the  S37mpathetic.  The  former  nerve,  after  passing  through  the 
otic  ganglion,  joins  the  auriculo-temporal  branch  of  the  fifth  cerebral 
nerve,  and,  with  it,  is  distributed  to  the  gland.  The  nerves  by  which  the 
stimulus  ordinarily  exciting  secretion  is  conveyed  to  the  medulla  oblon- 
gata, are,  as  in  the  case  of  the  submaxillary  gland,  the  fifth,  and  the 
glossopharyngeal.  The  pneumogastric  nerves  convey  a  further  stimulus 
to  the  secretion  of  saliva,  when  food  has  entered  the  stomach;  the  nerve 
centre  is  the  same  as  in  the  case  of  the  submaxillary  gland. 

Changes  in  the  Gland  Cells. — The  method  by  which  the  salivary  cells, 
produce  the  secretion  of  saliva  appears  to  be  divided  into  two  stages, 
which  differ  somewhat  according  to  the  class  to  which  the  gland  belongs, 
viz.,  whether  to  (1)  the  true  salivary,  or  (2)  to  the  mucous  type.     In  the 


Fig.  179.— Alveoli  of  true  salivary  gland,  a,  at  rest;  b,  in  the  first  stage  cf  secretion;  c,  after 
prolonged  secretion.    (Langley.) 

former  case,  it  has  been  noticed,  as  has  been  already  described  (p.  232), 
that  during  the  rest  which  follows  an  active  secretion  the  lumen  of  the 
alveolus  becomes  smaller,  the  gland  cells  larger,  and  very  granular. 
During  secretion  the  alveoli  and  their  cells  become  smaller,  and  the 
granular  appearance  in  the  latter  to  a  considerable  extent  disappears,  and 
at  the  end  of  secretion,  the  granules  are  confined  to  the  inner  part  of  the 
cell  nearest  to  the  lumen,  which  is  now  quite  distinct  (Fig.  179). 

It  is  supposed  from  these  appearances  that  the  first  stage  in  the  act  of 
secretion  consists  in  the  protoplasm  of  the  salivary  cell  taking  up  from 
the  lymph  certain  materials  from  which  it  manufactures  the  elements  of 
its  own  secretion,  and  which  are  stored  up  in  the  form  of  granules  in  the 
cell  during  rest,  the  second  stage  consisting  of  the  actual  discharge  of 
these  granules,  with  or  without  previous  change.  The  granules  are 
taken  to  represent  the  chief  substance  of  the  salivary  secretion,  i.  e.,  the 
ferment  ptyalin.  In  the  case  of  the  submaxillary  gland  of  the  dog,  at 
any  rate,  the  sympathetic  nerve-fibres  appear  to  have  to  do  with  the  first 
stage  of  the  process,  and  when  stimulated  the  protoplasm  is  extremely 
active  in  manufacturing  the  granules,  whereas  the  chorda  tympani  is 


DIGESTION.  241 

concerned  in  the  production  of  the  second  act,  the  actual  discharge  of 
the  materials  of  secretion,  together  with  a  considerable  amount  of  fluid, 
the  latter  being  an  actual  secretion  by  the  protoplasm,  as  it  ceases  to  oc- 
cur when  atropine  has  been  subcutaneously  injected. 

In  the  mucous-secreting  gland,  the  changes  in  the  cells  during  secre- 
tion have  been  already  spoken  of  (p.  233).  They  consist  in  the  gradual 
secretion  by  the  protoplasm  of  the  cell  of  a  substance  called  mucUjen, 
which  is  converted  into  mucin,  and  discharged  on  secretion  into  the  canal 
of  the  alveoli.  The  mucigen  is,  for  the  most  part,  collected  into  the 
inner  part  of  the  cells  during  rest,  pressing  the  nucleus  and  the  small 
portion  of  the  protoplasm  which  remains,  against  the. limiting  membrane 
of  the  alveoli. 

The  process  of  secretion  in  the  salivary  glands  is  identical  with  that 
of  glands  in  general;  the  cells  which  line  the  ultimate  branches  of  the 
ducts  being  the  agents  by  which  the  special  constituents  of  the  saliva  are 
formed.  The  materials  which  they  have  incorporated  with  themselves 
are  almost  at  once  given  up  again,  in  the  form  of  a  fluid  (secretion), 
which  escapes  from  the  ducts  of  the  gland;  and  the  cells,  themselves, 
undergo  disintegration — again  to  be  renewed,  in  the  intervals  of  the  ac- 
tive exercise  of  their  functions.  The  source  whence  the  cells  obtain  the 
materials  of  their  secretion,  is  the  blood,  or,  to  speak  more  accurately, 
the  plasma,  which  is  filtered  off  from  the  circulating  blood  into  the  in- 
terstices of  the  glands  as  of  all  living  textures. 

The  Pharynx. 

That  portion  of  the  alimentary  canal  which  intervenes  between  the 
mouth  and  the  oesophagus  is  termed  the  Pharynx  (Fig.  164).  It  will 
suffice  here  to  mention  that  it  is  constructed  of  a 
series  of  three  muscles  with  striated  fibres  {con- 
strictors), which  are  covered  by  a  thin  fascia  ex- 
ternally, and  are  lined  internally  by  a  strong  fas- 
cia (pharyngeal  aponeurosis),  on  the  inner  aspect 
of  which  is  areolar  (submucous)  tissue  and  mu- 
cous membrane,  continuous  with  that  of  the 
mouth,  and,  as  regards  the  part  concerned  in  swal- 
lowing, is  identical  with  it  in  general  structure. 
The  epithelium  of  this  part  of  the  pharynx,  like      Hdeorcrypt.  o,  involu- 

r  x  *         *        *  tion    of    mucous    metn- 

that  of  the  mouth,  is  stratified  and  squamous.  brane  with  its  papilla- 

1 .  b,  lymphoid  tissues,  with 

The  pharynx   is   well   supplied   with    mucous      several  lymphoid  sacs, 
glands  (Fig.  182). 

The  Tonsils. 

Between  the  anterior  and  posterior  arches  of  the  soft  palate  are  situ- 
ated the  Tonsils,  one  on  each  side.     A  tonsil  consists  of  an  elevation  of 
1G 


242 


HANDBOOK    OF    PHYSIOLOGY. 


the  mucous  membrane  presenting  12  to  15  orifices,  which  lead  into  crypts 
or  recesses,  in  the  walls  of  which  are  placed  nodules  of  adenoid  or  lym- 
phoid tissue  (Fig.  181).  These  nodules  are  enveloped  in  a  less  dense 
adenoid  tissue  which  reaches  the  mucous  surface.  The  surface  is  covered 
with  stratified  squamous  epithelium,  and  the  subepithelial  or  mucous 
membrane  proper  may  present  rudimentary  papillae  formed  of  adenoid 
tissue.  The  tonsil  is  bounded  by  a  fibrous  capsule  (Fig.  181,  e).  Into 
the  crypts  open  the  ducts  of  numerous  mucous  glands. 


Fig.  181. — Vertical  section  through  a  crypt  of  the  human  tonsil,  a.,  entrance  to  the  crypt" 
which  is  divided  below  by  the  elevation  which  does  not  quite  reach  the  surface;  ft,  stratified  epithe 
Hum;  c,  masses  of  adenoid  tissue ;  d,  mucous  glands  cut  across;  e,  fibrous  capsule.  Semidiagram 
matic.     (V.  D.  Harris.) 

The  viscid  secretion  which  exudes  from  the  tonsils  serves  to  lubricate 
the  bolus  of  food  as  it  passes  them  in  the  second  part  of  the  act  of  deglu- 
tition. 


The  (Esophagus  oe  Gullet. 

The  CEsophagus  or  Gullet  (Fig.  164),  the  narrowest  portion  of  the 
alimentary  canal,  is  a  muscular  and  mucous  tube,  nine  or  ten  inches  in 
length,  which  extends  from  the  lower  end  of  the  pharynx  to  the  cardiac 
orifice  of  the  stomach. 

Structure. — The  oesophagus  is  made  up  of  three  coats — viz.,  the  outer, 
muscular;  the  middle,  submucous;  and  the  inner,  mucous.  The  mus- 
cular coat  (Fig.  183,  g  and  i),  is  covered  externally  by  a  varying  amount 
of  loose  fibrous  tissue.  It  is  composed  of  two  layers  of  fibres,  the  outer 
being  arranged  longitudinally,  and  the  inner  circularly.  At  the  upper 
part  of  the  oesophagus  this  coat  is  made  up  principally  of  striated  muscle 
fibres,  as  they  are  continuous  with  the  constrictor  musclesof  the  pharynx; 
but  lower  down  the  unstriated  fibres  become  more  and  more  numerous, 


DIGESTION. 


243 


and  towards  the  end  of  the  tube  form  the  entire  coat.  The  muscular 
coat  is  connected  with  the  mucous  coat  by  a  more  or  less  developed  layer 
of  areolar  tissue,  which  forms  the  submucous  coat  (Fig.  183,  j),  in  which 
are  contained  in  the  lower  half  or  third  of  the  tube  many  mucous  glands, 
the  ducts  of  which,  passing  through  the  mucous  membrane  (Fig.  183,  c) 
open  on  its  surface.  Separating  this  coat  from  the  mucous  membrane 
proper  is  a  well-developed  layer  of  longitudinal,  unstriated  muscle  (d), 
called  the  muscularis  mucosa.  The  mucous  membrane  is  composed  of  a 
closely  felted  meshwork  of  fine  connective  tissue,  which,  towards  the  sur- 


Fig.  185. 


Fig.  183. 


Fig.  180.— Section  of  a  mucous  gland  from  the  tongue,  a.  opening  of  the  duct  on  the  free  sur- 
face; c,  basement  membrane  with  nuclei;  b,  flattened  epithelial  cells  lining  duct.  The  duct  divides 
into  several  branches,  which  are  convoluted  and  end  blindly,  being  lined  throughout  by  columnar 
epithelium,    d,  lumeu  of  one  of  the  tubuli  of  the  gland.         90.     I  Klein  and  Noble  Smith. 

Fig.  183  -  Longitudinal  section  of  the  oesophagus  of  a  clog  towards  the  lower  end.  a,  stratified 
epithelium  of  the  mucous  membrane;  b,  mucous  membrane  proper;  c,  duct  of  mucous  gland;  d, 
muscularis  muscosse;  e,  mucous  glands;  /,  submucous  coat;  r/,  circular  muscular  layer:  h,  inter- 
muscular layer,  in  which  are  contained  the  ganglion  cells  of  Auerbach;  i,  longitudinal  muscular 
layer;  k,  outside  investment  of  fibrous  tissue.    Semidiagrammatic.    (V.  D.  Harris.  > 


face,  is  elevated  into  rudimentary  papilla.  It  is  covered  with  a  stratified 
epithelium,  of  which  the  most  superficial  layers  are  squamous.  The 
epithelium  is  arranged  upon  a  basement  membrane. 

In  newly-born  children  the  mucous  membrane  exhibits,  in  many  parts, 
the  structure  of  lymphoid  tissue  (Kloiu). 

Blood-  and  lymph-vessels,  and  nerves,  are  distributed  in  the  walls  of 


244  HANDBOOK  OF  PHYOLOGY. 

the  oesophagus.     Between  the  outer  and  inner  layers  of  the  muscular  coat, 
nerve-ganglia  of  Auerbach  are  also  found. 

Deglutition  or   Swallowing. 

When  properly  masticated,  the  food  is  transmitted  in  successive  por- 
tions to  the  stomach  by  the  act  of  deglutition  or  swallowing'.  This, 
for  the  purpose  of  description,  may  be  divided  into  three  acts.  In  the 
first,  particles  of  food  collected  to  a  morsel  are  made  to  glide  between 
the  surface  of  the  tongue  and  the  palatine  arch,  till  they  have  passed  the 
anterior  arch  of  the  fauces;  in  the  second,  the  morsel  is  carried  through 
the  pharynx;  and  in  the  third,  it  reaches  the  stomach  through  the  oesoph- 
agus. These  three  acts  follow  each  other  rapidly.  (1.)  The  first  act 
may  be  voluntary,  although  it  is  usually  performed  unconsciously;  the 
morsel  of  food,  when  sufficiently  masticated,  being  pressed  between  the 
tongue  and  palate,  by  the  agency  of  the  muscles  of  the  former,  in  such  a 
manner  as  to  force  it  back  to  the  entrance  of  the  pharynx.  (2.)  The 
second  act  is  the  most  complicated,  because  the  food  must  pass  by  the 
posterior  orifice  of  the  nose  and  the  upper  opening  of  the  larynx  without 
touching  them.  When  it  has  been  brought,  by  the  first  act,  between  the 
anterior  arches  of  the  palate,  it  is  moved  onwards  by  the  movement  of 
the  tongue  backwards,  and  by  the  muscles  of  the  anterior  arches  contract- 
ing on  it  and  then  behind  it.  The  root  of  the  tongue  being  retracted, 
and  the  larynx  being  raised  with  the  pharynx  and  carried  forwards  under 
the  base  of  the  tongue,  the  epiglottis  is  pressed  over  the  upper  opening 
of  the  larynx,  and  the  morsel  glides  past  it;  the  closure  of  the  glottis 
being  additionally  secured  by  the  simultaneous  contraction  of  its  own 
muscles,  so  that,  even  when  the  epiglottis  is  destroyed,  there  is  little 
danger  of  food  or  drink  passing  into  the  larynx  so  long  as  its  muscles 
can  act  freely.  At  the  same  time,  the  raising  of  the  soft  palate,  so  that 
its  posterior  edge  touches  the  back  part  of  the  pharynx,  and  the  approx- 
imation of  the  sides  of  the  posterior  palatine  arch,  which  move  quickly 
inwards  like  side  curtains,  close  the  passage  into  the  upper  part  of  the 
pharynx  and  the  posterior  nares,  and  form  an  inclined  plane,  along  the 
under  surface  of  which  the  morsel  descends;  then  the  pharynx,  raised  up 
to  receive  it,  in  its  turn  contracts,  and  forces  it  onwards  into  the  oesoph- 
agus. (3.)  In  the  third  act,  in  which  the  food  passes  through  the 
oesophagus,  every  part  of  that  tube,  as  it  receives  the  morsel,  and  is  di- 
lated by  it,  is  stimulated  to  contract;  hence  an  undulatory  contraction 
of  the  oesophagus,  which  is  easily  observable  in  horses  while  drinking, 
proceeds  rapidly  along  the  tube.  It  is  only  when  the  morsels  swallowed 
are  large,  or  taken  too  quickly  in  succession,  that  the  progressive  con- 
traction of  the  oesophagus  is  slow,  and  attended  with  pain.  Division  of 
both  pneumogastric  nerves  paralyzes  the  contractile  power  of  theoesoph- 


DIGESTION. 


245 


agus,  and  food  accordingly  accumulates  in  the  tube.  The  second  and 
third  parts  of  the  act  of  deglutition  are  involuntary. 

Nerve  Mechanism. — The  nerves  engaged  in  the  reflex  act  of  degluti- 
tion axe:— sensory,  branches  of  the  fifth  cerebral  supplying  the  soft  pal- 
ate; glossopharyngeal,  supplying  the  tongue  and  pharynx;  the  superior 
laryngeal  branch  of  the  vagus,  supplying  the  epiglottis  and  the  glottis; 
while  the  motor  fibres  concerned  are: — branches  of  the  fifth,  supplying 
part  of  the  digastric  and  mylo-hyoid  muscles,  and  the  muscles  of  masti- 
cation; the  facial,  supplying  the  levator  palati;  the  glossopharyngeal, 
supplying  the  muscles  of  the  pharynx;  the  vagus,  supplying  the  muscles 
of  the  larynx  through  the  inferior  laryngeal  branch,  and  the  hypoglossal, 
the  muscles  of  the  tongue.  The  nerve-centre  by  which  the  muscles  are 
harmonized  in  their  action,  is  situated  in  the  medulla  oblongata.  In  the 
movements  of  the  oesophagus,  the  ganglia  contained  in  its  walls,  with 
the  pneumo-gastrics,  are  the  nerve-structures  chiefly  concerned. 

It  is  important  to  note  that  the  swallowing  both  of  food  and  drink  is 
a  muscular  act,  and  can,  therefore,  take  place  in  opposition  to  the  force 
of  gravity.  Thus,  horses  and  many  other  animals  habitually  drink  up- 
hill, and  the  same  feat  can  be  performed  by  jugglers. 

The  Stomach. 

In  man  and  those  Mammalia  which  are  provided  with  a  single  stom- 
ach, it  consists  of  a  dilatation  of  the  alimentary  canal  placed  between 


Fig.  184.— Stomach  of  a  sheep,    o?.  oesophagus;  Ru,  rumen;  Ret,  reticulum;  Ps,  psalterium,  or 
manyplies;  A,  abomasum;  Du,  duodenum;  g,  groove  from  oesophagus  to  psalterium.    (Huxley.) 

and  continuous  with  the  oesophagus,  which  enters  its  larger  or  cardiac 
end  on  the  one  hand,  and  the  small  intestine,  which  commences  at  its 
narrowed  end  or  pylorus,  on  the  other.  It  varies  in  shape  and  size  ac- 
cording to  its  state  of  distention. 

The  Ruminants  (ox,  sheep,  deer,  etc.)  possess  very  complex  stom- 
achs; in  most  of  them  four  distinct  cavities  are  to  be  distinguished  (Fig. 
184)! 

1.  The  Paunch  or  Rumen,  a  very  large  cavity  which  occupies  the 
cardiac  end,  and  into  which   large  quantities  of  food  are  in  the  first  in 
.stance  swallowed  with  little  or  no  mastication.     2.   The   Reticulum,  or 


246  HANDBOOK    OF    PHYSIOLOGY. 

Honeycomb  stomach,  so  called  from  the  fact  that  its  mucous  membrane 
is  disposed  in  a  number  of  folds  inclosing  hexagonal  cells.  3.  The 
Psalterium,  or  Manyplies,  in  which  the  mucous  membrane  is  arranged 
in  very  prominent  longitudinal  folds.  4.  Abomasum ,  Reed,  or  Rennet, 
narrow  and  elongated,  its  mucous  membrane  being  much  more  highly 
vascular  than  that  of  the  other  divisions.  In  the  process  of  rumination 
small  portions  of  the  contents  of  the  rumen  and  reticulum  are  succes- 
sively regurgitated  into  the  mouth,  and  there  thoroughly  masticated  and 
insalivated  (chewing  the  cud):  they  are  then  again  swallowed,  being  this 
time  directed  by  a  groove  (which  in  the  figure  is  seen  running  from  the 
lower  end  of  the  oesophagus)  into  the  manyplies,  and  thence  into  the 
abomasum.  It  will  thus  be  seen  that  the  first  two  stomachs  (paunch  and 
reticulum)  have  chiefly  the  mechanical  functions  of  storing  and  moisten- 
ing the  fodder:  the  third  (manyplies)  probably  acts  as  a  strainer,  only 
allowing  the  finely  divided  portions  of  food  to  pass  on  into  the  fourth 
stomach,  where  the  gastric  juice  is  secreted  and  the  process  of  digestion 
carried  on.  The  mucous  membrane  of  the  first  three  stomachs  is 
lowly  vascular,  while  that  of  the  fourth  is  pulpy,  glandular,  and  highly 
vascular. 

In  some  other  animals,  as  the  pig,  a  similar  distinction  obtains  be- 
tween the  mucous  membrane  in  different  parts  of  the  stomach. 

In  the  pig  the  glands  in  the  cardiac  end  are  few  and  small,  while  to- 
wards the  pylorus  they  are  abundant  and  large. 

A  similar  division  of  the  stomach  into  a  cardiac  (receptive)  and  a 
pyloric  (digestive)  part,  foreshadowing  the  complex  stomach  of  rumi- 
nants, is  seen  in  the  common  rat,  in  which  these  two  divisions  of  the 
stomach  are  distinguished,  not  only  by  the  characters  of  their  lining 
membrane,  but  also  by  a  well-marked  constriction. 

In  birds  the  function  of  mastication  is  performed  by  the  stomach 
(gizzard)  which  in  granivorous  orders,  e.g.,  the  common  fowl,  possesses, 
very  powerful  muscular  walls  and  a  dense  horny  epithelium. 

Structure. — The  stomach  is  composed  of  four  coats,  called  respec- 
tively— an  external  or  (1)  peritoneal,  (2)  muscular,  (3)  submucous,  and 
(4)  mucous  coat ;  with  blood-vessels,  lymphatics,  and  nerves  distributed 
in  and  between  them. 

(1)  The  peritoneal  coat  has  the  structure  of  serous  membranes  in 
general.  (2)  The  muscular  coat  consists  of  three  separate  layers  or  sets  of 
fibres,  which,  according  to  their  several  directions,  are  named  the  longi- 
tudinal, circular,  and  oblique.  The  longitudinal  set  are  the  most  superfi- 
cial :  they  are  continuous  with  the  longitudinal  fibres  of  the  oesophagus, 
and  spread  out  in  a  diverging  manner  over  the  cardiac  end  and  sides  of 
the  stomach.  They  extend  as  far  as  the  pylorus,  being  especially  dis- 
tinct at  the  lesser  or  upper  curvature  of  the  stomach,  along  which  they 
pass  in  several  strong  bands.  The  next  set  are  the  circular  or  transverse 
fibres,  which  more  or  less  completely  encircle  all  parts  of  the  stomach  ; 
they  are  most  abundant  at  the  middle  and  in  the  pyloric  portion  of  the 
organ,  and  form  the  chief  part  of  the  thick  projecting  ring  of  the  py- 
lorus.    These  fibres  are  not  simple  circles,  but  form  double  or  figure- 


DIGESTION. 


24:7 


of-8  loops,  the  fibres  intersecting  very  obliquely.  The  next,  and  conse- 
quently deepest  set  cf  fibres,  are  the  oblique,  continuous  with  the  circular 
muscular  fibres  of  the  oesophagus,  and  having  the  same  double-looped 
arrangement  that  prevails  in  the  preceding  layer  :  they  are  comparatively 
few  in  number,  and  are  placed  only  at 
the  cardiac  orifice  and  portion  of  the 
stomach,  over  both  surfaces  of  which 
they  are  spread,  some  passing  ob- 
liquely from  left  to  right,  others  from 
right  to  left,  around  the  cardiac  ori- 
fice, to  which,  by  their  interlacing, 
they  form  a  kind  of  sphincter,  con- 
tinuous with  that  around  the  lower 
end  of  the  oesophagus.  The  mus- 
cular fibres  of  the  stomach  and  of  the 
intestinal  canal  are  unstriated,  being 
composed  of  elongated,  spindle-shaped 
fibre-cells. 

(3)  and  (4)  The  mucous  membrane 
of  the  stomach,  which  rests  upon  a 
layer  of  loose  cellular  membrane,  or 
submucous  tissue,  is  smooth,  level, 
soft,  and  velvety;  of  a  pale  pink  color 
during  life,  and  in  the  contracted 
state  thrown  into  numerous,  chiefly 
longitudinal,  folds  or  rugae,  which 
disappear  when  the  organ  is  dis- 
tended. 

The  basis  of  the  mucous  mem- 
brane is  a  fine  connective  tissue,  which 
approaches  closely  in  structure  to 
adenoid  tissue  ;  this  tissue  supports 
the  tubular  glands  of  which  the  su- 
perficial and  chief  part  of  the  mucous 
membrane  is  composed,  and  passing 
up  between  them  assists  in  "binding 
them  together.  Here  and  there  are 
to  be  found  in  this  coat,  immedi- 
ately underneath  the  glands,  masses  of 
adenoid  tissue  sufficiently  marked 
to  be  termed  by  some  lymphoid  follicles.  The  glands  are  separated  from 
the  rest  of  the  mucous  membrane  by  a  very  fine  homogeneous  basement 
membrane. 

At  the  deepest  part  of  the  mucous  membrane  are  two  layers  (circular 


Fig.  185.—  From  a  vertical  section  through 
the  mucous  membrane  of  the  cardiac  end  of 
stomach.  Two  peptic  glands  are  shown 
with  a  duct  common  to  both,  one  gland  only 
in  part.  «,  duct  with  columnar  epithelium 
becoming  shorter  as  the  cells  are  traced 
downward;  n,  neck  of  gland  tubes,  with 
central  and  parietal  or  so-called  peptic  cells; 
b,  fundus  with  curved  csecal  extremity— 
the  parietal  cells  are  not  so  numerous  here. 
X  400.    cKlein  and  Noble  Smith.  > 


248  HANDBOOK    OF    rH\SIOLOGY= 

and  longitudinal)  of  unstriped  muscular  fibres,  called  the  muscularis 
mucosa,  which  separate  the  mucous  membrane  from  the  scanty  submu- 
cous tissue. 

When  examined  with  a  lens,  the  internal  or  free  surface  of  the  stomach 
presents  a  peculiar  honeycomb  appearance,  produced  by  shallow  polyg- 
onal depressions,  the  diameter  of  which  varies  generally  from  -^^th  to 
■g-ly-th  of  an  inch;  but  nearer  the  pylorus  is  as  much  as  y^th  of  an  inch. 
They  are  separated  by  slightly  elevated  ridges,  which  sometimes,  espe- 
cially in  certain  morbid  states  of  the  stomach,  bear  minute,  narrow  vas- 
cular processes,  which  look  like  villi,  and  have  given  rise  to  the  errone- 
ous supposition  that  the  stomach  has  absorbing  villi,  like  those  of  the 
small  intestines.  In  the  bottom  of  these  little  pits,  and  to  some  extent 
between  them,  minute  openings  are  visible,  which  are  the  orifices  of  the 
ducts  of  perpendicularly  arranged  tubular  glands  (Fig.  185),  imbedded 
side  by  side  in  sets  or  bundles,  on  the  surface  of  the  mucous  membrane, 
and  composing  nearly  the  whole  structure. 

Gastric  Glands. — Of  these  there  are  two  varieties,  (a)  Peptic,  (i) 
Pyloric  or  Mucous. 

(a)  Peptic  glands  are  found  throughout  the  whole  of  the  stomach 

except  at  the  pylorus.  They  are  arranged 
in  groups  of  four  or  five,  which  are  sepa- 
rated by  a  fine  connective  tissue.  Two  or 
three  tubes  often  open  into  one  duct, 
which  forms  about  a  third  of  the  whole 
length  of  the  tube  and  opens  on  the  sur- 
face. The  ducts  are  lined  with  columnar 
c — "J"i£r^llr  ^~^^^^^^.        epithelium.     Of  the   gland  tube  proper, 

Fig,     186. -Transverse     section      ?•  6.,  the  part  of  the  gland  below  the  duct, 

through  lower  part  of  peptic  glands     the  upper  third  is  the  neck  and  the  rest 

of    a  cat.    a,   peptic  cells;    b,   small  ^* 

spheroidal  or  cubical  ceils;  c,  transverse     the  body.     The  neck  is  narrower  than  the 

section  of  capillaries.    (Frey. )  .        .  . 

body,  and  is  lined  with  granular  cubical 
cells  which  are  continuous  with  the  columnar  cells  of  the  duct.  Between 
these  cells  and  the  membrana  propria  of  the  tubes,  are  large  oval  or 
spherical  cells,  opaque  or  granular  in  appearance,  with  clear  oval  nuclei, 
bulging  out  the  membrana  propria;  these  cells  are  called  peptic  or  parie- 
tal cells.  They  do  not  form  a  continuous  layer.  The  body,  which  is 
broader  than  the  neck  and  terminates  in  a  blind  extremity  or  fundus 
near  the  muscularis  mucosae,  is  lined  by  cells  continuous  with  the  cu- 
bical or  central  cells  of  the  neck,  but  longer,  more  columnar  and  more 
transparent.  In  this  part  are  a  few  parietal  cells  of  the  same  kind  as  in 
the  neck  (Fig.  185). 

As  the  pylorus  is  approached  the  gland  ducts  become  longer,  and 
the  tube  proper  becomes  shorter,  and  occasionally  branched  at  the  fun- 
dus. 


DIGESTION. 


249 


(b)  Pyloric  Glands. — These  glands  (Fig.  187).  have  much  longer 
ducts  than  the  peptic  glands.  Into  each  duct  two  or  three  tubes  open 
by  very  short  and  narrow  necks,  and  the  body  of  each  tube  is  branched, 
wavy,  and  convoluted.  The  lumen  is  very  large.  The  ducts  are  lined 
with  columnar  epithelium,  and  the  neck  and  body  with  shorter  and 
more  granular  cubical  cells,  which  correspond  with  the  central  cells  of 
the  peptic  glands.  During  secretion  the  cells  become,  as  in  the  case  of 
the  peptic  glands,  larger,  and  the  granules  restricted  to  the  inner  zone 
of  the  cell.  As  they  approach  the  duodenum  the  pyloric  glands  become 
larger,  more  convoluted,  and  more  deeply  situated.  They  are  directly 
continuous  with  Brunner's  glands  in  the  duodenum.     (Watney.) 


UM 


Fig  1ST 


Fig.  188. 


Fig.  187.— Section  showing  the  pyloric  glands,  s,  free  surface;  d,  ducts  of  pyloric  glands;  n, 
neck  of  same;  m,  the  gland  alveoli;  mm,  muscularis  mucosae.    (Klein  and  Noble  Smith.) 

Fig.  188.  -Plan  of  the  bloodvessels  of  the  stomach,  as  they  would  be  seen  in  a  vertical  section. 
a,  arteries,  passing  up  from  the  vessels  of  submucous  coat:  b.  capillaries  branching  between  and 
around  the  tubes;  c.  superficial  plexus  of  capillaries  occupying  the  ridges  of  the  mucous  membrane; 
d,  veins  formed  by  the  union  of  veins  whieh.  having  collected  the  blood  of  the  superficial  capillary 
plexus,  are  seen  passing  down  between  the  tubes.    (Brinton.j 


Changes  in  the  gland  cells  during  secretion. — The  chief  or  cubical 
cells  of  the  peptic  glands,  and  the  corresponding  cells  of  the  pyloric 
glands  during  the  early  stage  of  digestion,  if  hardened  in  alcohol,  appear 
swollen  and  granular,  and  stain  readily.  At  a  later  stage  the  cells  be- 
come smaller,  but  more  granular  and  stain  even  more  readily.  The 
parietal  cells  swell  up,  but  are  otherwise  not  altered  during  digestion. 
The  granules,  however,  in  the  alcohol-hardened  specimen,  are  believed 
not  to  exist  in  the  living  cells,  but  to  have  been  precipitated  by  the  hard- 


250  HANDBOOK   OF    PHYSIOLOGY. 

ening  reagent;  for  if  examined  during  life  they  appear  to  be  confined 
to  the  inner  zone  of  the  cells,  and  the  outer  zone  is  free  from  granules, 
whereas  during  rest  the  cell  is  granular  throughout.  These  granules  are 
thought  to  be  pepsin,  or  the  substance  from  which  pepsin  is  formed, 
pepsinogen,  which  is  during  rest  stored  chiefly  in  the  inner  zone  of  the 
cells  and  discharged  into  the  lumen  of  the  tube  during  secretion.  (Lang- 
ley.) 

Lymphatics. — Lymphatic  vessels  surround  the  gland  tubes  to  a 
greater  or  less  extent.  Towards  the  fundus  of  the  peptic  glands  are 
found  masses  of  lymphoid  tissue,  which  may  appear  as  distinct  follicles, 
somewhat  like  the  solitary  glands  of  the  small  intestine. 

Blood-vessels. — The  blood-vessels  of  the  stomach,  which  first  break 
up  in  the  submucous  tissue,  send  branches  upward  between  the  closely 
packed  glandular  tubes,  anastomosing  around  them  by  means  of  a  fine 
capillary  network,  with  oblong  meshes.  Continuous  with  this  deeper 
plexus,  or  prolonged  upwards  from  it,  so  to  speak,  is  a  more  superficial 
network  of  larger  capillaries,  which  branch  densely  around  the  orifices 
of  the  tubes,  and  form  the  framework  on  which  are  moulded  the  small 
elevated  ridges  of  mucous  membrane  bounding  the  minute,  polygonal 
pits  before  referred  to.  From  this  superficial  network  the  veins  chiefly 
take  their  origin.  Thence  passing  down  between  the  tubes  with  no  very 
free  connection  with  the  deeper  intertubular  capillary  plexus,  they  open 
finally  into  the  venous  network  in  the  submucous  tissue. 

Nerves. — The  nerves  of  the  stomach  are  derived  from  the  pneumo- 
gastric  and  sympathetic,  and  form  a  plexus  in  the  submucous  and  mus- 
cular coats,  containing  many  ganglia  (Eemak,  Meissner). 

Gastric  Juice.  . 

Gastric  Juice. — The  functions  of  the  stomach  are  to  secrete  a  digest- 
ive fluid  (gastric  juice),  to  the  action  of  which  the  food  is  subjected  after 
it  has  entered  the  cavity  of  the  stomach  from  the  oesophagus;  to  thor- 
oughly incorporate  the  fluid  with  the  food  by  means  of  its  muscular 
movements;  and  to  absorb  such  substances  as  are  ready  for  absorption. 
While  the  stomach  contains  no  food,  and  is  inactive,  no  gastric  fluid  is 
secreted;  and  mucus,  which  is  either  neutral  or  slightly  alkaline,  covers 
its  surface.  But  immediately  on  the  introduction  of  food  or  other  sub- 
stance the  mucous  membrane,  previously  quite  pale,  becomes  slightly 
turgid  and  reddened  with  the  influx  of  a  larger  quantity  of  blood;  the 
gastric  glands  commence  secreting  actively,  and  an  acid  fluid  is  poured 
out  in  minute  drops,  which  gradually  run  together  and  flow  down  the 
walls  of  the  stomach,  or  soak  into  the  substances  within  it. 

Chemical  Composition. — The  first  accurate  analysis  of  gastric  juice 
was  made  by  Prout:  but  it  does  not  appear  to  have  been  collected  in  any 
large  quantity,  or  pure  and  separate  from  food,  until  the  time  when 


DIGESTION.  251 

Beaumont  was  enabled,  by  a  fortunate  circumstance,  to  obtain  it  from 
the  stomach  of  a  man  named  St.  Martin,  in  whom  there  existed,  as  the 
result  of  a  gunshot  wound,  an  opening  leading  directly  into  the  stomach, 
near  the  upper  extremity  of  the  great  curvature,  and  three  inches  from 
the  cardiac  orifice.  The  introduction  of  any  mechanical  irritant,  such 
as  the  bulb  of  a  thermometer,  into  the  stomach,  through  this  artificial 
opening,  excited  at  once  the  secretion  of  gastric  fluid.  This  was  drawn 
off,  and  was  often  obtained  to  the  extent  of  nearly  an  ounce.  The  in- 
troduction of  alimentary  substauces  caused  a  much  more  rapid  and 
abundant  secretion  than  did  other  mechanical  irritants.  No  increase  of 
temperature  "could  be  detected  during  the  most  active  secretion;  the  ther- 
mometer introduced  into  the  stomach  always  stood  at  100°  F.  (37.8° 
C.)  except  during  muscular  exertion,  when  the  temperature  of  the 
stomach,  like  that  of  other  parts  of  the  body,  rose  one  or  two  degrees 
higher. 

The  chemical  composition  of  human  gastric  juice  has  been  also  in- 
vestigated by  Schmidt.  The  fluid  in  this  case  was  obtained  by  means  of 
an  accidental  gastric  fistula,  which  existed  for  several  years  below  the 
left  mammary  region  of  a  patient  between  the  cartilages  of  the  ninth  and 
tenth  ribs.  The  mucous  membrane  was  excited  to  action  by  the  intro- 
duction of  some  hard  matter,  such  as  dry  peas,  and  the  secretion  was  re- 
moved by  means  of  an  elastic  tube.  The  fluid  thus  obtained  was  found 
to  be  acid,  limpid,  odorless,  with  a  mawkish  taste — with  a  specific  gravity 
of  1002,  or  a  little  more.  It  contained  a  few  cells,  seen  with  the  micro- 
scope, and  some  fine  granular  matter.  The  analysis  of  the  fluid  obtained 
in  this  way  is  given  below.  The  gastric  juice  of  dogs  and  other  animals 
obtained  by  the  introduction  into  the  stomach  of  a  clean  sponge  through 
an  artifically  made  gastric  fistula,  shows  a  decided  difference  in  compo- 
sition, but  possibly  this  is  due,  at  least  in  part,  to  admixture  with  food. 

Chemical  Composition  of  Gastric  Juice. 


Dogs. 

Human. 

Water, 

971.17 

9944 

Solids, 

28.82 

5-39 

Solids- 

Ferment— Pepsin,     .... 

17.5 

3.19 

Hydrochloric  acid  (free), 

2,7 

.2 

Salts- 

Calcium,  sodium,  and  potassium,  chlor- 

ides; and  calcium,  magnesium,  and 

iron,  phosphates,       .... 

8.57 

2.18 

The  quantity  of  gastric  juice  secreted  daily  has  been  variously  esti- 
mated ;  but  the  average  for  a  healthy  adult  may  be  assumed  to  range 
from  ten  to  twenty  pints  in  the  twenty-four  hours.     The  acidity  of  the 


:252  handbook  of  physiology. 

fluid  is  due  to  free  hydrochloric  acid,  although  other  acids,  e.g.,  lactic, 
acetic,  butyric,  are  not  unfrequently  to  be  found  therein  as  products  of 
gastric  digestion  or  abnormal  fermentation.  The  amount  of  hydro- 
chloric acid  varies  from  2  to  .2  per  1000  parts.  In  healthy  gastric  juice 
the  amount  of  free  acid  may  be  as  much  as  .2  per  cent. 

As  regards  the  formation  of  pepsin  and  acid,  the  former  is  produced 
by  the  central  or  chief  cells  of  the  peptic  glands,  and  also  most  likely  by 
the  similar  cells  in  the  pyloric  glands  ;  the  acid  is  chiefly  found  at  the 
surface  of  the  mucous  membrane,  but  is  in  all  probability  formed  by  the 
secreting  action  of  the  parietal  cells  of  the  peptic  glands,  as  no  acid  is 
formed  by  the  pyloric  glands  in  which  this  variety  of  cell  is  absent. 

The  ferment  Pepsin  can  be  prepared  by  digesting  portions  of  the  mu- 
cous membrane  of  the  stomach  in  cold  water,  after  they  have  been  mace- 
rated for  some  time  in  water  at  a  temperature  80°-100°  F.  (27.°-37.8° 
C).  The  warm  water  dissolves  various  substances  as  well  as  some  of  the 
pepsin,  but  the  cold  water  takes  up  little  else  than  pepsin,  which  is  con- 
tained in  a  grayish-brown  viscid  fluid,  on  evaporating  the  cold  solution. 
The  addition  of  alcohol  throws  down  the  pepsin  in  grayish-white  ffocculi. 
Glycerin  also  has  the  property  of  dissolving  out  the  ferment ;  and  if 
the  mucous  membrane  be  finely  minced,  and  the  moisture  removed  by 
absolute  alcohol,  a  powerful  extract  may  be  obtained  by  throwing  into 
glycerin. 

Functions  — The  digestive  power  of  the  gastric  juice  depends  on  the 
pepsin  and  acid  contained  in  it,  both  of  which  are,  under  ordinary  cir- 
cumstances, necessary  for  the  process. 

The  general  effect  of  digestion  in  the  stomach  is  the  conversion  of  the 
food  into  chyme,  a  substance  of  various  composition  according  to  the  na- 
ture of  the  food,  yet  always  presenting  a  characteristic  thick,  pultaceous, 
grumous  consistence,  with  the  undigested  portions  of  the  food  mixed  in 
a  more  fluid  substance,  and  a  strong,  disagreeable  acid  odor  and  taste. 

The  chief  function  of  the  gastric  juice  is  to  convert  proteids  into  pep- 
tones. This  action  maybe  shown  by  adding  a  little  gastric  juice  (natural 
or  artificial)  to  some  diluted  egg-albumin,  and  keeping  the  mixture  at  a 
temperature  of  about  100°  F.  (37.8°  C.) ;  it  is  soon  found  that  the  albu- 
min cannot  be  precipitated  on  boiling,  but  that  if  the  solution  be  neu- 
tralized with  an  alkali,  a  precipitate  of  acid-albumin  is  thrown  down. 
After  a  while  the  proportion  of  acid-albumin  gradually  diminishes,  so 
that  at  last  scarcely  any  precipitate  results  on  neutralization,  and  finally 
it  is  found  that  all  the  albumin  has  been  changed  into  another  proteid 
substance  which  is  not  precipitated  on  boiling  or  on  neutralization. 
This  is  called  peptone. 

Characteristics  of  Peptones. — Peptones  have  certain  characteristics 
which  distinguish  them  from  other  proteids.  1.  They  are  diffusible,  i.  e., 
they  possess  the  property  of  passing  through  animal  membranes.     2. 


DIGESTION.  253 

They  cannot  be  precipitated  by  heat,  by  nitric,  or  acetic  acid,  or  by  po- 
tassium ferrocyanide  and  acetic  acid.  They  are,  however,  thrown  down 
by  tannic  acid,  by  mercuric  chloride  and  by  picric  acid.  3.  They  are 
very  soluble  in  water  and  in  neutral  saline  solutions. 

In  their  diffusibility  peptones  differ  remarkably  from  egg-albumin, 
and  on  this  diffusibility  depends  one  of  their  chief  uses.  Egg-albumin 
as  such,  even  in  a  state  of  solution,  would  be  of  little  service  as  food,  in- 
asmuch as  its  indiffusibility  would  effectually  prevent  its  passing  by  ab- 
sorption into  the  blood-vessels  of  the  stomach  and  intestinal  canal. 
Changed,  however,  by  the  action  of  the  gastric  juice  into  peptones,  albu- 
minous matters  diffuse  readily,  and  are  thus  quickly  absorbed. 

After  entering  the  blood  the  peptones  are  very  soon  again  modified, 
so  as  to  re-assume  the  chemical  characters  of  albumin,  a  change  as  neces- 
sary for  preventing  their  diffusing  out  of  the  blood-vessels,  as  the  pre 
vious  change  was  for  enabling  them  to  pass  in.     This  is  effected,  proba- 
bly, in  great  part  by  the  agency  of  the  liver. 

Products  of  Gastric  Digestion. — The  chief  product  of  gastric  diges- 
tion is  undoubtedly  peptone.  We  have  seen,  however,  in  the  above 
experiment  that  there  is  a  by-product,  and  this  is  almost  identical  with 
syntonin  or  acid  albumin.  This  body  is  probably  not  exactly  identical, 
however,  with  syntonin,  and  its  old  name  of  parapeptone  had  better  be 
retained.  The  conversion  of  native  albumin  into  acid-albumin  may  be 
effected  by  the  hydrochloric  acid  alone,  but  the  further  action  is  un- 
doubtedly due  to  the  ferment  and  the  acid  together,  as  although  under 
high  pressure  any  acid  solution  may,  it  is  said,  if  strong  enough,  produce 
the  entire  conversion  into  peptone,  under  the  condition  of  digestion  in  the 
stomach  this  would  be  quite  impossible  ;  and,  on  the  other  hand,  pepsin 
will  not  act  without  the  presence  of  acid.  The  production  of  two  forms 
of  peptone  is  usually  recognized,  called  respectively  «»ii-peptone  and 
Zw>M-peptone.  Their  differences  in  chemical  properties  have  not  yet 
been  made  out,  but  they  are  distinguished  by  this  remarkable  fact,  that 
the  pancreatic  juice,  while  possessing  no  action  over  the  former,  is  able 
to  convert  the  latter  into  leucin  and  tyrosin.  Pepsin  acts  the  part  of  a 
hydrolytic  ferment  (proteolytic),  and  appears  to  cause  hydration  of  al- 
bumin, peptone  being  a  highly  hyd rated  form  of  albumin. 

Circumstances  favoring  Gaslric  Digestion.  1.  A  temperature  of 
about  100°  F.  (37.8°  C.)  ;  at  31°  F.  (0°  C.)  it  is  delayed,  and  by  boiling 
is  altogether  stopped.  2.  An  acid  medium  is  necessary.  Hydrochloric 
is  the  best  acid  for  the  purpose.  Excess  of  acid  or  neutralization  stops 
the  process.  3.  The  removal  of  the  products  of  digestion.  Excess  of 
peptone  delays  the  action. 

Action  of  the  Gastric  Juice  on  Bodies  other  than  Proteids. — All  pro- 
teids  are  converted  by  the  gastric  juice  into  peptones,   and,  therefore. 


"254:  HANDBOOK    OF  PHYSIOLOGY. 

whether  they  be  taken  into  the  body  in  meat,  eggs,  milk,  bread,  or  other 
foods,  the  resultant  still  is  peptone. 

Milk  is  curdled,  the  casein  being  precipitated,  and  then  dissolved. 
The  curdling  is  due  to  a  special  ferment  of  the  gastric  juice  (curdling  or 
rennet  ferment),  and  is  not  due  to  the  action  of  the  free  acid  only.  The 
effect  of  rennet,  which  is  a  decoction  of  the  fourth  stomach  of  a  calf  in 
brine,  has  long  been  known,  as  it  is  used  extensively  to  cause  precipita- 
tion of  casein  in  cheese  manufacture.  The  ferment  which  produces  this 
curdling  action  is  distinct  from  pepsin. 

Gelatin  is  dissolved  and  changed  into  peptone,  as  are  also  chondrin 
and  elastin ;  but  Mucin,  and  the  Horny  tissues,  which  contain  keratin 
generally  are  unaffected. 

On  the  Amylaceous  articles  of  food,  and  upon  pure  Oleaginous  prin- 
ciples, the  gastric  juice  has  no  action.  In  the  case  of  adipose  tissue,  its 
effect  is  to  dissolve  the  areolar  tissue,  albuminous  cell- walls,  etc.,  which 
enter  into  its  composition,  by  which  means  the  fat  is  able  to  mingle  more 
uniformly  with  the  other  constituents  of  the  chyme. 

The  gastric  fluid  acts  as  a  general  solvent  for  some  of  the  saline  con- 
stituents of  the  food,  as,  for  example,  particles  of  common  salt,  which 
may  happen  to  have  escaped  solution  in  the  saliva  ;  while  its  acid  may 
enable  it  to  dissolve  some  other  salts  which  are  insoluble  in  the  latter  or 
in  water.  It  also  dissolves  cane  sugar,  and  by  the  aid  of  its  mucus 
causes  its  conversion  in  part  into  grape  sugar. 

The  action  of  the  gastric  juice  in  preventing  and  checking  putrefac- 
tion has  been  often  directly  demonstrated.  Indeed,  that  the  secretions 
which  the  food  meets  with  in  the  alimentary  canal  are  antiseptic  in 
their  action,  is  what  might  be  anticipated,  not  only  from  the  proneness 
to  decomposition  of  organic  matters,  such  as  those  used  as  food,  espe- 
cially under  the  influence  of  warmth  and  moisture,  but  also  from  the 
well-known  fact  that  decomposing  flesh  (e.  g.,  high  game)  may  be  eaten 
with  impunity,  while  it  would  certainly  cause  disease  were  it  allowed  to 
enter  the  blood  by  any  other  route  than  that  formed  by  the  organs  of 
digestion. 

Time  occupied  in  Gastric  Digestion. — Under  ordinary  conditions, 
from  three  to  four  hours  may  be  taken  as  the  average  time  occupied  by 
the  digestion  of  a  meal  in  the  stomach.  But  many  circumstances  will 
modify  the  rate  of  gastric  digestion.  The  chief  are  :  the  nature  of  the 
food  taken  and  its  quantity  (the  stomach  should  be  fairly  filled — not 
distended)  ;  the  time  that  has  elapsed  since  the  last  meal,  which  should 
be  at  least  enough  for  the  stomach  to  be  quite  clear  of  food;  the  amount 
of  exercise  previous  and  subsequent  to  a  meal  (gentle  exercise  being  fa- 
vorable, over-exertion  injurious  to  digestion)  ;  the  state  of  mind  (tran- 
quillity of  temper  being  essential,  in  most  cases,  to  a  quick  and  due  di- 
gestion) ;  the  bodily  health  ;  and  some  others. 


DIGESTION.  255 

Movements  of  the  Stomach. — The  gastric  fluid  is  assisted  in  accom- 
plishing its  share  in  digestion  by  the  movements  of  the  stomach.  In 
granivorous  birds,  for  example,  the  contraction  of  the  strong  muscular 
gizzard  affords  a  necessary  aid  to  digestion,  by  grinding  and  triturating 
the  hard  seeds  which  constitute  part  of  the  food.  But  in  the  stomachs 
of  man  and  other  Mammalia  the  movements  of  the  muscular  coat  are 
too  feeble  to  exercise  any  such  mechanical  force  on  the  food  ;  neither 
are  they  needed,  for  mastication  has  already  done  the  mechanical  work 
of  a  gizzard  ;  and  experiments  have  demonstrated  that  substances  are 
digested  even  inclosed  in  perforated  tubes,  and  consequently  protected 
from  mechanical  influence. 

The  normal  actions  of  the  muscular  fibres  of  the  human  stomach  ap- 
pear to  have  a  three-fold  purpose  :  (1)  to  adapt  the  stomach  to  the  quan- 
tity of  food  in  it,  so  that  its  walls  may  be  in  contact  with  the  food  on 
all  sides,  and,  at  the  same  time,  may  exercise  a  certain  amount  of  com- 
pression upon  it;  (2)  to  keep  the  orifices  of  the  stomach  closed  until  the 
food  is  digested  ;  and  (3)  to  perform  certain  peristaltic  movements, 
whereby  the  food,  as  it  becomes  chymified,  is  gradually  propelled  to- 
wards, and  ultimately  through,  the  pylorus.  In  accomplishing  this  lat- 
ter end,  the  movements  without  doubt  materially  contribute  towards 
effecting  a  thorough  intermingling  of  the  food  and  the  gastric  fluid. 

When  digestion  is  not  going  on,  the  stomach  is  uniformly  contracted, 
its  orifices  not  more  firmly  than  the  rest  of  its  walls  ;  but,  if  examined 
shortly  after  the  introduction  of  food,  it  is  found  closely  encircling  its 
contents,  and  its  orifices  are  firmly  closed  like  sphincters.  The  cardiac 
orifice,  every  time  food  is  swallowed,  opens  to  admit  its  passage  to  the 
stomach,  and  immediately  again  closes.  The  pyloric  orifice,  during  the 
first  part  of  gastric  digestion,  is  usually  so  completely  closed,  that  even 
when  the  stomach  is  separated  from  the  intestines,  none  of  its  contents 
escape.  But  towards  the  termination  of  the  digestive  process,  the  py- 
lorus seems  to  offer  less  resistance  to  the  passage  of  substances  from  the 
stomach  ;  first  it  yields  to  allow  the  successively  digested  portions  to  go 
through  it ;  and  then  it  allows  the  transit  of  even  undigested  substances. 
It  appears  that  food,  so  soon  as  it  enters  the  stomach,  is  subjected  to 
a  kind  of  peristaltic  action  of  the  muscular  coat,  whereby  the  digested 
portions  are  gradually  moved  towards  the  pylorus.  The  movements 
were  observed  to  increase  in  rapidity  as  the  process  of  chymification  ad- 
vanced, and  were  continued  until  it  was  completed. 

The  contraction  of  the  fibres  situated  towards  the  pyloric  end  of  the 
stomach  seems  to  be  more  energetic  and  more  decidedly  peristaltic  than 
those  of  the  cardiac  portion.  Thus,  it  was  found  in  the  case  of  St.  Mar- 
tin, that  when  the  bulb  of  the  thermometer  was  placed  about  three 
inches  from  the  pylorus,  through  the  gastric  fistula,  it  was  tightly  em- 
braced from  time  to  time,  and  drawn  towards  the  pyloric  orifice  for  a 


256  HANDBOOK    OF    PHYSIOLOGY. 

distance  of  three  or  four  inches.  The  object  of  this  movement  appears1 
to  be,  as  just  said,  to  carry  the  food  towards  the  pylorus  as  fast  as  it  is 
formed  into  chyme,  and  to  propel  the  chyme  into  the  duodenum  ;  the 
undigested  portions  of  food  being  kept  back  until  they  are  also  reduced 
into  chyme,  until  all  that  is  digestible  has  passed  out.  The  action  of 
these  fibres  is  often  seen  in  the  contracted  state  of  the  pyloric  portion  of 
the  stomach  after  death,  when  it  alone  is  contracted  and  firm,  while  the 
cardiac  portion  forms  a  dilated  sac.  Sometimes,  by  a  predominant  ac- 
tion of  strong  circular  fibres  placed  between  the  cardia  and  pylorus,  the 
two  portions,  or  ends  as  they  are  called,  of  the  stomach,  are  partially 
separated  from  each  other  by  a  kind  of  hour-glass  contraction.  By 
means  of  the  peristaltic  action  of  the  muscular  coats  of  the  stomach,  not 
merely  is  chymified  food  gradually  propelled  through  the  pylorus,  but  a 
kind  of  double  current  is  continually  kept  up  among  the  contents  of  the 
stomach,  the  circumferential  parts  of  the  mass  being  gradually  moved 
onward  towards  the  pylorus  by  the  contraction  of  the  muscular  fibres, 
while  the  central  portions  are  propelled  in  the  opposite  direction,  name- 
ly, towards  the  cardiac  orifice  ;  in  this  way  is  kept  up  a  constant  circu- 
lation of  the  contents  of  the  viscus,  highly  conducive  to  their  free 
mixture  with  the  gastric  fluid  and  to  their  ready  digestion. 

Influence  of  the  Nervous  System  on  Gastric  Digestion. — The 
normal  movements  of  the  stomach  during  gastric  digestion  are  directly 
connected  with  the  plexus  of  nerves  and  ganglia  contained  in  its  walls, 
the  presence  of  food  acting  as  a  stimulus  which  is  conveyed  to  the  gang- 
lia and  reflected  to  the  muscular  fibres.  Tne  stomach  is,  however  also 
directly  connected  with  the  higher  nerve-centres  by  means  of  branches 
of  the  vagus  and  solar  plexus  of  the  sympathetic.  The  vaso-motor 
fibres  of  the  latter  are  derived,  probably,  from  the  splanchnic  nerves. 

The  exact  function  of  the  vagi  in  connection  with  the  movements  of 
the  stomach  is  not  certainly  known.  Irritation  of  the  vagi  produces, 
contraction  of  the  stomach,  if  digestion  is  proceeding;  while,  on  the 
other  hand,  peristaltic  action  is  retarded  or  stopped,  when  these  nerves- 
are  divided. 

Bernard,  watching  the  act  of  gastric  digestion  in  dogs  which  had 
fistulous  openings  into  their  stomachs,  saw  that  on  the  instant  of  divid- 
ing their  vagi  nerves,  the  process  of  digestion  was  stopped,  and  the 
mucous  membrane  of  the  stomach,  previously  turgid  with  blood,  became 
pale,  and  ceased  to  secrete.  These  facts  may  be  explained  by  the  theory 
that  the  vagi  are  the  media  by  which,  during  digestion,  an  inhibitory 
impulse  is  conducted  to  the  vaso-motor  centre  in  the  medulla;  such  im- 
pulse being  reflected  along  the  splanchnic  nerves  to  the  blood-vessels  of 
the  stomach,  and  causing  their  dilatation  (Rutherford).  From  other 
experiments  it  may  be  gathered,  that  although  division  of  both  vagi 
always  temporarily  suspends  the  secretion  of  gastric  fluid,  and  so  arrests 


DIGESTION.  257 

the  process  of  digestion,  being  occasionally  followed  by  death  from  ina- 
nition; yet  the  digestive  powers  of  the  stomach  may  be  completely 
restored  after  the  operation,  and  the  formation  of  chyme  and  the  nutri- 
tion of  the  animal  may  be  carried  on  almost  as  perfectly  as  in  health. 
This  would  indicate  the  existence  of  a  special  local  nervous  mechanism 
which  controls  the  secretion. 

Bernard  found  that  galvanic  stimulus  of  these  nerves  excited  an 
active  secretion  of  the  fluid,  while  a  like  stimulus  applied  to  the  sympa- 
thetic nerves  issuing  from  the  semilunar  ganglia,  caused  a  diminution 
and  even  complete  arrest  of  the  secretion. 

The  influence  of  the  higher  nerve-centres  on  gastric  digestion,  as  in 
the  case  of  mental  emotion,  is  too  well  known  to  need  more  than  a 
reference. 

Digestion  of  the  Stomach  after  Death. — If  an  animal  die  during 
the  process  of  gastric  digestion,  and  when,  therefore,  a  quantity  of  gastric 
juice  is  present  in  the  interior  of  the  stomach,  the  walls  of  this  organ 
itself  are  frequently  themselves  acted  on  by  their  own  secretion,  and  to 
such  an  extent,  that  a  perforation  of  considerable  size  may  be  produced, 
and  the  contents  of  the  stomach  may  in  part  escape  into  the  cavity  of 
the  abdomen.  This  phenomenon  is  not  unfrequently  observed  in  post- 
mortem examinations  of  the  human  body.  If  a  rabbit  be  killed  during 
a  period  of  digestion,  and  afterwards  exposed  to  artificial  warmth  to  pre- 
vent its  temperature  from  falling,  not  only  the  stomach,  but  many  of 
the  surrounding  parts  will  be  found  to  have  been  dissolved  (Pavy). 

From  these  facts,  it  becomes  an  interesting  question  why,  during  life, 
the  stomach  is  free  from  liability  to  injury  from  a  secretion  which,  after 
death,  is  capable  of  such  destructive  effects? 

It  is  only  necessary  to  refer  to  the  idea  of  Bernard,  that  the  living 
stomach  finds  protection  from  its  secretion  in  the  presence  of  epithelium 
and  mucus,  which  are  constantly  renewed  in  the  same  degree  that  they 
are  constantly  dissolved,  in  order  to  remark  that,  although  the  gastric 
mucus  is  probably  protective,  this  theory,  so  far  as  the  epithelium  is 
concerned,  has  been  disproved  by  experiments  of  Pavy's,  in  which  the 
mucous  membrane  of  the  stomachs  of  dogs  was  dissected  off  for  a  small 
space,  and,  on  killing  the  animals  some  days  afterwards,  no  sign  of 
digestion  of  the  stomach  was  visible.  "  Upon  one  occasion,  after  remov- 
ing the  mucous  membrane,  and  exposing  the  muscular  fibres  over  a  space 
of  about  an  inch  and  a  half  in  diameter,  the  animal  was  allowed  to  live 
for  ten  days.  It  ate  food  every  day,  and  seemed  scarcely  affected  by  the 
operation.  Life  was  destroyed  whilst  digestion  was  being  carried  on, 
and  the  lesion  in  the  stomach  was  found  very  nearly  repaired;  new 
matter  had  been  deposited  in  the  place  of  what  had  been  removed,  and 
the  denuded  spot  had  contracted  to  much  less  than  its  original  dimen- 
sions." 

Pavy  believes  that  the  natural  alkalinity  of  the  blood,  which  circu- 
lates so  freely  during  life  in  the  walls  of  the  stomach,  is  sufficient  to 
neutralize  the  acidity  of  the  gastric  juice;  and  as  may  be  gathered  from 
what  has  been  previously  said,  the  neutralization  of  the  acidity  of  the 
gastric  secretion  is  quite  sufficient  to  destroy  its  digestive  powers;  but 
17 


258 


HANDBOOK    OF   PHYSIOLOGY. 


the  experiments  adduced  in  favor  of  this  theory  are  open  to  many  objec- 
tions, and  afford  only  a  negative  support  to  the  conclusions  they  are 
intended  to  prove.  Again,  the  pancreatic  secretion  acts  best  on  proteids 
in  an  alkaline  medium;  but  it  has  no  digestive  action  on  the  living  in- 


Fig.  189.  Auerbach's  nerve-plexus  in  small  intestine.  The  plexus  consists  of  fibrillated  sub- 
stance, and  is  made  up  of  trabeculse  of  various  thicknesses.  Nucleus-like  elements  and  ganglion- 
cells  are  imbedded  in  the  plexus,  the  whole  of  which  is  inclosed  in  a  nucleated  sheath.    (Klein.) 

testine.     It  must  be  confessed  that  no  entirely  satisfactory  theory  has 
been  yet  stated. 

Vomiting. 

The  expulsion  of  the  contents  of  the  stomach  in  vomiting,  like  that 
of  mucus  or  other  matter  from  the  lungs  in  coughing,  is  preceded  by  an 
inspiration;  the  glottis  is  then  closed,  and  immediately  afterwards  the 
abdominal  muscles  strongly  act;  but  here  occurs  the  difference  in  the 
two  actions.  Instead  of  the  vocal  cords  yielding  to  the  action  of  the 
abdominal  muscles,  they  remain  tightly  closed.  Thus  the  diaphragm 
being  unable  to  go  up,  forms  an  unyielding  surface  against  which  the 
stomach  can  be  pressed.  In  this  way,  as  well  as  by  its  own  contraction, 
the  diaphragm  is  fixed,  to  use  a  technical  phrase.  At  the  same  time  the 
cardiac  sphincter  muscle  being  relaxed,  and  the  orifice  which  it  naturally 
guards  being  actively  dilated,  while  the  pylorus  is  closed,  and  the 
stomach  itself  also  contracting,  the  action  of  the  abdominal  muscles,  by 
these  means  assisted,  expels  the  contents  of  the  organ  through  the 
oesophagus,  pharynx,  and  mouth.  The  reversed  peristaltic  action  of  the 
oesophagus  probably  increases  the  effect. 

It  has  been  frequently  stated  that  the  stomach  itself  is  quite  passive 
during  vomiting,  and  that  the  expulsion  of  its  contents  is  effected  solely 
by  the  pressure  exerted  upon  it  when  the  capacity  of  the  abdomen  is 


DIGESTION.  259 

diminished  by  the  contraction  of  the  diaphragm,  and  subsequently  of 
the  abdominal  muscles.  The  experiments  and  observations,  however, 
which  are  supposed  to  confirm  this  statement,  only  show  that  the  con- 
traction of  the  abdominal  muscles  alone  is  sufficient  to  expel  matters 
from  an  unresisting  bag  through  the  oesophagus;  and  that,  under  very 
abnormal  circumstances,  the  stomach,  by  itself,  cannot  expel  its  con- 
tents. They  by  no  means  show  that  in  ordinary  vomiting  the  stomach 
is  passive  ;  and,  on  the  other  hand,  there  are  good  reasons  for  believing 
the  contrary. 

It  is  true  that  the  facts  are  wanting  to  demonstrate  with  certainty 
this  action  of  the  stomach  in  vomiting;  but  some  of  the  cases  of  fistu- 
lous opening  into  the  organ  appear  to  support  the  belief  that  it  does  take 
place;  and  the  analogy  of  the  case  of  the  stomach  with  that  of  the  other 
hollow  viscera,  as  the  rectum  and  bladder,  may  be  also  cited  in  confirm- 
ation. 

The  muscles  concerned  in  the  act  of  vomiting  are  chiefly  and  prima- 
rily those  of  the  abdomen;  the  diaphragm  also  acts,  but  usually  not  as 
the  muscles  of  the  abdominal  walls  do.  They  contract  and  compress 
the  stomach  more  and  more  towards  the  diaphragm;  and  the  diaphragm 
(which  is  usually  drawn  down  in  the  deep  inspiration  that  precedes  each 
act  of  vomiting)  is  fixed,  and  presents  an  unyielding  surface  against 
which  the  stomach  may  be  pressed.  The  diaphragm  is,  therefore,  as  a 
rule  passive,  during  the  actual  expulsion  of  the  contents  of  the  stomach. 
But  there  are  grounds  for  believing  that  sometimes  this  muscle  actively 
contracts,  so  that  the  stomach  is,  so  to  speak,  squeezed  between  the  de- 
scending diaphragm  and  the  retracting  abdominal  walls. 

Some  persons  possess  the  power  of  vomiting  at  will,  without  applying 
any  undue  irritation  to  the  stomach,  but  simply  by  a  voluntary  effort. 
It  seems  also,  that  this  power  may  be  acquired  by  those  who  do  not  natu- 
rally possess  it,  and  by  continual  practice  may  become  a  habit.  There 
are  cases  also  of  rare  occurrence  in  which  persons  habitually  swallow  their 
food  hastily,  and  nearly  unmasticated,  and  then  at  their  leisure  regurgi- 
tate it,  piece  by  piece,  into  their  mouth,  remasticate,  and  again  swallow 
it,  like  members  of  the  ruminant  order  of  Mammalia. 

The  various  nerve-actions  concerned  in  vomiting  are  governed  by  a 
nerve-centre  situate  in  the  medulla  oblongata. 

The  sensory  nerves  are  the  fifth,  glosso-pharyngeal  and  vagus  prin- 
cipally; but,  as  well,  vomiting  may  occur  from  stimulation  of  sensory 
nerves  from  many  organs,  e.  g.,  kidney,  testicle,  etc.  The  centre  may 
also  be  stimulated  by  impressions  from  the  cerebrum  and  cerebellum, 
so  called  central  vomiting  occurring  in  disease  of  those  parts.  The 
efferent  impulses  are  carried  by  the  phrenics  and  other  spinal  nerves. 


260  HANDBOOK    OF   PHYSIOLOGY. 

The  Intestines. 

The  Intestinal  canal  is  divided  into  two  chief  portions,  named  from 
their  differences  in  diameter,  the  (I.)  small  and  (II.)  large  intestine 
(Fig.  164).  These  are  continuous  with  each  other,  and  communicate 
by  means  of  an  opening  guarded  by  a  valve,  the  ileo-cmcal  valve,  which 
allows  the  passage  of  the  products  of  digestion  from  the  small  into  the 
large  bowel,  but  not,  under  ordinary  circumstances,  in  the  opposite 
direction. 

I.  The  Small  Intestine. — The  Small  Intestine,  the  average  length 
of  which  in  an  adult  is  about  twenty  feet,  has  been  divided,  for  conveni- 
ence of  description,  into  three  portions,  viz.,  the  duodenum,  which 
extends  for  eight  or  ten  inches  beyond  the  pylorus;  the  jejunum,  which 
forms  two-fifths,  and  the  ileum,  which  forms  three-fifths  of  the  rest  of 
the  canal. 

Structure. — The  small  intestine,  like  the  stomach,  is  constructed  of 
four  principal  coats,  viz.,  the  serous,  muscular,  submucous,  and  mucous. 

(1. )  The  serous  coat,  formed  by  the  visceral  layer  of  the  peritoneum, 
and  has  the  structure  of  serous  membranes  in  general. 

(2.)  The  muscular  coats  consist  of  an  internal  circular  and  an  exter- 
nal longitudinal  layer;  the  former  is  usually  considerably  the  thicker. 
Both  alike  consist  of  bundles  of  unstriped  muscular  tissue  supported  by 
connective  tissue.  They  are  well  provided  with  lymphatic  vessels,  which 
form  a  set  distinct  from  those  of  the  mucous  membrane. 

Between  the  two  muscular  coats  is  a  nerve-plexus  ( Auerbach's  plexus, 
plexus  myentericus)  (Fig.  189),  similar  in  structure  to  Meissner's  (in  the 
submucous  tissue),  but  with  more  numerous  ganglia.  This  plexus  regu- 
lates the  peristaltic  movements  of  the  muscular  coats  of  the  intestines. 

(3.)  Between  the  mucous  and  muscular  coats  is  the  submucous  coat, 
which  consists  of  connective  tissue,  in  which  numerous  blood-vessels 
and  lymphatics  ramify.  A  fine  plexus,  consisting  mainly  of  non-medul- 
lated  nerve-fibres,  Meissner's  plexus,  with  ganglion  cells  at  its  nodes, 
occurs  in  the  submucous  tissue  from  the  stomach  to  the  anus.  From 
the  position  of  this  plexus  and  the  distribution  of  its  branches,  it  seems 
hig'niy  probable  that  it  is  the  local  centre  for  regulating  the  calibre  of 
the  blood-vessels  supplying  the  intestinal  mucous  membrane,  and  pre- 
siding over  the  processes  of  secretion  and  absorption. 

(4.)  The  mucous  membrane  is  the  most  important  coat  in  relation  to 
the  function  of  digestion.  The  following  structures,  which  enter  into 
its  composition,  may  now  be  successively  described: — the  valvular  conni- 
ventes;  the  villi;  and  the  glands.  The  general  structure  of  the  mucous 
membrane  of  the  intestines  resembles  that  of  the  stomach  (p.  245),  and, 
like  it,  is  lined  on  its  inner  surface  by  columnar  epithelium.  Adenoid 
tissue  (Fig.  100,  c  and  d)  enters  largely  into  its  construction;  and  on  its 


DIGESTION. 


261 


deep  surface  is  the  muscular  is  mucosce  (m  m,  Fig.  191),  the  fibres  of 
which  are  arranged  in  two  layers:  the  oirter  longitudinal  and  the  inner 
•circular. 

Valvules  Conniventes. — The  valvulse  conniventes(Fig.  192)  commence 
in  the  duodenum,  about  one  or  two  inches  beyond  the  pylorus,  and 
becoming  larger  and  more  numerous  immediately  beyond  the  entrance 
of  the  bile  duet,  continue  thickly  arranged  and  well  developed  through- 
out the  jejunum;  then,  gradually  diminishing  in  size  and  number,  they 
cease  near  the  middle  of  the  ileum.  They  are  formed  by  a  doubling 
inwards  of  the  mucous  membrane;  the  crescentic,  nearly  circular,  folds 
thus  formed  being  arranged  transversely  to  the  axis  of  the  intestine,  and 


Fig.  190.  Fig.  191. 

Fig.  190. — Horizontal  section  of  a  small  fragment  of  the  mucous  membrane,  including:  one  en- 
tire crypt  of  Lieberkuhn  and  parts  of  several  others;  a,  cavity  of  the  tubular  glands  or  crypts;  b, 
•one  of  the  lining  epithelial  cells;  c,  the  lymphoid  or  retiform  spaces,  o.  which  some  are  empty,  and 
others  occupied  by  lymph  cells,  as  at  d. 

Fig.  191.— Vertical  section  through  portion  of  small  intestine  of  dog.  t>,  two  villi  showing  e, 
epithelium;  g,  goblet  cells.  The  free  surface  is  seen  to  be  formed  by  the  "  striated  basilar  bonle r." 
while  inside  the  villus  the  adenoid  tissue  and  unstriped  muscle-cells  are  seen;  If.  Lieberkuhn's  folli- 
cles; to  to,  muscularis  mucosae,  sending  up  fibres  between  the  follicles  into  the  villi ;  sm,  submucous 
tissue;  containing  tgm),  ganglion  cells  of  Meissner's  plexus.    (.Schofleld  ) 

each  individual  fold  seldom  extending  around  more  than  ^  or  |-  of  the 
bowel's  circumference.  Unlike  the  rug*  in  the  cesophagus  and  stomach, 
they  do  not  disappear  on  distention  of  the  canal.  Only  an  imperfect 
notion  of  their  natural  position  and  function  can  be  obtained  by  looking 
at  them  after  the  intestine  has  been  laid  open  in  the  usual  manner.  To 
understand  them  aright,  a  piece  of  gut  should  be  distended  either  with 
air  or  alcohol,  and  not  opened  until  the  tissues  have  become  hardened. 


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HANDBOOK    OF    PHYSIOLOGY. 


On  then  making  a  section  it  will  be  seen  that,  instead  of  disappearing, 
they  stand  out  at  right  angles  to  the  general  surface  of  the  mucous 
membrane  (Fig.  192).  Their  functions  are  (1)  that  they  offer  a  largely 
increased  surface  for  secretion  and  absorption,  and  (2)  that  they  prevent 
the  too  rapid  passage  of  the  very  liquid  products  of  gastric  digest-ion, 
immediately  after  their  escape  from  the  stomach,  and  (3),  by  their  pro- 
jection, and  consequent  interference  with  an  uniform  and  untroubled 
current  of  the  intestinal  contents,  that  they  assist  in  the  more  perfect 
mingling  of  the  latter  with  the  secretions  poured  out  to  act  on  them. 

Glands. — The  glands  are  of  three  principal  kinds: — viz.,  those  of  (1) 
Lieberkiihn,  (2)  Brunner,  and  (3)  Peyer. 

(1.)  The  glands  or  crypts  of  Lieberkiihn  are  simple  tubular  depres- 
sions of  the  intestinal  mucous  membrane,  thickly  distributed  over  the 
whole  surface  both  of  the  large  and  small  intestines.  In  the  small  in- 
testine they  are  visible  only  with  the  aid  of  a  lens;  and  their  orifices  ap- 
pear as  minute  dots  scattered  between  the  villi.     They  are  larger  in  the 


Fig.  193. 


Fig.  194. 


Fig. 


Fig.  192. 
192 —piece  of  small  intestine  (previously  distended  and  hardened  by  alcohol)  laid   open 


to  show  the  normal  position  of  the  valvulse  conniventes. 

Fig.  193.— Transverse  section  through  four  crypts  of  Lieberkiihn  from  the  large  intestine  of  the 
pig.  They  are  lined  by  colummar  epithelial  cells,  the  nuclei  being  placed  in  the  outer  part  of  the 
cells.  The  divisions  between  the  cells  are  seen  as  lines  radiating  from  L,  the  lumen  of  the  crypt; 
G,  epithelial  cells,  which  have  become  transformed  into  goblet  cells.  X  350.  CKlein  and  Noble 
Smith.) 

Fig.  194.— A  frland  of  Lieberkiihn  in  longitudinal  section.     (Brmton.) 


large  intestine,  and  increase  in  size  the  nearer  they  approach  the  anal 
end  of  the  intestinal  tube;  and  in  the  rectum  their  orifices  may  be  vis- 
ible to  the  naked  eye.  In  length  they  vary  from  ¥V  to  TV  of  a  line. 
Each  tubule  (Fig.  194)  is  constructed  of  the  same  essential  parts  as  the 
intestinal  mucous  membrane,  viz.,  of  a  fine  membrana propria,  or  base- 
ment membrane,  a  layer  of  cylindrical  epithelium  lining  it,  and  capil- 
lary blood-vessels  covering  its  exterior,  the  free  surface  of  the  columnar 


DIGESTION.  263 

cells  presenting  an  appearance  precisely  similar  to  the  "  striated  basilar 
border"  which  covers  the  villi.  Their  contents  appear  to  vary,  even  in 
health;  the  varieties  being  dependent,  probably,  on  the  period  of  time 
in  relation  to  digestion  at  which  they  are  examined. 

Among  the  columnar  cells  of  Lieberkuhn's  follicles,  goblet  cells  fre- 
quently occur  (Fig.  193). 

(2.)  Brunner's  glands  (Fig.  106)  are  confined  to  the  duodenum;  they 
are  most  abundant  and  thickly  set  at  the  commencement  of  this  portion 
of  the  intestine,  diminishing  gradually  as  the  duodenum  advances.  They 
are  situated  beneath  the  mucous  membrane,  and  imbedded  in  the  sub- 
mucous tissue,  each  gland  is  a  branched  and  convoluted  tube,  lined  with 
columnar  epithelium.  As  before  said,  in  structure  they  are  very  similar 
to  the  pyloric  glands  of  the  stomach,  and  their  epithelium  undergoes  a 
similar  change  during  secretion;  but  they  are  more  branched  and  con- 
voluted and  their  ducts  are  longer.  (Watney.)  The  duct  of  each  gland 
passes  through  the  muscularis  mucosa?,  and  opens  on  the  surface  of  the 
mucous  membrane. 

(3.)  The  glands  of  Peyer  occur  chiefly  but  not  exclusively  in  the  small 
intestine.  They  are  found  in  greatest  abundance  in  the  lower  part  of 
the  ileum  near  to  the  ileo-csecal  valve.  They  are  met  with  in  two  condi- 
tions, viz.,  either  scattered  singly,  in  which  case  they  are  termed  glan- 
dules solitariw,  or  aggregated  in  groups  varying  from  one  to  three  inches 
in  length  and  about  half  an  inch  in  width,  chiefly  of  an  oval  form,  their 
long  axis  parallel  with  that  of  the  intestine.  In  this  state,  they  are 
named  glandulw  agminatcv,  the  groups  being  commonly  called  Peyer's 
patches  (Fig.  197),  and  almost  always  placed  opposite  the  attachment  of 
the  mesentery.  In  structure,  and  in  function,  there  is  no  essential  dif- 
ference between  the  solitary  glands  and  the  individual  bodies  of  which 
each  group  or  patch  is  made  up.  They  are  really  single  or  aggregated 
masses  of  adenoid  tissue  forming  lymph-follicles.  In  the  condition  in 
which  they  have  beeu  most  commonly  examined,  each  gland  appears  as 
a  circular  opaque-white  rounded  body,  from  -£T  to  T\  inch  in  diameter, 
according  to  the  degree  in  which  it  is  developed.  They  are  principally 
contained  in  the  submucous  coat,  but  sometimes  project  through  the 
muscularis  mucosa}  into  the  mucous  membrane.  In  the  agminate  glands, 
each  follicle  reaches  the  free  surface  of  the  intestine,  and  is  covered  with 
columnar  epithelium.  Each  gland  is  surrounded  by  the  openings  of 
Lieberkuhn's  follicles. 

The  adjacent  glands  of  a  Peyer's  patch  are  connected  together  by 
adenoid  tissue.  Sometimes  the  lymphoid  tissue  reaches  the  free  surface, 
replacing  the  epithelium,  as  is  also  the  case  with  some  of  the  lymphoid 
follicles  of  the  tonsil  (p.  242). 

Peyer's  glands  are  surrounded  by  lymphatic  sinuses  which  do  not 
penetrate  into  their  interior ;  the  interior  is,  however,  traversed  by  a 


264 


HANDBOOK    OF   PHYSIOLOGY. 


very  rich  blood  capillary  plexus.  If  the  vermiform  appendix  of  a  rabbit 
which  consists  largely  of  Peyer's  glands  be  injected  with  blue  by  press- 
ing the  point  of  a  fine  syringe  into  one  of  the  lymphatic  sinuses,  the 
Peyer's  glands  will  appear  as  grayish-white  spaces  surrounded  by  blue  ; 
if  now  the  arteries  of  the  same  be  injected  with  red,  the  grayish  patches 
will  change  to  red,  thus  proving  that  they  are  surrounded  by  lymphatic 
spaces  but  penetrated  by  blood-vessels.  The  lacteals  passing  out  of  the 
villi  communicate  with  the  lymph  sinuses  round  Peyer's  glands. 

It  is  to  'be  noted  that  they  are  largest  and  most  prominent  in 
children  and  young  persons. 

Villi.— The  Villi  (Figs.  191,   196,  198,  and  199),  are  confined  ex- 


Fig.  195.— Transverse  section  of  injected  Peyer's  glands  (from  Kolliker).  The  drawing  was 
taken  from  a  preparation  made  by  Frey:  it  represents  the  fine  capillary-looped  network  spreading 
from  the  surrounding  blood-vessels  into  the  interior  of  three  of  Peyer's  capsules  from  the  intestine 
of  the  rabbit. 

clusively  to  the  mucous  membrane  of  the  small  intestine.  They  are  mi- 
nute vascular  processes,  from  a  quarter  of  a  line  to  a  line  and  two-thirds 
in  length,  covering  the  surface  of  the  mucous  membrane,  and  giving  it 
a  peculiar  velvety,  fleecy  appearance.  Krause  estimates  them  at  fifty  to 
ninety  in  number  in  a  square  line  at  the  upper  part  of  the  small  intes- 
tine, and  at  forty  to  seventy  in  the  same  area  at  the  lower  part.  They 
vary  in  form  even  in  the  same  animal,  and  differ  according  as  the  lym- 
phatic vessels  they  contain  are  empty  or  full  of  chyle;  being  usually,  in 
the  former  case,  flat  and  pointed  at  their  summits,  in  the  latter  cylindri- 
cal or  cleavate. 

Each  villus  consists  of  a  small  projection  of  mucous  membrane,  and 
its  interior  is  therefore  supported  throughout  by  fine  adenoid  tissue, 
which  forms  the  framework  or  stroma  in  which  the  other  constituents 
are  contained. 


DIGESTION. 


265 


The  surface  of  the  villus  is  clothed  by  columnar  epithelium,  which 
rests  on  a  fine  basement  membrane;  while  within  this  are  found,  reck- 
oning from  without  inwards,  blood-vessels,  fibres  of  the  muscularis  mu- 
cosae, and  a  single  lymphatic  or  lacteal  vessel  rarely  looped  or  branched 
(Fig.  200);  besides  granular  matter,  fat-globules,  etc. 

The  epithelium  is  of  the  columnar 
kind,  and  continuous  with  that  lining  the 
other  parts  of  the  mucous  membrane. 
The  cells  are  arranged  with  their  long  axis 
radiating  from  the  surface  of  the  villus 
(Fig.  199),  and  their  smaller  ends  resting 
on  the  basement  membrane.  The  free 
surface  of  the  epithelial  cells  of  the  villi, 
like  that  of  the  cells  which  cover  the  gene- 
ral surface  of  the  mucous  membrane,  is 
covered  by  a  fine  border  which  exhibits 
very  delicate  striations,  whence  it  derives 
itsname,  "striated  basilar  border." 

Beneath  the  basement  or  limiting 
"membrane  there  is  a  rich  supply  of  blood- 
vessels. Two  or  more  minute  arteries  are 
distributed  within  each  villus  ;  and  from 
their  capillaries,  which  form  a  dense  net- 
work, proceed  one  or  two  small  veins, 
which  pass  out  at  the  base  of  the  villus. 

The  layer  of  the  muscularis  mucosa  in 
the  villus  forms  a  kind  of  thin  hollow  cone 
immediately  around  the  central  lacteal, 
and  is,  therefore,  situate  beneath  the  blood- 
vessels. It  is  without  doubt  instrumental 
in  the  propulsiou  of  chyle  along  the 
lacteal. 

The  lacteal  vessel  enters  the  base  of 
each  villus,  and  passing  up  in  the  mid- 
dle of  it,  extends  nearly  to  the  tip,  where  it  ends  commonly  by  a 
closed  and  somewhat  dilated  extremity.  In  the  larger  villi  there  may  be 
two  small  lacteal  vessels  which  end  by  a  loop  (Fig.  200),  or  the  lacteals 
may  form  a  kind  of  network  in  the  villus.  The  last  method  of  ending, 
however,  is  rarely  or  never  seen  in  the  human  subject,  although  common 
in  some  of  the  lower  animals  (a,  Fig.  201). 

The  office  of  the  villi  is  the  absorption  of  chyle  and  other  liquids  from 
the  intestine.  The  mode  in  which  they  effect  this  will  be  considered  in 
the  next  Chapter. 

II.  The  Large  Intestine. — The  Large  Intestine,  which  in  an  adult 


Fig.  196.— Vertical  section  of  duo- 
denum showing  o,  villi:  b  crypts  of 
Lieberkuhn,  and  c,  Bruuner's  glands 
in  the  submucosa  s.  with  ducts,  d; 
muscularis  mucosae,  m;  and  circular 
muscular  coat /.    ijSchofield.) 


2m 


HANDBOOK    OF    PHYSIOLOGY. 


is  from  about  4  to  6  feet  long,  is  subdivided  for  descriptive  purposes  into 
three  portions  (Fig.  164)  viz.  : — the  ccecum,  a  short  wide  pouch,  commu- 
nicatiag  with  the  lower  end  of  the  small  intestine  through  an  opening, 


Fig.  197.— Agminate  follicles,  or  Peyer's  patch,  in  the  state  of  distention,    x  5.    (Boehm.) 

guarded  by  the  ileo-cmcal  valve  ;  the  colon,  continuous  with  the  csecum, 
which  forms  the  principal  part  of  the  large  intestine,  and  is  divided  into 
ascending,  transverse,  and  descending  portions  ;  and  the  rectum,  which, 
after  dilating  at  its  lower  part,  again  contracts,  and  immediately  after- 


Fig.  198. 


Fig.  199. 


Fig.  198.— Section  of  small  intestine,  showing  villi,  Lieberkiihn's  glands  and  a  Peyer's  solitary 
gland,    w,  m,  muscularis  mucosas     (Klein  and  Noble  Smith.) 

Fig.  199.— Vertical  section  of  a  villus  of  the  small  intestine  of  a  cat.  a,  striated  basilar  border 
of  the  epithelium;  6,  columnar  epithelium;  c,  goblet  cells;  d,  central  lymph-vessel;  e,  smooth 
muscular  fibres;  /,  adenoid  stroma  of  the  villus  in  which  lymph  corpuscles  lie.     (Klein.) 

wards  opens  externally  through  the  anus.     Attached  to  the  caecum  is  the 
small  appendix  vermiformis. 

Structure. — Like  the  small  intestine,  the  large  intestine  is  constructed 
of  four  principal  coats,  viz.,  the  serous,  muscular,  submucous,  and  mu- 
cous. The  serous  coat  need  not  be  here  particularly  described.  Con- 
nected with  it  are  the  small  processes  of  peritoneum   containing  fat, 


DIGESTION. 


267 


called  appendices  epiploic*.?.  The  fibres  of  the  muscular  coat,  like  those 
of  the  small  intestine,  are  arranged  in  two  layers— the  outer  longitudinal, 
the  inner  circular.  In  the  caecum  and  colon,  the  longitudinal  fibres,  be- 
sides being,  as  in  the  small  intestine,  thinly  disposed  in  all  parts  of  the 
wall  of  the  bowel,  are  collected,  for  the  most  part,  into  three  strong 
bands,  which,  being  shorter,  from  end  to  end,  than  the  other  coats  of  the 
intestine,  hold  the  canal  in  folds,  bounding  intermediate  sacculi.  On 
the  division  of  these  bands,  the  intestine  can  be  drawn  out  to  its  full 
length,  and  it  then  assumes,  of  course,  an  uniformly  cylindrical  form. 
In  the  rectum,  the  fasciculi  of  these  longitudinal  bands  spread  out  and 


Fig.  200.— A.    Villus  of  sheep.    B.  Villi  of  man.    (Slightly  altered  from  TeichmaniO 

mingle  with  the  other  longitudinal  fibres,  forming  with  them  a  thicker 
layer  of  fibres  than  exists  on  any  other  part  of  the  intestinal  canal.  The 
circular  muscular  fibres  are  spread  over  the  whole  surface  of  the  bowel, 
but  are  somewhat  more  marked  in  the  intervals  between  the  sacculi. 
Towards  the  lower  end  of  the  rectum  they  become  more  numerous,  and 
at  the  anus  they  form  a  strong  band  called  the  internal  sphincter  muscle. 
The  mucous  membrane  of  the  large,  like  that  of  the  small  iutestine, 
is  lined  throughout  by  columnar  epithelium,  but,  unlike  it,  is  quite 
smooth  and  destitute  of  villi,  and  is  not  projected  in  the  form  of  valvula 
conniventes.  Its  general  microscopic  structure  resembles  that  of  the 
small  intestine  :  and  it  is  bounded  below  by  the  muscular  is  mucosa. 


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HANDBOOK    OF    PHYSIOLOGY. 


The  general  arrangement  of  ganglia  and  nerve-fibres  in  the  large  in- 
testine resembles  that  in  the  small  (p.  260). 

Glands. — The  glands  with  which  the  large  intestine  is  provided  are 
of  two  kinds,  (1)  the  tubular  and  (2)  the  lymphoid. 

(1. )  The  tubular  glands,  or  glands  of  Lieberkiihn,  resemble  those  of 
the  small  intestine,  but  are  somewhat  larger  and  more  numerous.  They 
are  also  more  uniformly  distributed. 

(2.)  Follicles  of  adenoid  or  lymphoid  tissue  are  most  numerous  in  the 
cascum  and  vermiform  appendix.     They  resemble  in  shape  and  structure, 


Fig.  201.— Diagram  of  lacteal  vessels  in  small  intestine,  a,  lacteals  in  villi;  p,  Peyer's  glands; 
b  and  d,  superficial  and  deep  network  of  lacteals  in  submucous  tissue ;  l,  Lieberkuhn's  glands:  e, 
small  branch  of  lacteal  vessel  on  its  way  to  mesenteric  gland;  h  and  o,  muscular  fibres  of  intes- 
tine; s,  peritoneum.    (Teichmann.) 

almost  exactly,  the  solitary  glands  of  the  small  intestine.     Peyer's  patches 
are  not  found  in  the  large  intestine. 

Ileo-caecal  Valve. — The  ileo-caecal  valve  is  situate  at  the  place  of 
junction  of  the  small  with  the  large  intestine,  and  guards  against  any  re- 
flux of  the  contents  of  the  latter  into  the  ileum.  It  is  composed  of  two 
semilunar  folds  of  mucous  membrane.  Each  fold  is  formed  by  a  dou- 
bling inwards  of  the  mucous  membrane,  and  is  strengthened  on  the  out- 
side by  some  of  the  circular  muscular  fibres  of  the  intestine,  which  are 
contained  between  the  outer  surfaces  of  the  two  layers  of  which  each  fold 
is  composed.     While  the  circular  muscular  fibres,  however,  of  the  bowel 


DIGESTION. 


260 


at  the  junction  of  the  ileum  with  the  caecum  are  contained  between  the 
outer  opposed  surfaces  of  the  folds  of  mucous  membrane  which  form  the 
valve,  the  longitudinal  muscular  fibres  and  the  peritoneum  of  the  small 
and  large  intestine  respectively  are  continuous  with  each  other,  without 


Fig.  202.— Horizontal  section  through  a  portion  of  the  mucous  membrane  of  the  large  intes- 
tine, showing  LieberkiUm'ls  glands  in  transverse  section,  a,  lumen  of  gland— lining  of  columnar 
cells  with  c,  goblet  cells,  b,  supporting  connective  tissue.    Highly  magnified.     (V.  D.  Harris.  > 

dipping  in  to  follow  the  circular  fibres  and  the  mucous  membrane.  In 
this  manner,  therefore,  the  folding  inwards  of  these  two  last-named 
structures  is  preserved,  while  on  the  other  hand,  by  dividiug  the  longitu- 
dinal muscular  fibres  and  the  peritoneum,  the  valve  can  be  made  to  dis- 
appear, just  as  the  constrictions  between  the  sacculi  of  the  large  intestine 
can  be  made  to  disappear  by  performing  a  similar  operation.  The  inner 
surface  of  the  folds  is  smooth  :  the  mucous  membrane  of  the  ileum  being 
continuous  with  that  of  the  caecum.  That  surface  of  each  fold  which 
looks  towards  the  small  intestine  is  covered  with  villi,  while  that  which 
looks  to  the  caecum  has  none.  When  the  caecum  is  distended,  the 
margins  of  the  folds  are  stretched,  and  thus  are  brought  into  firm  apposi- 
tion one  with  the  other. 


Digestion  in  the  Intestines. 

After  the  food  has  been  duly  acted  upon  by  the  stomach,  such  as  has 
not  been  absorbed  passes  into  the  duodenum,  and  is  there  subjected  to 
the  action  of  the  secretions  of  the  pancreas  and  liver  which  enter  that 
portion  of  the  small  intestine.  Before  considering  the  changes  which 
the  food  undergoes  in  consequence,  attention  should  be  directed  to  the 


270 


HANDBOOK    OF    PHYSIOLOGY. 


structure  and  secretion  of  these  glands,  and  to  the  secretion  (succus 
entericus)  which  is  poured  out  into  the  intestines  from  the  glands  lining 
them. 

The  Pancreas,  and  its  Secretion. 

The  Pancreas  is  situated  within  the  curve  formed  by  the  duode- 
num; and  its  main  duct  opens  into  that  part  of  the  small  intestine, 
through  a  small  opening,  or  through  a  duct  common  to  it  and  to  the 
liver,  about  two  and  a  half  inches  from  the  pylorus. 

Structure. — In  structure  the  pancreas  bears  some  resemblance  to  the 
salivary  glands.  Its  capsule  and  septa,  as  well  as  the  blood-vessels  and 
lymphatics,  are  similarly  distributed.  It  is,  however,  looser  and  softer, 
the  lobes  and  lobules  being  less  compactly  arranged.     The  main  duct 


Fig.  203.— Section  of  the  pancreas  of  a  dog  during  digestion,  a,  alveoli  lined  with  cells,  the 
outer  zone  of  which  is  well  stained  with  hasmatoxylin ;  d,  intermediary  duct  lined  with  squamous 
epithelium,     x  350.    (Klein  and  Noble  Smith.) 

divides  into  branches  (lobar  ducts),  one  for  each  lobe,  and  these  branches 
subdivide  into  intralobular  ducts,  and  these  again  by  their  division  and 
branching  form  the  gland  tissue  proper.  The  intralobular  ducts  corre- 
spond to  a  lobule,  while  between  them  and  the  secreting  tubes  or  alveoli 
are  longer  or  shorter  intermediary  ducts.  The  larger  ducts  possess  a 
very  distinct  lumen  and  a  membraua  propria  lined  with  columnar  epi- 
thelium, the  cells  of  which  are  longitudinally  striated,  but  are  shorter 
than  those  found  in  the  ducts  of  the  salivary  glands.  In  the  intralobu- 
lar ducts  the  epithelium  is  short  and  the  lumen  is  smaller.  The  inter- 
mediary ducts  opening  into  the  alveoli  possess  a  distinct  lumen,  with  a 
membrana  propia  lined  with  a  single  layer  of  flattened  elongated  cells. 
The  alveoli  are  branched  and  convoluted  tubes,  with  a  membrana  pro- 
pria lined  with  a  single  layer  of  columnar  cells.  They  have  no  distinct 
lumen,  the  centre  portion  of  the  tube  being  occupied  by  fusiform  or 
branched  cells.     Heidenhain   has    observed  that   the  alveolar  cells   in 


DIGESTION'.  271 

the  pancreas  of  a  fasting  dog  consist  of  two  zones,  an  inner  or  central 
zone  which  is  finely  granular,  and  which  stains  feebly,  and  a  smaller 
parietal  zone  of  finely  striated  protoplasm  which  stains  easily.  The 
nucleus  is  partly  in  one,  partly  in  the  other  zone.  During  digestion,  it 
is  found  that  the  outer  zone  increases  in  size,  and  the  central  zone 
diminishes  ;  the  cell  itself  becoming  smaller  from  the  discharge  of  the 
secretion.  At  the  end  of  digestion  the  first  condition  again  appears,  the 
inner  zone  enlarging  at  the  expense  of  the  outer.  It  appears  that  the 
granules  are  formed  by  the  protoplasm  of  the  cells,  from  material  sup- 
plied to  it  by  the  blood.  The  grannies  are  thought  to  be  not  the  fer- 
ment itself,  but  material  from  which,  under  certain  conditions,  the  fer- 
ments of  the  gland  are  made,  and  therefore  called  Zymogen.  The 
special  form  of  nerve  terminations,  called  Pacinian  corpuscles,  are  often 
found  in  the  pancreas. 

Pancreatic  Secretion. — The  secretion  of  the  pancreas  has  been  ob- 
tained for  purposes  of  experiment  from  the  lower  animals,  especially  the 
dog,  by  opening  the  abdomen  and  exposing  the  duct  of  the  gland,  which 
is  then  made  to  communicate  with  the  exterior.  A  pancreatic  fistula 
is  thus  established. 

An  extract  of  pancreas  made  from  the  gland  which  has  been  re- 
moved from  an  animal  killed  during  digestion  possesses  the  active  prop- 
erties of  pancreatic  secretion.  It  is  made  by  first  dehydrating  the  gland, 
which  has  been  cut  up  into  small  pieces,  by  keeping  it  for  some  days  in 
absolute  alcohol,  and  then,  after  the  entire  removal  of  the  alcohol,  plac- 
ing it  in  strong  glycerin.  A  glycerin  extract  is  thus  obtained.  It  is  a 
remarkable  fact,  however,  that  the  amount  of  the  ferment  trypsin 
greatly  increases  if  the  gland  be  exposed  to  the  air  for  twenty-four  hours 
before  placing  in  alcohol;  indeed,  a  glycerin  extract  made  from  the 
gland  immediately  upon  removal  from  the  body  often  appears  to  contain 
none  of  the  ferment.  This  seems  to  indicate  that  the  conversion  of 
zymogen  in  the  gland  into  the  ferment  only  takes  place  during  the  act 
of  secretion,  and  that  the  gland,  although  it  always  contains  in  its  cells 
the  materials  (trypsinogen)  out  of  which  trypsin  is  formed,  yet  the  con- 
version of  the  one  into  the  other  only  takes  place  by  degrees.  Dilute 
acid  appears  to  assist  and  accelerate  the  conversion,  and  if  a  recent  pan- 
creas be  rubbed  up  with  dilute  acid,  before  deyhdration,  a  glycerin 
extract  made  afterwards,  even  though  the  gland  may  have  been  oulv  re- 
cently removed  from  the  body,  is  very  active. 

Properties. — Pancreatic  juice  is  colorless,  transparent,  and  slightly 
viscid,  alkaline  in  reaction.  It  varies  in  specific  gravity  from  1010  to 
1015,  according  as  it  is  obtained  from  a  permanent  fistula — then  more 
watery — or  from  a  newly-opened  duct.  The  solids  vary  in  a  temporary 
.fistula  from  80  to  100  parts  per  thousand,  and  in  a  permanent  one  from 
16  to  50  per  thousand. 


272  HANDBOOK    OF    PHYSIOLOGY. 

Chemical  Composition  of  the  Pancreatic  Secretion. 

From  a  permanent  fistula.     (Bernstein.) 

Water,       ........       975 

Solids — Ferments    (including  trypsin,  amylop- 

sin,  rennet,  and  ?  steapsin): 
Proteids,   including   Serum- Albumin  ) 

and  Casein,    .         .         .         .         .  >    17 
Leucin  and  Tyrosin;  Fats  and  Soaps.  ) 
Inorganic  residue,  especially  Sodium  )       8 

Carbonate, ) 25 


1000 


Functions. — (1.)  By  the  aid  of  its  proteolytic  ferment  trypsin,  it 
converts  proteids  into  peptones,  the  intermediate  product  being  not  akin 
to  syntonin  or  acid-albumin  as  in  gastric  digestion,  but  to  alkali-albu- 
min. Kuhne  calls  the  intermediate  products,  both  in  the  peptic  and 
pancreatic  digestion  of  proteids,  anti-albumose  and  hemi-albumose,  and 
states  that  the  peptones  formed  correspond  to  these  products,  which  he 
therefore  terms  anti-peptone  and  lieyni-peptone.  The  hemipeptone  is 
capable  of  being  converted  by  the  action  of  the  pancreatic  ferment  — 
trypsin— \x\to  leucin  or  amido-caproic  acid  (C6H12N~05)  and  tyrosin 
(C^H^jNTOJ,  but  is  not  so  changed  by  pepsin:  the  antipeptone  cannot 
be  further  split  up.  The  products  of  pancreatic  digestion  are  sometimes 
further  complicated  by  the  appearance  of  certain  fsecal  substances  of 
which  indol  (C3HJS"),  sh  itol  (C9HUN"),  phenol  (C6H60),  and  napthila- 
mine  are  the  most  important.     (Kiihne  ) 

When  the  digestion  goes  on  for  a  long  time  the  indol  is  formed  in 
considerable  quantities,  and  emits  a  most  disagreeable  fsecal  odor.  These 
further  products  are  produced  by  the  presence  of  numerous  micro-organ- 
isms in  the  pancreatic  digestion  fluid. 

All  the  albuminous  or  proteid  substances  which  have  not  been  con- 
verted into  peptone  and  absorbed  in  the  stomach,  and  the  partially 
changed  substances,  i  e.,  the  para-peptones,  are  converted  into  peptone 
by  the  pancreatic  juice,  and  then  in  part  into  leucin  and  tyrosin. 

(2.)  The  action  of  the  pancreatic  juice  upon  the  gelatins,  or  nitrog- 
enous bodies  other  than  proteids,  is  not  so  distinct.  Mucin  can,  however, 
be  dissolved,  but  not  keratin  in  horny  tissues.  Gelatin  itself  is  formed 
into  peptone  (gelati?i-peptone). 

(3  )  Starch  is  converted  into  maltose  and  then  into  glucose  in  an  ex- 
actly similar  manner  to  that  which  happens  with  the  saliva;  erythro-and 
achroo-dextrine  being  intermediate  products.  If  the  sugar  which  is  at 
first  formed  is  maltose,  the  ferment  of  the  pancreatic  juice  after  a  time 
completes  the  whole  change  of  starch  into  glucose.     This  distinct  amy- 


DIGESTION.  273 

lolytic  ferment  in  the  pancreatic  juice  which  cannot  be  distinguished 
from  ptyalin,  is  called  Amylopsin. 

(4.)  Pancreatic  juice  possesses  the  property  of  curdling  milk,  contain- 
ing a  special  (rennet)  ferment  for  that  purpose.  The  ferment  is  distinct 
from  trypsin,  and  will  act  in  the  presence  of  an  acid  (W.  Roberts).  It 
is  best  extracted  by  brine. 

(5.)  Oils  and  fats  are  emulsified  and  saponified  by  pancreatic  secre- 
tion. The  terms  emulsification  and  saponification  may  need  a  little  ex- 
planation. The  former  is  used  to  signify  an  important  mechanical 
change  in  oils  or  fats,  whereby  they  are  made  into  an  emulsion,  or  in 
other  words  are  minutely  subdivided  into  small  particles.  If  a  small 
drop  of  an  emulsion  be  looked  at  under  the  microscope  it  will  be  seen  to 
be  made  up  of  an  immense  number  of  minute  rounded  particles  of  oil 
or  fat,  of  varying  sizes.  The  more  complete  the  emulsion  the  smaller 
are  these  particles.  An  emulsion  is  formed  at  once  if  oil  or  fat,  which 
nearly  always  is  slightly  acid  from  the  presence  of  free  fatty  acid,  is 
mixed  with  an  alkaline  solution.  Saponification  signifies  a  distinct 
chemical  change  in  the  composition  of  oils  and  fats.  An  oil  or  a  fat  is 
made  up  chemically  of  glycerin,  a  triatomic  alcohol  (see  Appendix),  and 
one  or  more  fatty  acid  radicles.  When  an  alkali  is  added  to  a  fat  and 
heat  is  applied,  two  changes  take  place,  firstly,  the  oil  or  fat  is  split  up 
into  glycerin  and  its  corresponding  fatty  acid;  secondly,  the  fatty  acid 
combines  with  the  alkali  to  form  a  soap  which  is  chemically  known  as 
stearate,  oleate,  or  palmitate  of  potassium  or  sodium.  Thus  saponifica- 
tion means  a  chemical  splitting  up  of  oils  or  fats  into  new  compounds, 
and  emulsification  means  merely  a  mechanical  splitting  of  them  up  into 
minute  particles.  The  pancreatic  juice  has  been  for  many  years  credited 
with  the  possession  of  a  special  ferment,  which  was  called  by  Claude 
Bernard  steapsin,  and  which  was  supposed  to  aid  in  one  or  both  of  these 
processes.  It  appears  very  doubtful,  however,  if  either  the  mechanical 
or  the  chemical  splitting  up  of  fats  by  the  alkaline  pancreatic  juice  is  a 
ferment  action  at  all. 

Several  cases  have  been  recorded  in  which  the  pancreatic  duct  being 
obstructed,  so  that  its  secretion  could  not  be  discharged,  fatty  or  oily 
matter  was  abundantly  discharged  from  the  intestines.  In  nearly  all 
these  cases,  indeed,  the  liver  was  coincidentally  diseased,  and  the  change 
or  absence  of  the  bile  might  appear  to  contribute  to  the  result,  yet  the 
frequency  of  extensive  disease  of  the  liver,  unaccompanied  by  fatty  dis- 
charges from  the  intestines,  favors  the  view  that,  in  these  cases,  it  is  to 
the  absence  of  the  pancreatic  fluid  from  the  intestines  that  the  excretion 
or  non-absorption  of  fatty  matter  should  be  ascribed. 

Conditions  favorable  to  the  Action. — These  are  similar  to  those 
which  are  favorable  to  the  action  of  the  saliva,  and  the  reverse  (p.  235). 

is 


27tt  HANDBOOK    OF    PHYSIOLOGY^ 

The  Liver. 

The  Liver,  the  largest  gland  in  the  body,  situated  in  the  abdomen  on 
the  right  side  chiefly,  is  an  extremely  vascular  organ,  and  receives  its  sup- 
ply of  blood  from  two  distinct  sources,  viz.,  from  the  portal  vein. and  from 
the  hepatic  artery,  while  the  blood  is  returned  from  it  into  the  vena  cava 
inferior  by  the  hepatic  veins.  Its  secretion,  the  bile,  is  conveyed  from  it 
by  the  hepatic  duct,  either  directly  into  the  intestine,  or,  when  digestion 
is  not  going  on,  into  the  cystic  duct,  and  thence  into  the  gall-bladder, 
where  it  accumulates  until  required.  The  portal  vein,  hepatic  artery, 
and  hepatic  duct  branch  together  throughout  the  liver,  while  the  hepatic 
veins  and  their  tributaries  run  by  themselves. 

On  the  outside,  the  liver  has  an  incomplete  covering  of  peritoneum, 
and  beneath  this  is  a  very  fine  coat  of  areolar  tissue,  continuous  over  the 


Fig.  204.— The  under  surface  of  the  liver,  a.  b.,  gall-bladder;  h.  d.,  common  bile-duct;  h.  a., 
hepatic  artery;  v.  p.,  portal  vein;  l.  q.,  lobulus  quadratus;  l,.  s.,  lobulus  spigelii;  l.  c,  lobulus 
caudatus;  d.  v.,  ductus  venosus;  u.  v.,  umbilical  vein.    (Noble  Smith.) 

whole  surface  of  the  organ.  It  is  thickest  when  the  peritoneum  is  ab- 
sent, and  is  continuous  on  the  general  surface  of  the  liver  with  the  fine 
and,  in  the  human  subject,  almost  imperceptible  areolar  tissue  investing 
the  lobules.  At  the  transverse  fissure  it  is  merged  in  the  areolar  invest- 
ment called  Glisson's  capsule,  which,  surrounding  the  portal  vein,  he- 
patic artery,  and  hepatic  duct,  as  they  enter  at  this  part,  accompanies 
them  in  their  branchings  through  the  substance  of  the  liver. 

Structure. — The  liver  is  made  up  of  small  roundish  or  oval  portions 
called  lobules,  each  of  which  is  about  TV  of  an  inch  in  diameter,  and 
composed  of  the  minute  branches  of  the  portal  vein,  hepatic  artery,  he- 
patic duct,  and  hepatic  vein;  while  the  interstices  of  these  vessels  are 
filled  by  the  liver  cells.  The  hepatic  cells  (Fig.  205),  which  form  the 
glandular  or  secreting  part  of  the  liver,  are  of  a  spheroidal  form,  some- 
what polygonal  from  mutual  pressure,  about  -^-to  y^o"  inCft  m  diameter, 
possessing  one,  sometimes  two  nuclei.     The  cell-substance  contains  nu- 


DIGESTION. 


275 


merous  fatty  molecules,  and  some  yellowish-brown  granules  of  bile-pig- 
ment. The  cells  sometimes  exhibit  slow  amoeboid  movements.  They 
are  heid  together  by  a  very  delicate  sustentacular  tissue,  continuous  with 
the  interlobular  connective  tissue. 

To  understand  the  distribution  of  the  blood-vessels  in  the  liver,  it 
will  be  well  to  trace,  first,  the  two  blood-vessels  and  the  duct  which  en- 
ter the  organ  on  the  under  surface  at  the  transverse  fissure,  viz  ,  the 
portal  vein,  hepatic  artery,  and  hepatic  duct.  As  before  remarked,  all 
three  run  in  company,  and  their  appearance  on  longitudinal  section  is 
shown  in  Fig.  206.  Eunning  together  through  the  substance  of  the 
liver,  they  are  contained  in  small  channels  called  portal  canals,  their 
immediate  investment  being  a  sheath  of  areolar  tissue  (Glisson's  capsule). 

d    a 


Fig.  305. 


Fig.  206. 


Fig.  205.— A.  Liver-cells.    B.  Ditto,  containing  various-sized  particles  of  fat. 

Fig.  206.— Longitudinal  section  of  a  portal  canal,  containing  a  portal  vein,  hepatic  artery  and 
hepatic  duct,  from  the  pig.  p,  hranch  of  vena  portse,  situate  in  a  portal  canal  formed  amongst  the 
lobules  of  the  liver,  1 1,  and  giving  off  vaginal  branches;  there  are  also  seen  within  the  large  portal 
vein  numerous  orifices  of  the  smallest  interlobular  veins  arising  directly  from  it ;  a,  hepatic  artery; 
b,  hepatic  duct.    X  5.    (^Kiernan.) 


To  take  the  distribution  of  the  portal  vein  first  : — In  its  course 
through  the  liver  this  vessel  gives  off  small  branches  which  divide  and 
and  subdivide  between  the  lobules  surrounding  them  and  limiting  them, 
and  from  this  circumstance  called  inter-\ohx\\-&v  veins.  From  these  small 
vessels  a  dense  capillary  network  is  prolonged  into  the  substance  of  the 
lobule,  and  this  network  gradually  gathering  itself  up,  so  to  speak,  into 
larger  vessels,  converges  finally  to  a  single  small  vein,  occupying  the 
centre  of  the  lobule,  and  hence  called  intra-lohul&T.  This  arrangement 
is  well  seen  in  Fig.  207,  which  represents  a  transverse  section  of  a  lobule. 

The  small  <Wra-lobular  veins  discharge  their  contents   into   veins 


276 


HANDBOOK    OF  PHYSIOLOGY. 


called  sz^-lobular  (h  h  h,  Fig.  208);  while  these  again,  by  their  union,, 
form  the  main  branches  of  the  hepatic  veins,  which  leave  the  posterior 
border  of  the  liver  to  end  by  two  or  three  principal  trunks  in  the  infe- 


%&. 


Fig.  207.  Cross  section  of  a  lobule  of  the  human  liver,  in  which  the  capillary  network  between 
the  portal  and  hepatic  veins  has  been  fully  injected  1 ,  section  of  the  intra  -lobular  vein ;  2,  its  smaller 
branches  collecting  blood  from  the  capillary  network;  3,  inter-lobular  branches  of  the  vena 
porta?  with  their  smaller  ramifications  passing  inwards  towards  the  capillary  network  in  the  sub- 
stance of  the  lobule,    x  60.    CSappey.) 


Fio.  208.— Section  of  a  portion  of  liver  passing  longitudinally  through  a  considerable  hepatic 
vein,  from  the  pig.  h.  hepatic  venous  trunk,  against  which  the  sides  of  the  lobules  (I)  are  applied  : 
h,  h,  h,  sublobular  hepatic  veins,  on  which  the  bases  of  the  lobules  rest,  and  through  the  coats  or 
which  they  are  seen  as  polygonal  figures  ;  i,  mouth  of  the  intralobular  veins,  opening  into  the 
sublobular  veins  ;  i',  intralobular  veins  shown  passing  up  the  centre  of  some  divided  lobules  ;  I,  I, 
cut  surface  of  the  liver  ;  c,  c,  walls  of  the  hepatic  venous  canal,  formed  by  the  polygonal  bases  of 
the  lobules.     /,  5      CKiernan.^i 


DIGESTION. 


277 


rior  "vena  cava,  just  before  its  passage  through  the  diaphragm.  The 
sw£-lobular  and  hepatic  veins,  unlike  the  portal  vein  and  its  companions, 
have  little  or  no  areolar  tissue  around  them,  and  their  coats  being  very 
thin,  they  form  little  more  than  mere  channels  in  the  liver  substance 
which  closely  surrounds  them. 

The  manner  in  which  the  lobules  are  connected  with  the  sv.blobular 
veins  by  means  of  the  small  intralobular  veins  is  well  seen  in  the  diagram 
(Fig.  209  and  in  Fig.  2C8),  which  represent  the  parts  as  seen  in  a  longi- 
tudinal section.  The  appearance  has  been  likened  to  a  twig  having 
leaves  without  footstalks — the  lobules  representing  the  leaves,  and  the 
sublobular  vein  the  small  branch  from  which  it  springs.  On  a  trans- 
verse section,  the  appearance  of  the  intralobular  veins  is  that  of  1,  Fig. 
207,  while  both  a  transverse  and  longitudinal  section  are  exhibited  in 
Fig.  208. 

The  hepatic  artery,  the  function  of  which  is  to  distribute  blood  for 


\ 


LoliulcM 


Lobuleu 


Fig.  2C9. 


Fig.  210. 


Fig.  209.— Diagram  showing  the  manner  in  which  the  lobules  of  the  liver  rest  on  the  sublobular 
Teins.    (After  Kiernan. ) 

Fig.  210.  -  Capillary  network  of  the  lobules  of  the  rabbit's  liver.  The  figure  is  taken  from  a  very- 
successful  injection  of  the  hepatic  veins,  made  by  Harting  ;  it  shows  nearly  the  whole  of  two 
lobules,  and  parts  of  three  otners  ;  p,  portal  branches  running  in  the  interlobular  spaces  ;  h, 
hepatic  veins  penetrating  and  radiating  from  the  centre  of  the  lobules.     X  45.     (Kolliker.) 


nutrition  to  GHisson's  capsule,  the  walls  of  the  ducts  and  blood-vessels, 
and  other  parts  of  the  liver,  is  distributed  in  a  very  similar  manner  to 
the  portal  vein,  its  blood  being  returned  by  small  branches  either  into 
the  ramifications  of  the  portal  vein,  or  into  the  capillary  plexus  of  the 
lobules  which  connects  the  inter-  and  iutra-\obu\nr  veins. 

The  hepatic  duct  divides  and  subdivides  in  a  manner  very  like  that 
of  the  portal  vein  and  hepatic  artery,  the  larger  branches  being  lined  by 
■cylindrical,  and  the  smaller  by  small  polygonal  epithelium. 

The  bile-capillaries  commence  between  the  hepatic  cells,  and  are 
bounded  by  a  delicate  membranous  wall  of  their  own.     They  appear  to 


278 


HANDBOOK    OF    PHYSIOLOGY. 


be  always  bounded  by  hepatic  cells  on  all  sides,  and  are  thus  separated 
from  the  nearest  blood-capillary  by  at  least  the  breadth  of  one  cell  (Figs. 
211  and  212). 

The  Gall-bladder. 

The  Gall-bladder  (g,  b,  Fig.  204)  is  a  pyriform  bag,  attached  to 
the  under  surface  of  the  liver,  and  supported  also  by  the  peritoneum, 
•which  passes  below  it.  The  larger  end  or  fundus,  projects  beyond  the 
front  margin  of  the  liver ;  while  the  smaller  end  contracts  into  the 
cystic  duct. 

Structure. — The  walls  of  the  gall-bladder  are  constructed  of  three 
principal  coats.  (1)  Externally  (excepting  that  part  which  is  in  con- 
tact with  the  liver),  is  the  serous  coat,  which  has  the  same  structure  as 


Fig.  211. 


Fig.  212. 


Fig.  211.— Portion  of  a  lobule  of  liver,  a,  bile  capillaries  between  liver-cells,  the  network  in 
which  is  well  seen  ;  b,  blood  capillaries,     x  350.     (Klein  and  Noble  Smith.) 

Fig.  212.— Hepatic  cells  and  bile  capillaries,  from  the  liver  of  a  child  three  months  old.  Both 
figures  represent  fragments  of  a  section  carried  through  the  periphery  of  a  lobule.  The  red  cor- 
puscles of  the  blood  are  recognized  by  their  circular  contour  ;  pp.  corresponds  to  an  interlobular 
vein  in  immediate  proximity  with  which  are  the  epithelial  cells  of  the  biliary  ducts,  to  which,  at 
the  lower  part  of  the  figures,  the  much  larger  hepatic  cells  suddenly  succeed.    (E.  Hering.) 

the  peritoneum  with  which  it  is  continuous.  Within  this  is  (2)  the 
fibrous  or  areolar  coat,  constructed  of  tough  fibrous  and  elastic  tissue,  with 
which  is  mingled  a  considerable  number  of  plain  muscular  fibres,  both 
longitudinal  and  circular.  (3)  Internally  the  gall-bladder  is  lined  by 
mucous  membrane,  and  a  layer  of  columnar  epithelium.  The  surface 
of  the  mucous  membrane  presents  to  the  naked  eye  a  minutely  honey- 
combed appearance  from  a  number  of  tiny  polygonal  depressions  with 
intervening  ridges,  by  which  its  surface  is  mapped  out.  In  the  cystic 
duct  the  mucous  membrane  is  raised  up  in  the  form  of  crescentic  folds, 
which  together  appear  like  a  spiral  valve,  and  which  minister  to  the 
function  of  the  gall-bladder  in  retaining  the  bile  during  the  intervals 
of  digestion. 


DIGESTION.  270 

The  gall-bladder  and  all  the  main  biliary  ducts  are  provided  with 
mucous  glands,  which  open  on  their  internal  surface. 

Functions  of  the  Liver. — The  functions  of  the  Liver  may  be 
classified  under  the  following  heads  : — 1.  The  Secretion  of  Bile.  2. 
The  Elaboration  of  Blood  ;  under  this  head  may  be  included  the  Glyco- 
genic Function. 

1.  The  Secretion  of  Bile. 

The  Bile. — Properties. — The  bile  is  a  somewhat  viscid  fluid,  of  a 
yellow  or  a  reddish-yellow  color,  a  strongly  bitter  taste,  and,  when 
fresh,  with  a  scarcely  perceptible  odor:  it  has  a  neutral  or  slightly  alka- 
line reaction,  and  its  specific  gravity  is  about  1020.  Its  color  and  degree 
of  consistence  vary  much,  quite  independent  of  disease;  but,  as  a 
rule,  it  becomes  gradually  more  deeply  colored  and  thicker  as  it  ad- 
vances along  its  ducts,  or  when  it  remains  long  in  the  gall-bladder, 
wherein,  at  the  same  time,  it  becomes  more  viscid  and  ropy,  of  a 
darker  color,  and  more  bitter  taste,  mainly  from  its  greater  degree  of 
concentration,  on  account  of  partial  absorption  of  its  water,  but  partlv 
also  from  being  mixed  with  mucus. 

Chemical  Composition  of  Human  Bile.     (Frerichs.) 


Water, 

..... 

. 

859.2 

Solids- 

-Bile  salts  or  Bilin, 

91.5 

Fat,      ...             . 

.     9.2 

Cholesterin,       .          ... 

2.6 

Mucus  and  coloring  matter*,  . 

.     29.8 

Salts,  .         . 

7.7 

140.8 

1000.0 

(a)  Bile  salts,  or  Bilin,  can  be  obtained  as  colorless,  exceedingly  del- 
iquescent crystals,  soluble  in  water,  alcohol,  and  alkaline  solutions, 
giving  to  the  watery  solution  the  taste  and  general  characters  of  bile. 
They  consist  of  sodium  salts  of  glycocholic  and  taurocholic  acids.  The 
former  salt  is  composed  of  cholic  acid  combined  with  glycin  (see  Ap- 
pendix), the  latter  of  the  same  acid  combined  with  taurin.  The  pro- 
portion of  these  two  salts  in  the  bile  of  different  animals  varies,  e.  g., 
in  ox  bile  the  glycocholate  is  in  great  excess,  whereas  the  bile  of  the  dog. 
cat,  bear,  and  other  carnivora  contains  taurocholate  alone  ;  in  human 
bile  both  are  present  in  about  the  same  amount  (glycocholate  in  excess?). 

Preparation  of  Bile  Salts. — Bile  salts  may  be  prepared  in  the  fol- 
lowing manner:  mix  bile  which  has  been  evaporated  to  a  quarter  of  its 
bulk  with  animal  charcoal,  and  evaporate  to  perfect  dryness  in  a  water 
bath.     Next  extract  the  mass  whilst  still  warm  with   absolute  alcohol. 


280  HANDBOOK    OF    PHYSIOLOGY. 

Separate  the  alcoholic  extract  by  filtration,  and  to  it  add  perfectly  an- 
hydrous ether  as  long  as  a  precipitate  is  thrown  down.  The  solution  and 
precipitate  should  be  set  aside  in  a  closely  stoppered  bottle  for  some  days, 
when  crystals  of  the  bile  salts  or  bilin  will  have  separated  out.  The 
glycocholate  may  be  separated  from  the  taurocholate  by  dissolving  bilin 
in  water,  and  adding  to  it  a  solution  of  neutral  lead  acetate,  and  then  a 
little  basic  lead  acetate,  when  lead  glycocholate  separates  out.  Filter 
and  add  to  the  filtrate  lead  acetate  and  ammonia,  a  precipitate  of  lead 
taurocholate  will  be  formed,  which  may  be  filtered  off.  In  both  cases, 
the  lead  may  be  got  rid  of  by  suspending  or  dissolving  in  hot  alcohol, 
adding  hydrogen  sulphate,  filtering  and  allowing  the  acids  to  separate 
out  by  the  addition  of  water. 

The  Test  for  bile  salts  is  known  as  Pettenkofer's.  If  to  an  aqueous 
solution  of  the  salts  strong  sulphuric  acid  be  added,  the  bile  acids  are 
first  of  all  precipitated,  but  on  the  further  addition  of  the  acid  are  re- 
dissolved.  If  to  the  solution  a  drop  of  solution  of  cane  sugar  be  added, 
a  fine  deep  cherry  red  to  purple  color  is  developed. 

The  reaction  will  also  occur  on  the  addition  of  grape  or  fruit  sugar 
instead  of  cane  sugar,  slowly  with  the  first,  quickly  with  the  last;  and  a 
color  similar  to  the  above  is  produced  by  the  action  of  sulphuric  acid  and 
sugar  on  albumen,  the  crystalline  lens,  nerve  tissue,  oleic  acid,  pure 
ether,  cholesterin,  morphia,  codeia  and  amylic  alcohol. 

The  spectrum  of  Pettenkofer's  reaction,  when  the  fluid  is  moderately 
diluted,  shows  four  bands — the  most  marked  and  largest  at  E,  and  a 
little  to  the  left;  another  at  F;  a  third  between  D  and  E,  nearer  to  D; 
and  a  fourth  near  D. 

(i)  The  yellow  coloring  matter'  of  the  bile  of  man  and  the  Carnivora 
is  termed  Bilirubin  or  Bilifulvin  (C16H]81S"203)  crystallizable  and  insolu- 
ble in  water,  soluble  in  chloroform  or  carbon  disulphide;  a  green  color- 
ing matter,  Biliverdin  (C16H20N"2O.),  which  always  exists  in  large 
amount  in  the  bile  of  Herbivora,  being  formed  from  bilirubin  on  expo- 
sure to  the  air,  or  by  subjecting  the  bile  to  any  other  oxydizing  agency, 
as  by  adding  nitric  acid.  When  the  bile  has  been  long  in  the  gall- 
bladder, a  third  pigment,  Biliprasin,  may  be  also  found  in  small 
amount. 

In  cases  of  biliary  obstruction,  the  coloring  matter  of  the  bile  is  re- 
absorbed, and  circulates  with  the  blood,  giving  to  the  tissues  the  yellow 
tint  characteristic  of  jaundice. 

The  coloring  matters  of  human  bile  do  not  appear  to  give  character- 
istic absorption  spectra;  but  the  bile  of  the  guinea  pig,  rabbit,  mouse, 
sheep,  ox,  and  crow  do  so,  the  most  constant  of  which  appears  to  be  a 
band  at  F.  The  bile  of  the  sheep  and  ox  give  three  bands  in  a  thick 
layer,  and  four  or  five  bands  with  a  thinner  layer,  one  on  each  side  of  D, 
one  near  E,  and  a  faint  line  at  F.     (McMunn.) 


DIGESTION.  s»^l 

There  seems  to  be  a  close  relationship  between  the  color-matters  of 
the  blood  and  of  the  bile,  and  it  may  be  added,  between  these  and  that 
of  the  urine  (urobilin),  and  of  the  faeces  (stercobilin)  also;  it  is  probable 
they  are,  all  of  them,  varieties  of  the  same  pigment,  or  derived  from  the 
same  source.  Indeed  it  is  maintained  that  Urobilin  is  identical  with 
Rydrobilirubin,  a  substance  which  is  obtained  from  bilirubin  by  the 
action  of  sodium  amalgam,  or  by  the  action  of  sodium  amalgam  on  alka. 
line  hsematin;  both  urobilin  and  hydrobilirubin  giving  a  characteristic 
absorption  band  between  b  and  F.  They  are  also  identical  with  sterco- 
bilin, which  is  formed  in  the  alimentary  canal  from  bile  pigments. 

The  Test  (Gmelin's)  for  the  presence  of  bile-pigment  consists  of  the 
addition  of  a  small  quantity  of  nitric  acid,  yellow  with  nitrous  acid;  if 
bile  be  present,  a  play  of  colors  is  produced,  beginning  with  green  and 
passing  through  blue  and  violet  to  red,  and  lastly  to  yellow.     The  spec- 


Fiq.  213. — Crystalline  scales  of  cholesterin. 

trum  of  Gmelin's  test  gives  a  black   band  extending  from  near  b  to 
beyond  F. 

(c)  Fatty  substances  are  found  in  variable  proportions  in  the  bile. 
Besides  the  ordinary  saponifiable  fats,  there  is  a  small  quantity  of  Cho- 
lesterin, a  so-called  non-saponifiable  fat,  which  is  really  an  alcohol,  and, 
with  the  free  fats,  is  probably  held  in  solution  by  the  bile  salts.  It  is  a 
body  belonging  to  the  class  of  monatomic  alcohols  (C26H4<0),  and  crystal- 
lizes in  rhombic  plates  (Fig.  213).  It  is  insoluble  in  water  and  cold 
alcohol,  but  dissolves  easily  in  boiling  alcohol  or  ether.  It  gives  a  red 
color  with  strong  sulphuric  acid,  and  with  nitric  acid  and  ammonia; 
also  a  play  of  colors  beginning  with  blood  red  and  ending  with  green  on 
the  addition  of  sulphuric  acid  and  chloroform.  Lecithin  (C^H^NPOJ, 
a  phosphorus-containing  body  and  Neurin  (C5H]5N02),  are  also  found  in 
bile,  the  latter  probably  as  a  decomposition  product  of  the  former. 

(d)  The  Mucus  in  bile  is  derived  from  the  mucous  membrane  and 
glands  of  the  gall-bladder,  and  of  the  hepatic  ducts.  It  constitutes  the 
residue  after  bile  is  treated  with  alcohol.  The  epithelium  with  which  it 
is  mixed  may  be  detected  in  the  bile  with  the  microscope  in  the  form  of 


282  HANDBOOK    OF   PHYSIOLOGY. 

cylindrical  cells,  either  scattered  or  still  held  together  in  layers.  To  the- 
presence  of  the  mucus  is  probably  to  be  ascribed  the  rapid  decomposition 
of  the  bile;  for,  according  to  Berzelius,  if  the  mucus  be  separated,  it 
"will  remain  unchanged  for  many  days. 

(e)  The  Saline  or  inorganic  constituents  of  the  bile  are  similar  to 
those  found  in  most  other  secreted  fluids.  It  is  possible  that  the  carbo- 
nate and  neutral  phosphate  of  sodium  and  potassium,  found  in  the  ashes 
of  bile,  are  formed  in  the  incineration,  and  do  not  exist  as  such  in  the 
fluid.  Oxide  of  iron  is  said  to  be  a  common  constituent  of  the  ashes  of 
bile,  and  copper  is  generally  found  in  healthy  bile,  and  constantly  in 
biliary  calculi. 

(/)  Gas. — Small  amounts  of  carbonic  acid,  oxygen,  and  nitrogen 
gases  may  be  extracted  from  bile. 

Mode  of  Secretion  and  Discharge. — The  secretion  of  bile  is  continu- 
ally going  on,  but  it  appears  to  be  retarded  during  fasting,  and  accele- 
rated on  taking  food.  This  has  been  shown  by  tying  the  common  bile- 
duct  of  a  dog,  and  establishing  a  fistulous  opening  between  the  skin  and 
gall-bladder,  whereby  all  the  bile  secreted  was  discharged  at  the  surface. 
It  was  noticed  that  when  the  animal  was  fasting,  sometimes  not  a  drop 
of  bile  was  discharged  for  several  hours;  but  that,  in  about  ten  minutes 
after  the  introduction  of  food  into  the  stomach,  the  bile  began  to  flow 
abundantly,  and  continued  to  do  so  during  the  whole  period  of  digestion. 

The  bile  is  formed  in  the  hepatic  cells;  thence,  being  discharged  into 
the  minute  hepatic  ducts,  it  passes  into  the  larger  trunks,  and  from  the 
main  hepatic  duct  may  be  carried  at  once  into  the  duodenum.  But, 
probably,  this  happens  only  while  digestion  is  going  on;  during  fasting, 
it  regurgitates  from  the  common  bile-duct  through  the  cystic  duct,  into 
the  gall-bladder,  where  it  accumulates  till,  in  the  next  period  of  diges- 
tion, it  is  discharged  into  the  intestine.  The  gall-bladder  thus  fulfils 
what  appears  to  be  its  chief  or  only  office,  that  of  a  reservoir;  for  its 
presence  enables  bile  to  be  constantly  secreted,  yet  insures  its  employ- 
ment in  the  service  of  digestion,  although  digestion  is  periodic,  and  the 
secretion  of  bile  constant. 

The  mechanism  by  which  the  bile  passes  into  the  gall-bladder  is 
simple.  The  orifice  through  which  the  common  bile-duct  communicates 
with  the  duodenum  is  narrower  than  the  duct,  and  appears  to  be  closed, 
except  when  there  is  sufficient  pressure  behind  to  force  the  bile  through 
it.  The  pressure  exercised  upon  the  bile  secreted  during  the  intervals 
of  digestion  appears  insufficient  to  overcome  the  force  with  which  the 
orifice  of  the  duct  is  closed;  and  the  bile  in  the  common  duct,  finding 
no  exit  in  the  intestine,  traverses  the  cystic  duct,  and  so  passes  into  the 
gall-bladder,  being  probably  aided  in  this  retrograde  course  by  the  peri- 
staltic action  of  the  ducts.  The  bile  is  discharged  from  the  gall-bladder 
and  enters  the  duodenum  on  the  introduction  of  food  into  the  small  in- 


DIGESTrON.  l's:, 

testine:  being  pressed  on  by  the  contraction  of  the  coats  of  the  gall- 
bladder, and  of  the  common  bile-duct  also;  for  both  these  organs  con- 
tain unstriped  muscular  fibre-cells.  Their  contraction  is  excited  by  the 
stimulus  of  the  food  in  the  duodenum  acting  so  as  to  produce  a  reflex 
movement,  the  force  of  which  is  sufficient  to  open  the  orifice  of  the  com- 
mon bile-duct. 

Bile,  as  such,  is  not  pre-formed  in  the  blood.  As  just  observed,  it  is 
formed  or  secreted  by  the  hepatic  cells,  although  some  of  the  material 
may  be  brought  to  them  almost  in  the  condition  for  immediate  secretion. 
When  it  is,  however,  prevented  by  an  obstruction  of  some  kind,  from 
escaping  into  the  intestine  (as  by  the  passage  of  a  gall-stone  along  the 
hepatic  duct)  it  is  absorbed  in  great  excess  iuto  the  blood,  and,  circulat- 
ing with  it,  gives  rise  to  the  well-known  phenomena  of  jaundice.  This 
is  explained  by  the  fact  that  the  pressure  of  secretion  in  the  ducts  is 
normally  very  low,  and  if  it  exceeds  §  inch  of  mercury  (16  mm.)  the  se- 
cretion ceases  to  be  poured  out,  and  if  the  opposing  force  be  increased, 
the  bile  finds  its  way  into  the  blood. 

Quantity. — Various  estimates  have  been  made  of  the  quantity  of  bile 
discharged  into  the  intestines  in  twenty-four  hours;  the  quantity  doubt- 
less varying,  like  that  of  the  gastric  fluid,  in  proportion  to  the  amount 
of  food  taken.  A  fair  average  of  several  computations  would  give  20  to 
40  oz.  (600-900  cc. )  as  the  quantity  daily  secreted  by  man. 

Functions. — (1)  As  an  excrementitious  substance,  the  bile  may  serve 
especially  as  a  medium  for  the  separation  of  excess  of  carbon  and  hydro- 
gen from  the  blood;  and  its  adaptation  to  this  purpose  is  well  illustrated 
by  the  peculiarities  attending  its  secretion  and  disposal  in  the  foetus. 
During  intra-uterine  life,  the  lungs  and  the  intestinal  canal  are  almost 
inactive  ;  there  is  no  respiration  of  open  air  or  digestion  of  food; 
these  are  unnecessary,  on  account  of  the  supply  of  well  elaborated 
nutriment  received  by  the  vessels  of  the  foetus  at  the  placenta.  The 
liver,  during  the  same  time,  is  proportionately  larger  than  it  is  after 
birth,  and  the  secretion  of  bile  is  active,  although  there  is  no  food  in  the 
intestinal  canal  upon  which  it  can  exercise  any  digestive  property.  At 
birth,  the  intestinal  canal  is  full  of  thick  bile,  mixed  with  intestinal  se- 
cretion; the  meconium,  or  faeces  of  the  foetus,  containing  all  the  essential 
principles  of  bile. 

Composition  of  Meconium  (Frerichs): 

Biliary  resin, 15.6 

Common  fat  and  cholesterin,         ....   15.4 
Epithelium,  mucous,  pigment,  and  salts,  .     69.0 


100.0 
In  the  foetus,  therefore,  the  main  purpose  of  the  secretion  of  bile  must 
be  the  purification  of  blood  by  direct  excretion,  i.e.,  by  separation  from 


.284  HANDBOOK    OF    PHYOLOGY. 

the  blood,  and  ejection  from  the  body  without  further  change.  Probably 
all  the  bile  secreted  in  foetal  life  is  incorporated  in  "the  meconium,  and 
with  it  discharged,  and  thus  the  liver  may  be  said  to  discharge  a  func- 
tion in  some  sense  vicarious  of  that  of  the  lungs.  For,  in  the  foetus, 
nearly  all  the  blood  coming  from  the  placenta  passes  through  the  liver, 
previous  to  its  distribution  to  the  several  organs  of  the  body;  and  the 
abstraction  of  carbon,  hydrogen,  and  other  elements  of  bile  will  purify 
it,  as  in  extra-uterine  life  it  is  purified  by  the  separation  of  carbonic  acid 
and  water  at  the  lungs. 

Disposal  of  the  Bile. — The  evident  disposal  of  the  foetal  bile  by  excre- 
tion, makes  it  highly  probable  that  the  bile  in  extra-uterine  life  is  also, 
at  least  in  part,  destined  to  be  discharged  as  excrementitious.  The 
analysis  of  the  fasces  of  both  children  and  adults  shows,  however,  that 
(except  when  rapidly  discharged  in  purgation)  they  contain  very  little  of 
the  bile  secreted,  probably  not  more  than  one-sixteenth  part  of  its  weight, 
and  that  this  portion  includes  chiefly  its  coloring  matter  in  the  form  of 
stercobilin,  and  some  of  its  fatty  matters,  and  to  only  a  very  slight  de- 
gree, its  salts,  almost  all  of  which  have  been  re-absorbed  from  the  intes- 
tines into  the  blood. 

The  elementary  composition  of  bile-salts  shows  such  a  preponderance 
of  carbon  and  hydrogen,  that  probably,  after  absorption,  it  combines 
with  oxygen,  and  is  excreted  in  the  form  of  carbonic  acid  and  water. 
The  change  after  birth,  from  the  direct  to  the  indirect  mode  of  excre- 
tion of  the  bile  may,  with  much  probability,  be  connected  with  a  purpose 
in  relation  to  the  development  of  heat.  The  temperature  of  the  foetus 
is  maintained  by  that  of  the  parent,  and  needs  no  source  of  heat  within 
itself;  but,  in  extra-uterine  life,  there  is  (as  one  may  say)  a  waste  of 
material  for  heat  when  any  excretion  is  discharged  unoxidized  ;  the  car- 
bon and  hydrogen  of  the  bilin,  therefore,  instead  of  being  ejected  in  the 
f  aeces,  are  re-absorbed,  in  order  that  they  may  be  combined  with  oxygen, 
and  that  in  the  combination  heat  may  be  generated.  It  appears  that 
taurocholic  acid  may  easily  be  split  up  in  the  intestine  into  taurin  and 
cholalic  acid.  The  former  does  not  appear  in  the  fasces,  but  the  latter 
has  been  found  there.  So  that  in  part  it  is  excreted,  but  part  is  re-ab- 
sorbed in  the  intestine  and  returned  to  the  liver.  It  is  probable  that  al- 
though part  of  this  may  unite  to  re-form  glycocholic  or  taurocholic  acid, 
the  remainder  is  united  with  oxygen,  and  is  burnt  off  in  the  form  of  car- 
bonic acid  and  water. 

A  substance,  which  has  been  discovered  in  the  faeces,  and  named  ster- 
corin is  closely  allied  to  cholesterin  ;  and  it  has  been  suggested  that 
while  one  great  function  of  the  liver  is  to  excrete  cholesterin  from  the 
blood,  as  the  kidney  excretes  urea,  the  stercorin  of  faeces  is  the  modified 
form  in  which  cholesterin  finally  leaves  the  body.  Ten  grains  and  a  half 
•  of  stercorin  are  excreted  daily  (A.  Flint). 


DIGESTION.  285- 

From  the  peculiar  manner  in  which  the  liver  is  supplied  wilh  much 
of  the  blood  that  flows  through  it,  it  is  probable  that  this  organ  is  excre- 
tory, not  only  for  such  hydro-carbonaceous  matters  as  may  need  expul- 
sion from  any  portion  of  the  blood,  but  that  it  serves  for  the  direct 
purification  of  the  stream  which,  arriving  by  the  portal  vein,  has  just 
gathered  up  various  substances  in  its  course  through  the  digestive  organs 
— substances  which  may  need  to  be  expelled,  almost  immediately  after 
their  absorption.  For  it  is  easily  conceivable  that  many  things  may  be 
taken  up  during  digestion,  which  not  only  are  unfit  for  purposes  of  nu- 
trition, but  which  would  be  positively  injurious  if  allowed  to  mingle 
with  the  general  mass  of  the  blood.  The  liver,  therefore,  may  be  sup- 
posed placed  in  the  only  road  by  which  such  matters  can  pass  unchanged 
into  the  general  current,  jealously  to  guard  against  .their  further  pro- 
gress, and  turn  them  back  again  into  an  excretory  channel.  The  fre- 
quency with  which  metallic  poisons  are  either  excreted  by  the  liver,  or 
intercepted  and  retained,  often  for  a  considerable  time,  in  its  own  sub- 
stance, may  be  adduced  as  evidence  for  the  probable  truth  of  this  sup- 
position. 

(2.)  As  a  digestive  fluid. — Though  one  chief  purpose  of  the  secretion 
of  bile  may  thus  appear  to  be  the  purification  of  the  blood  by  ultimate  ex- 
cretion, yet  there  are  many  reasons  for  believing  that,  while  it  is  in  the 
intestines,  it  performs  an  important  part  in  the  process  of  digestion.  In 
nearly  all  animals,  for  example,  the  bile  is  discharged,  not  through  an 
excretory  duct  communicating  with  the  external  surface  or  with  a 
simple  reservoir,  as  most  excretions  are,  but  is  made  to  pass  into  the  in- 
testinal canal,  so  as  to  be  mingled  with  the  chyme  directly  after  it  leaves 
the  stomach  ;  an  arrangement,  the  constancy  of  which  clearly  indicates 
that  the  bile  has  some  important  relations  to  the  food  with  which  it  is 
thus  mixed.  A  similar  indication  is  furnished  also  by  the  fact  that  the 
secretion  of  bile  is  most  active,  and  the  quantity  discharged  into  the  in- 
testines much  greater,  during  digestion  than  at  any  other  time  ;  al- 
though, without  doubt,  this  activity  of  secretion  during  digestion  may, 
however,  be  in  part  ascribed  to  the  fact  that  a  greater  quantity  of  blood 
is  sent  through  the  portal  vein  to  the  liver  at  this  time,  and  that  this 
blood  contains  some  of  the  materials  of  the  food  absorbed  from  the 
stomach  and  intestines,  which  may  need  to  be  excreted,  either  tempora- 
rily (to  be  afterwards  re-absorbed),  or  permanently. 

Eespecting  the  functions  discharged  by  the  bile  in  digestion,  there  is 
little  doubt  that  it  (a.)  assists  in  emulsifying  the  fatt y  portions  of  the 
food,  and  thus  rendering  them  capable  of  being  absorbed  by  the  lacteals. 
For  it  has  appeared  in  some  experiments  in  which  the  common  bile-duct 
was  tied,  that,  although  the  process  of  digestion  in  the  stomach  was  un- 
affected, chyle  was  no  longer  well    formed  :  the  contents  of  the  lacteals 


236  HANDBOOK    OF   PHYSIOLOGY. 

consisting  of  clear,  colorless  fluid,  instead  of  being  opaque  and  white,  as 
they  ordinarily  are,  after  feeding. 

(b  )  It  is  probable,  also,  that  the  moistening  of  the  mucous  membrane 
of  the  intestines  by  bile  facilitates  absorption  of  fatty  matters  through  it. 

(c.)  The  bile,  like  the  gastric  fluid,  has  a  considerable  antiseptic 
power,  and  may  serve  to  prevent  the  decomposition  of  food  during  the 
time  of  its  sojourn  in  the  intestines.  Experiments  show  that  the  con- 
tents of  the  intestines  are  much  more  fcetid  after  the  common  bile-duct 
has  been  tied  than  at  other  times  :  moreover,  it  is  found  that  the  mix- 
ture of  bile  with  a  fermenting  fluid  stops  or  spoils  the  process  of  fermen- 
tation. 

(d.)  The  bile  has  also  been  considered  to  act  as  a  natural  purgative, 
by  promoting  an  increased  secretion  of  the  intestinal  glands,  and  by 
stimulating  the  intestines  to  the  propulsion  of  their  contents.  This 
yiew  receives  support  from  the  constipation  which  ordinarily  exists  in 
jaundice,  from  the  diarrhoea  which  accompanies  excessive  secretion  of 
bile,  and  from  the  purgative  properties  of  ox-gall. 

(e.)  The  bile  appears  to  have  the  power  of  precipitating  the  gastric 
parapeptones  and  peptones,  together  with  the  pepsin,  which  is  mixed  up 
with  them,  as  soon  as  the  contents  of  the  stomach  meet  it  in  the  duode- 
num. The  purpose  of  this  operation  is  probably  both  to  delay  any 
change  in  the  parapeptones  until  the  pancreatic  juice  can  act  upon  them, 
and  also  to  prevent  the  pepsin  from  exercising  its  solvent  action  on  the 
ferments  of  the  pancreatic  juice. 

II.  Blood-elabokation. 

The  secretion  of  bile,  as  already  observed,  is  only  one  of  the  purposes 
fulfilled  by  the  liver.  Another  very  important  function  appears  to  be 
that  of  so  acting  upon  certain  constituents  of  the  blood  passing  through 
it,  as  to  render  some  of  them  capable  of  assimilation  with  the  blood 
generally,  and  to  prepare  others  for  being  duly  eliminated  in  the  process 
of  respiration.  It  appears  that  the  peptones,  conveyed  from  the  alimen- 
tary canal  by  the  blood  of  the  portal  vein,  require  to  be  submitted  to 
the  influence  of  the  liver  before  they  can  be  assimilated  by  the  blood; 
for  if  such  albuminous  matter  is  injected  into  the  jugular  vein,  it 
speedily  appears  in  the  urine  ;  but  if  introduced  into  the  portal  vein, 
and  thus  allowed  to  traverse  the  liver,  it  is  no  longer  ejected  as  a  foreign 
substance,  but  is  incorporated  with  the  albuminous  part  of  the  blood. 

Glycogenic  Function. 

One  of  the  chief  uses  of  the  liver  in  connection  with  that  elaboration 
of  the  blood  is  known  as  its  glycogenic  function.  The  important  fact 
that  the  liver  normally  forms  glucose,  or  a  substance  readily  convertible 


DIGESTION.  287 

into  it,  was  discovered  by  Claude  Bernard  in  the  following  way:  he  fed 
a  dog  for  seven  days  with  food  containing  a  large  quantity  of  sugar  and 
starch;  and,  as  might  be  expected,  found  sugar  in  both  the  portal  and 
hepatic  veins.  And  this  dog  was  fed  with  meat  only,  and,  to  his  sur- 
prise, sugar  was  still  found  in  the  hepatic  veins.  Eepeated  experiments 
gave  invariably  the  same  result;  no  sugar  being  found,  under  a  meat 
diet,  in  the  portal  vein,  if  care  were  taken,  by  applying  a  ligature  on  it 
at  the  transverse  fissure,  to  prevent  reflux  of  blood  from  the  hepatic  ve- 
nous system.  Bernard  found  sugar  also  in  the  substance  of  the  liver. 
It  thus  seemed  certain  that  the  liver  formed  sugar,  even  when,  from  the 
absence  of  saccharine  and  amyloid  matters  in  the  food,  none  could  be 
brought  directly  to  it  from  the  stomach  or  intestines. 

Excepting  cases  in  which  large  quantities  of  starch  and  sugar  were 
taken  as  food,  no  sugar  was  found  in  the  blood  after  it  had  passed  through 
the  lungs;  the  sugar  formed  by  the  liver,  having  presumably  disappeared 
by  combustion,  in  the  course  of  the  pulmonary  circulation. 

Bernard  found,  subsequently  to  the  before-mentioned  experiments, 
that  a  liver,  removed  from  the  body,  and  from  which  all  sugar  had  been 
completely  washed  away  by  injecting  a  stream  of  water  through  its  blood- 
vessels, will  be  found,  after  the  lapse  of  a  few  hours,  to  contain  sugar  in 
abundance.  This  post-mortem  production  of  sugar  was  a  fact  which 
could  only  be  explained  in  the  supposition  that  the  liver  contained  a 
substance,  readily  convertible  into  sugar  in  the  course  merely  of  post- 
mortem decomposition;  and  this  theory  was  proved  correct  by  the  dis- 
covery of  a  substance  in  the  liver  allied  to  starch,  and  now  generally 
termed  glycogen.  We  may  believe,  therefore,  that  the  liver  does  not 
form  sugar  directly  from  the  materials  brought  to  it  by  the  blood,  but 
that  glycogen  is  first  formed  and  stored  in  its  substance,  and  that  the 
sugar,  when  present,  is  the  result  of  the  transformation  of  the  latter. 

Quantity  of  Glycogen  formed. — Although,  as  before  mentioned,  gly- 
cogen is  produced  by  the  liver  when  neither  starch  nor  sugar  is  present 
in  the  food,  its  amount  is  much  less  under  such  a  diet. 

Average  amount  of  Glycogen  in  the  Liver  of  Dogs  under  various  Diets 

(Pavy). 

Diet.  Amount  of  Glycogen  in  Liver. 

Animal  food, 7.19  per  cent. 

Animal  food  with  sugar  (about  |-  lb.  of  sugar  daily),     .     14.5         " 
Vegetable  diet  (potatoes,  with  bread  or  barley-meal),    .     17.23 

The  dependence  of  the  formation  of  glycogen  on  the  food  taken  is 
also  well  shown  by  the  following  results,  obtained  by  the  same  experi- 
menter:— 


288  HANDBOOK    OF   PHYSIOLOGY. 

Average  quantity  of  Glycogen  found  in  the  Liver  of  Rabbits  after  Fast- 
ing, and  after  a  diet  of  Starch  and  Sugar  respectively. 

Average  Amount  of  Glycogen  in  Liver. 
After  fasting  for  three  days,  .         .         .         Practically  absent. 
"     diet  of  starch  and  grape-sugar.         .     15.4  per  cent. 
"  "      cane-sugar,         .         .         .         16.9       " 

Eegarding  these  facts  there  is  no  dispute.  All  are  agreed  that  gly- 
cogen is  formed,  and  laid  up  in  store,  temporarily,  by  the  livei -cells;  and 
that  it  is  not  formed  exclusively  from  saccharine  and  amylaceous  foods, 
but  from  albuminous  substances  also;  the  albumen,  in  the  latter  case, 
being  probably  split  up  into  glycogen,  which  is  temporarily  stored  in  the 
liver,  and  urea,  which  is  excreted  by  the  kidneys. 

Destination  of  Glycogen. — There  are  two  chief  theories  on  the  subject 
of  the  destination  of  glycogen.  (1.)  That  the  conversion  of  glycogen 
into  sugar  takes  place  rapidly  during  life  by  the  agency  of  a  ferment 
{liver  diastase)  also  formed  in  the  liver:  and  the  sugar  is  conveyed  away 
by  the  blood  of  the  hepatic  veins,  and  soon  undergoes  combustion.  (2  ) 
That  the  conversion  into  sugar  only  occurs  after  death,  and  that  during 
life  no  sugar  exists  in  healthy  livers;  glycogen  not  undergoing  this  trans- 
formation. The  chief  arguments  advanced  in  support  of  this  view  are, 
(a)  that  scarcely  a  trace  of  sugar  is  found  in  blood  drawn  during  life 
from  the  right  ventricle,  or  in  blood  collected  from  the  right  side  of  the 
heart  immediately  niter  an  animal  has  been  killed;  while  if  the  examina- 
tion be  delayed  for  a  very  short  time  after  death,  sugar  in  abundance 
may  be  found  in  such  blood;  (b),  that  the  liver,  like  the  venous  blood  in 
the  heart,  is,  at  the  moment  of  death,  completely  free  from  sugar,  al- 
though afterwards  its  tissue  speedily  becomes  saccharine,  unless  the 
formation  of  sugar  be  prevented  by  freezing,  boiling,  or  other  means 
calculated  to  interfere  with  the  action  of  a  ferment  on  the  amyloid  sub- 
stance of  the  organ.  Instead  of  adopting  Bernard's  view,  that  normally, 
during  life,  glycogen  passes  as  sugar  into  the  hepatic  venous  blood,  and 
thereby  is  conveyed  to  the  lungs  to  be  further  disposed  of,  Pavy  inclines 
to  the  belief  that  it  may  represent  an  intermediate  stage  in  the  formation 
of  fat  from  materials  absorbed  from  the  alimentary  canal. 

Liver-Sugar. — To  demonstrate  the  presence  of  sugar  in  the  liver,  a 
portion  of  this  organ,  after  being  cut  into  small  pieces,  is  bruised  in  a 
mortar  to  a  pulp  with  a  small  quantity  of  water,  and  the  pulp  is  boiled 
with  sodium-sulphate  in  order  to  precipitate  albuminous  and  coloring 
matters.     The  decoction  is  then  filtered  and  may  be  tested  for  glucose. 

Glqcoqen  (Ce  H1U  06)  is  an  amorphous,  starch-like  substance,  odorless 
and  tasteless,  soluble  in  water,  insoluble  in  alcohol.  It  is  converted  into 
glucose  by  boiling  with  dilute  acids,  or  by  contact  with  any  animal  fer- 
ment. It  may  be  obtained  by  taking  a  portion  of  liver  from  a  recently 
killed  rabbit,  and  after  cutting  it  into  small  pieces,  placing  it  for  a  short 
time  in  boiling  water.     It  is  then  bruised  in  a  mortar,  until  it  forms  a 


DIGESTION.  280 

pulpy  mass,  and  subsequently  boiled  in  distilled  water  for  about  a  quarter 
of  an  hour.  The  glycogen  is  precipitated  from  the  filtered  decoction  by 
the  addition  of  alcohol.  Glycogen  has  been  found  in  many  other  struc- 
tures than  the  liver  (See  Appendix). 

Glycosuria. — The  facility  with  which  the  glycogen  of  the  liver  is 
transformed  into  sugar  would  lead  to  the  expectation  that  this  chemical 
change,  under  many  circumstances,  would  occur  to  such  an  extent  that 
sugar  would  be  present  not  only  in  the  hepatic  veins,  but  in  the  blood 
generally.  Such  is  frequently  the  case;  the  sugar  when  in  excess  in  the 
blood  being  secreted  by  the  kidneys,  and  thus  appearing  in  variable 
quantities  in  the  urine  (Glycosuria). 

Influence  of  the  Nervous  System. — Glycosuria  maybe  experimentally 
produced  by  puncture  of  the  medulla  oblongata  in  the  region  of  the 
vaso-motor  centre.  The  better  fed  the  animal  the  larger  is  the  amount 
of  sugar  found  in  the  urine;  whereas  in  the  case  of  a  starving  animal  no 
sugar  appears.  It  is,  therefore,  highly  probable  that  the  sugar  comes 
from  the  hepatic  glycogen,  since  in  the  one  case  glycogen  is  in  excess, 
and  in  the  other  it  is  almost  absent.  The  nature  of  the  influence  is 
uncertain.  It  may  be  exercised  in  dilating  the  hepatic  vessels,  or  pos- 
sibly may  be  exerted  on  the  liver  cells  themselves.  The  whole  course 
of  the  nervous  stimulus  cannot  be  traced  to  the  liver,  but  at  first  it 
passes  from  the  lower  part  of  the  floor  of  the  fourth  ventricle  and 
medulla  down  the  spinal  cord  as  far  as — in  rabbits— the  fourth  dorsal 
vertebra,  and  thence  to  the  first  thoracic  ganglion. 

Many  other  circumstances  will  cause  glycosuria.  It  has  been  ob- 
served after  the  administration  of  various  drugs,  after  the  injection  of 
urari,  poisoning  with  carbonic  oxide  gas,  the  inhalation  of  ether,  chloro- 
form, etc.,  the  injection  of  oxygenated  blood  into  the  portal  venous  sys- 
tem. It  has  been  observed  in  man  after  injuries  to  the  head,  and  in  the 
course  of  various  diseases. 

The  well-known  disease,  diabetes  mellitus,  in  which  a  large  quantity 
of  sugar  is  persistently  secreted  daily  with  the  urine,  has,  doubtless, 
some  close  relation  to  the  normal  glycogenic  function  of  the  liver;  but 
the  nature  of  the  relationship  is  at  present  quite  unknown. 

The  Intestinal  Secketion,  or  Succus  Entericus. 

On  account  of  the  difficulty  in  isolating  the  secretion  of  the  glands 
in  the  wall  of  the  intestine  (Brunner's  and  Lieberkuhn's)  from  other 
secretions  poured  into  the  canal  (gastric  juice,  bile,  and  pancreatic  secre- 
tion), but  little  is  known  regarding  the  composition  of  the  former  fluid 
(intestinal  juice,  succus  entericus). 

It  is  said  to  be  a  yellowish  alkaline  fluid  with  a  specific  gravity  of 
1011,  and  to  contain  about  2.5  per  cent  of  solid  matters  (Thiry). 
19 


290  HANDBOOK    OF    PHYSIOLOGY. 

Functions. — The  secretion  of  Brunner's  glands  is  said  to  be  able  to 
convert  proteids  into  peptones,  and  that  of  Lieberkiihn's  is  believed  to 
convert  starch  into  sugar.  To  these  functions  of  the  succus  entericus 
the  powers  of  converting  cane  into  grape  sugar,  and  of  turning  grape 
sugar  into  lactic,  and  afterwards  into  butyric  acid,  are  added  by  some 
physiologists.  It  also  probably  contains  a  milk-curdling  ferment  (W. 
Roberts). 

The  reaction  which  represents  the  conversion  of  cane  sugar  into 
grape  sugar  may  be  represented  thus: — 

2C„HM0H      +■     2H20      =      C12H24012      +      C12H24012 
Saccharose  Water  Dextrose  Lsevulose 

The  conversion  is  effected  probably  by  means  of  a  hydrolytic  fer- 
ment.    (Inversive  ferment,  Bernard.) 

The  length  and  complexity  of  the  digestive  tract  seem  to  be  closely 
connected  with  the  character  of  the  food  on  which  an  animal  lives. 
Thus  in  all  carnivorous  animals,  such  as  the  cat  and  dog,  and  pre-emi- 
nently in  carnivorous  birds,  as  hawksand  herons,  it  is  exceedingly  short. 
The  seals,  which,  though  carnivorous,  possess  a  very  long  intestine, 
appear  to  furnish  an  exception;  but  this  is  doubtless  to  be  explained  as 
an  adaptation  to  their  aquatic  habits,  their  constant  exposure  to  cold  re- 
quiring that  they  should  absorb  as  much  as  possible  from  their  intestines. 

Herbivorous  animals,  on  the  other  hand,  and  the  ruminants  espe- 
cially, have  very  long  intestines  (in  the  sheep  30  times  the  length  of  the 
body),  which  is  no  doubt  to  be  connected  with  their  lowly  nutritious 
diet.  In  others,  such  as  the  rabbit,  though  the  intestines  are  not  ex- 
cessively long,  this  is  compensated  by  the  great  length  and  capacity  of 
the  caecum.  In  man,  the  length  of  the  intestines  is  intermediate  be- 
tween the  extremes  of  the  carnivora  and  herbivora,  and  his  diet  also  is 
intermediate. 

Summary  of  the  Digestive  Changes  in  the  Small  Intestine. 

In  order  to  understand  the  changes  in  the  food  which  occur  during 
its  passage  through  the  small  intestine,  it  will  be  well  to  refer  briefly  to 
the  state  in  which  it  leaves  the  stomach  through  the  pylorus.  It  has 
been  said  before,  that  the  chief  office  of  the  stomach  is  not  only  to  mix 
into  an  uniform  mass  all  the  varieties  of  food  that  reach  it  through  the 
oesophagus,  but  especially  to  dissolve  the  nitrogenous  portion  by  means 
of  the  gastric  juice.  The  fatty  matters,  during  their  sojourn  in  the 
stomach,  become  more  thoroughly  mingled  with  the  other  constituents 
of  the  food  taken,  but  are  not  yet  in  a  state  fit  for  absorption.  The 
conversion  of  starch  into  sugar,  which  began  in  the  mouth,  has  been  in- 
terfered with,  if  not  altogether  stopped.  The  soluble  matters — both 
those  which  were  so  from  the  first,  as  sugar  and  saline  matter,  and  the 
gastric  peptones — have  begun  to  disappear  by  absorption  into  the  blood- 
vessels, and  the  same  thing  has  befallen  such  fluids  as  may  have  been 
swallowed — wine,  water,  etc. 


DIGESTION.  291 

The  thin  pultaceous  chyme,  therefore,  which,  during  the  whole  period 
of  gastric  digestion,  is  being  constantly  squeezed  or  strained  through 
the  pyloric  orifice  into  the  duodenum,  consists  of  albuminous  matter, 
broken  down,  dissolving  and  half  dissolved;  fatty  matter  broken  down 
and  melted,  but  not  dissolved  at  all;  starch  very  slowly  in  process  of 
conversion  into  sugar,  and  as  it  becomes  sugar,  also  dissolving  in  the 
fluids  with  which  it  is  mixed;  while,  with  these  are  mingled  gastric  fluid, 
and  fluid  that  has  been  swallowed,  together  with  such  portions  of  the 
food  as  are  not  digestible,  and  will  be  finally  expelled  as  part  of  the 
faeces. 

On  the  entrance  of  the  chyme  into  the  duodenum,  it  is  subjected 
to  the  influence  of  the  bile  and  pancreatic  juice,  which  are  then  poured 
out,  and  also  to  that  of  the  succus  entericus.  All  these  secretions  have 
a  more  or  less  alkaline  reaction,  and  by  their  admixture  with  the  gastric 
chyme,  its  acidity  become  less  and  less  until  at  length,  at  about  the 
middle  of  the  small  intestine,  the  reaction  becomes  alkaline  and  con- 
tinues so  as  far  as  the  ileo-caecal  valve. 

The  special  digestive  functions  of  the  small  intestine  may  be  taken  in 
the  following  order: — 

(1.)  One  important  duty  of  the  small  intestine  is  the  alteration  of 
the  fat  in  such  a  manner  as  to  make  it  fit  for  absorption;  and  there  is  no 
doubt  that  this  change  is  chiefly  effected  in  the  upper  part  of  the  small 
intestine.  What  is  the  exact  share  of  the  process,  however,  allotted  re- 
spectively to  the  bile,  to  the  pancreatic  secretion,  and  to  the  intestinal 
juice,  is  still  uncertain.  The  fat  is  changed  in  two  ways,  (a.)  To  a 
slight  extent  it  is  chemically  decomposed  by  the  alkaline  secretions  with 
which  it  is  mingled,  and  a  soap  is  the  result,  (b.)  It  is  emulsionized, 
i.  e.,  its  particles  are  minutely  subdivided  and  diffused,  so  that  the  mix- 
ture assumes  the  condition  of  a  milky  fluid  or  emulsion.  As  will  be  seen 
in  the  next  Chapter,  most  of  the  fat  is  absorbed  by  the  lacteals  of  the 
intestine,  but  a  small  part,  which  is  saponified,  is  also  absorbed  by  the 
blood-vessels. 

(2.)  The  albuminous  substances  which  have  been  partly  dissolved  in 
the  stomach,  and  have  not  been  absorbed,  are  subjected  to  the  action  of 
the  pancreatic  and  intestinal  secretions.  The  pepsin  is  rendered  inert 
by  being  precipitated  together  with  the  gastric  peptones  and  parapep- 
tones,  as  soon  as  the  chyme  meets  with  bile.  By  these  means  the  pan- 
creatic ferment  trypsin  is  enabled  to  proceed  with  the  further  conversion 
of  the  parapeptones  into  peptones,  and  of  part  of  the  peptones  (hemipep- 
tone,  Kuhne)  intoleucin  and  tyrosin.  Albuminous  substances,  which  are 
chemically  altered  in  the  process  of  digestion  (peptones)  and  gelatinous 
matters  similarly  changed,  are  absorbed  by  the  blood-vessels  and  lym- 
phatics of  the  intestinal  mucous  membrane.  Albuminous  matters,  in 
state  of  solution,  which  have   not   undergone  the  peptonic  change,  are 


292  HANDBOOK    OF    PHYSIOLOGY. 

probably,  from  tbe  difficulty  with  which  they  diffuse,  absorbed,  if  at  all, 
almost  solely  by  the  lymphatics. 

(3.)  The  starchy,  or  amyloid  portions  of  the  food,  the  conversion  of 
which  into  dextrin  and  sugar  was  more  or  less  interrupted  during  iti 
stay  in  the  stomach,  is  now  acted  on  briskly  by  the  pancreatic  juice  and 
the  succus  entericus;  and  the  sugar  as  it  is  formed,  is  dissolved  in  the 
intestinal  fluids,  and  is  absorbed  chiefly  by  the  blood-vessels. 

(4.)  Saline  and  saccharine  matters,  as  common  salt,  or  cane  sugar, 
if  not  in  a  state  of  solution  beforehand  in  the  saliva  or  other  fluids  which 
may  have  been  swallowed  with  them,  are  at  once  dissolved  in  the 
stomach,  and  if  not  here  absorbed,  are  soon  taken  up  in  the  small  intes- 
tine; the  blood-vessels,  as  in  the  last  case,  being  chiefly  concerned  in  the 
absorption.  Cane  sugar  is  in  part  or  wholly  converted  into  grape-sugar 
before  its  absorption.  This  is  accomplished  partially  in  the  stomach, 
but  also  by  a  ferment  in  the  succus  entericus. 

(5.)  The  liquids,  including  in  this  term  the  ordinary  drinks,  as  water, 
wine,  ale,  tea,  etc.,  which  may  have  escaped  absorption  in  the  stomach, 
are  absorbed  probably  very  soon  after  their  entrance  into  the  intestine; 
the  fluidity  of  the  contents  of  the  latter  being  preserved  more  by  the 
constant  secretion  of  fluid  by  the  intestinal  glands,  pancreas,  and  liver, 
than  by  any  given  portion  of  fluid,  whether  swallowed  or  secreted,  re- 
maining long  unabsorbed.  From  this  fact,  therefore,  it  may  be  gathered 
that  there  is  a  kind  of  circulation  constantly  proceeding  from  the  intes- 
tines into  the  blood,  and  from  the  blood  into  the  intestines  again;  for  as 
all  the  fluid — a  very  large  amount — secreted  by  the  intestinal  glands, 
must  come  from  the  blood,  the  latter  would  be  too  much  drained,  were 
it  not  that  the  same  fluid  after  secretion  is  again  re-absorbed  into  the 
current  of  blood — going  into  the  blood  charged  with  nutrient  products 
of  digestion — coming  out  again  by  secretion  through  the  glands  in  a 
comparatively  uncharged  condition. 

At  the  lower  end  of  the  small  intestine,  the  chyme,  still  thin  and 
pultaceous,  is  of  a  light  yellow  color,  and  has  a  distinctly  faecal  odor. 
This  odor  depends  upon  the  formation  of  indol  and  its  allies.  In 
this  state  it  passes  through  the  ileo-caecal  opening  into  the  large  in- 
testine. 

Summary  of  the  Digestive    Changes  in    the  Large 
Intestine. 

The  changes  which  take  place  in  the  chyme  in  the  large  intestine  are 
probably  only  the  continuation  of  the  same  changes  that  occur  in  the 
course  of  the  food's  passage  through  the  upper  part  of  the  intestinal  canal. 
From  the  absence  of  villi,  however,  we  may  conclude  that  absorption, 
especially  of  fatty  matter,  is  in  great  part  completed  in  the  small  intes- 
tine; while,  from  the  still  half-liquid,    pultaceous   consistence  of  the 


DIGESTION.  293 

chyme  when  it  first  enters  the  caecum,  there  can  be  no  doubt  that  the 
absorption  of  liquid  is  not  by  any  means  concluded.  The  peculiar  odor, 
moreover,  which  is  acquired  after  a  short  time  by  the  contents  of  the 
large  bowel,  would  seem  to  indicate  a  further  chemical  change  in  the 
alimentary  matters  or  in  the  digestive  fluids,  or  both.  The  acid  reac- 
tion, which  had  disappeared  in  the  small  bowel,  again  becomes  very 
manifest  in  the  caecum — probably  from  acid  fermentation-processes  in 
some  of  the  materials  of  the  food. 

There  seems  no  reason  to  conclude  that  any  special  'secondary  diges- 
tive '  process  occurs  in  the  caecum  or  in  any  other  part  of  the  large  in- 
testine. Probably  any  constituent  of  the  food  which  has  escaped  diges- 
tion and  absorption  in  the  small  bowel  may  be  digested  in  the  large 
intestine;  and  the  power  of  this  part  of  the  intestinal  canal  to  digest 
fatty,  albuminous,  or  other  matters,  may  be  gathered  from  the  good 
effects  of  nutrient  enemata,  so  frequently  given  when  from  any  cause 
there  is  difficulty  in  introducing  food  into  the  stomach.  In  ordinary 
healthy  digestion,  however,  the  changes  which  ensue  in  the  chyme  after 
its  passage  into  the  large  intestine,  are  mainly  the  absorption  of  the 
more  liquid  parts;  the  chief  function  of  the  large  intestine  being  to  act 
:as  a  reservoir  for  the  residues  of  digestion  before  their  expulsion  from  the 
body. 

Movements  of  the  Intestines. 

It  remains  only  to  consider  the  manner  in  which  the  food  and  the 
several  secretions  mingled  with  it  are  moved  through  the  intestinal  canal, 
so  as  to  be  slowly  subjected  to  the  influence  of  fresh  portions  of  intes- 
tinal secretion,  and  as  slowly  exposed  to  the  absorbent  power  of  all  the 
villi  and  blood-vessels  of  the  mucous  membrane.  The  movement  of  the 
intestines  is  peristaltic  or  vermicular,  and  is  effected  by  the  alternate 
contractions  and  dilatations  of  successive  portions  of  the  intestinal  coats. 
The  contractions,  which  may  commence  at  any  point  of  the  intestine, 
extend  in  a  wave-like  manner  along  the  tube.  In  any  given  portion,  the 
longitudinal  muscular  fibres  contract  first,  or  more  than  the  circular  ; 
they  draw  a  portion  of  the  intestine  upwards,  or,  as  it  were,  backwards, 
over  the  substance  to  be  propelled,  and  then  the  circular  fibres  of  the 
same  portion  contracting  in  succession  from  above  downwards,  or,  as  it 
were,  from  behind  forwards,  press  on  the  substance  into  the  portion  next 
below,  in  which  at  once  the  same  succession  of  action  next  ensues.  These 
movements  take  place  slowly,  and,  in  health,  commonly  give  rise  to  no 
sensation;  but  they  are  perceptible  when  they  are  accelerated  under  the 
influence  of  any  irritant. 

The  movements  of  the  intestines  are  sometimes  retrograde;  and  there 
is  no  hindrance  to  the  backward  movement  of  the  contents  of  the  small 
intestine.     But  almost  complete  security  is  afforded  against  the  passage 


294  HANDBOOK   OF   PHYSIOLOGY. 

of  the  contents  of  the  large  into  the  small  intestine  by  the  ileo-cascal 
valve.  Besides,  the  orifice  of  communication  between  the  ileum  and 
caecum  (at  the  borders  of  which  orifice  are  the  folds  of  mucous  mem- 
brane which  form  the  valve)  is  encircled  with  muscular  fibres,  the  con- 
traction of  which  prevents  the  undue  dilatation  of  the  orifice. 

Proceeding  from  above  downwards,  the  muscular  fibres  of  the  large 
intestine  become,  on  the  whole,  stronger  in  direct  proportion  to  the 
greater  strength  required  for  the  onward  moving  of  the  faeces,  which  are 
gradually  becoming  firmer.  The  greatest  strength  is  in  the  rectum,  at 
the  termination  of  which  the  circular  unstriped  muscular  fibres  form  a 
strong  band  called  the  internal  sphincter ;  while  an  external  sphincter 
muscle  with  striped  fibres  is  placed  rather  lower  down,  and  more  exter- 
nally, and  as  we  have  seen  above,  holds  the  orifice  close  by  a  constant 
slight  tonic  contraction. 

Experimental  irritation  of  the  brain  or  cord  produces  no  evident  or 
constant  effect  on  the  movements  of  the  intestines  during  life  ;  yet  in 
consequence  of  certain  mental  conditions  the  movements  are  accelerated 
or  retarded  ;  and  in  paraplegia  the  intestines  appear  after  a  time  much 
weakened  in  their  power,  and  costiveness,  with  a  tympanitic  condition, 
ensues.  Immediately  after  death,  irritation  of  both  the  sympathetic  and 
pneumogastric  nerves,  if  not  too  strong,  induces  genuine  peristaltic 
movements  of  the  intestines.  Violent  irritation  stops  the  movements. 
These  stimuli  act,  no  doubt,  not  directly  on  the  muscular  tissue  of  the 
intestine,  but  on  the  ganglionic  plexus  before  referred  to. 

Influence  of  the  Nervous  System  on  Intestinal  Digestion. 

As  in  the  case  of  the  oesophagus  and  stomach,  the  peristaltic  move- 
ments of  the  intestines  are  directly  due  to  reflex  action  through  the  gang- 
lia and  nerve  fibres  distributed  so  abundantly  in  their  walls  (p.  25S)  ; 
the  presence  of  chyme  acting  as  the  stimulus,  and  few  or  no  movements 
occurring  when  the  intestines  are  empty.  The  intestines  are,  moreover, 
connected  with  the  higher  nerve-centres  by  the  splanchnic  nervesj  as 
well  as  other  branches  of  the  sympathetic  which  come  to  them  from  the. 
coeliac  and  other  abdominal  plexuses. 

The  splanchnic  nerves  are  in  relation  to  the  intestinal  movements,. 
inhibitory — these  movements  being  retarded  or  stopped  when  the 
splanchnics  are  irritated.  As  the  vaso-motor  nerves  of  the  intestines,, 
the  splanchnics  are  also  much  concerned  in  intestinal  digestion. 

Duration  of  Intestinal  Digestive  Period. — The  time  occupied  by 
the  journey  of  a  given  portion  of  food  from  the  stomach  to  the  anus, 
varies  considerably  even  in  health,  and  on  this  account  probably  it  is. 
that  such  different  opinions  have  been  expresed  in  regard  to  the  subject. 
About  twelve  hours  are  occupied  by  the  journey  of  an  ordinary  meal 


DIGESTION. 


295 


through  the  small  intestine,  and  twenty-four  to  thirty-six  hours  by  the 
passage  through  the  large  bowel. 

The  contents  of  the  large  intestine,  as  they  proceed  towards  the  rec- 
tum, become  more  and  more  solid,  and  losing  their  more  liquid  and  nu- 
trient parts,  gradually  acquire  the  odor  and  consistence  characteristic  of 
faces.  After  a  sojourn  of  uncertain  duration  in  the  sigmoid  flexure  of 
the  colon,  or  in  the  rectum,  they  are  finally  expelled  by  the  act  of  defal- 
cation. 

The  average  quantity  of  solid  fsecal  matter  evacuated  by  the  human 
adult  in  twenty-four  hours  is  about  six  or  eight  ounces. 


Composition  of  Faeces. 


Water,    . 
Solids  : 


Special  excrementitious  constituents  : — Excretin,  ex- 
cretoleic  acid  (Marcet),  and  stercorin  (Austin 
Flint). 

Salts :— Chiefly  phosphate  of  magnesium  and  phos- 
phate of  calcium,  with  small  quantities  of  iron, 
soda,  lime,  and  silica. 

Insoluble  residue  of  the  food  (chiefly  starch  grains, 
woody  tissue,  particles  of  cartilage  and  fibrous 
tissue,  undigested  muscular  fibres  or  fat,  and  the 
like,  with  insoluble  substances  accidentally  in- 
troduced with  the  food. 

Mucus,  epithelium,  altered  coloring  matter  of  bile, 
fatty  acids,  etc. 

Varying  quantities  of  other  constituents  of  bile,  and 
derivatives  from  them. 


.  733.00 


267.00 


1000 


Defalcation. — The  act  of  the  expulsion  of  fseces  is  in  part  due  to  an 
increased  reflex  peristaltic  action  of  the  lower  part  of  the  large  intes- 
tine, namely  of  the  sigmoid  flexure  and  rectum,  and  in  part  to  the  more 
or  less  voluntary  action  of  the  abdominal  muscles.  In  the  case  of  active 
voluntarjr  efforts,  there  is  usually,  first  an  inspiration,  as  in  the  case  of 
coughing,  sneezing,  and  vomiting  ;  the  glottis  is  then  closed,  and  the 
diaphragm  fixed.  The  abdominal  muscles  are  contracted  as  in  expira- 
tion ;  but  as  the  glottis  is  closed,  the  whole  of  their  pressure  is  exercised 
on  the  abdominal  contents.  The  sphincter  of  the  rectum  being  relaxed, 
the  evacuation  of  its  contents  takes  place  accordingly  ;  the  effect  being, 
of  course,  increased  by  the  peristaltic  action  of  the  intestine.  As  in  the 
other  actions  just  referred  to,  there  is  as  much  tendency  to  the  escape 
of  the  contents  of  the  lungs  or  stomach  as  of  the  rectum  ;  but  the  pres- 
sure is  relieved  only  at  the  orifice,  the  sphincter  of  which  instinctively 
or  involuntarily  yields. 

Nervous  Mechanism. — The  anal  sphincter  muscle  is  normally  in  a 


296  HANDBOOK   OF   PHYSIOLOGY. 

state  of  tonic  contraction.  The  nervous  centre  which  governs  this  con- 
traction is  probably  situated  in  the  lumbar  region  of  the  spinal  cord,  in- 
asmuch as  in  cases  of  division  of  the  cord  above  this  region  the  sphincter 
regains,  after  a  time,  to  some  extent  the  tonicity  which  is  lost  imme- 
diately after  the  operation.  By  an  effort  Of  the  will,  acting  through  the 
centre,  the  contraction  may  be  relaxed  or  increased.  In  ordinary  cases 
the  apparatus  is  set  in  action  by  the  gradual  accumulation  of  faeces  in  the 
sigmoid  flexure  and  rectum,  pressing  by  the  peristaltic  action  of  these 
parts  of  the  large  intestine  against  the  sphincter,  and  causing  by  reflex 
action  its  relaxation  ;  this  sensory  impulse  acting  through  the  brain  and 
reflexly  through  the  spinal  centre. 

The  Gases  contained  in  the  Stomach  and  Intestines. — Under 
ordinary  circumstances,  the  alimentary  canal  contains  a  considerable 
quantity  of  gaseous  matter.  Any  one  who  has  had  occasion,  in  a  post- 
mortem examination,  either  to  lay  open  the  intestines,  or  to  let  out  the 
gas  which  they  contain,  must  have  been  struck  by  the  small  space  after- 
wards occupied  by  the  bowels,  and  by  the  large  degree,  therefore,  in 
which  the  gas,  which  naturally  distends  them,  contributes  to  fill  the 
cavity  of  the  abdomen.  Indeed,  the  presence  of  air  in  the  intestines  is 
so  constant,  and,  within  certain  limits,  the  amount  in  health  so  uniform, 
that  there  can  be  no  doubt  that  its  existence  here  is  not  a  mere  accident, 
but  intended  to  serve  a  definite  and  important  purpose,  although,  proba- 
bly, a  mechanical  one. 

Sources. — The  sources  of  the  gas  contained  in  the  stomach  and 
bowels  may  be  thus  enumerated  i — 

1.  Air  introduced  in  the  act  of  swallowing  either  food  or  saliva;  2. 
Gases  developed  by  the  decomposition  of  alimentary  matter,  or  of  the  se- 
cretions and  excretions  mingled  with  it  in  the  stomach  and  intestines ; 
3.  It  is  probable  that  a  certain  mutual  interchange  occurs  between  the 
gases  contained  in  the  alimentary  canal,  and  those  present  in  the  blood 
of  these  gastric  and  intestinal  blood-vessels  ;  but  the  conditions  of  the 
exchange  are  not  known,  and  it  is  very  doubtful  whether  anything  like 
a  true  and  definite  secretion  of  gas  from  the  blood  into  the  intestines  or 
stomach  ever  takes  place.  There  can  be  no  doubt,  however,  that  the  in- 
testines may  be  the  proper  excretory  organs  for  many  odorous  and  other 
substances,  either  absorbed  from  the  air  taken  into  the  lungs  in  inspira- 
tion, or  absorbed  in  the  upper  part  of  the  alimentary  canal,  again  to  be 
excreted  at  a  portion  of  the  same  tract  lower  down — in  either  case  as- 
suming rapidly  a  gaseous  form  after  their  excretion,  and  in  this  way, 
perhaps,  obtaining  a  more  ready  egress  from  the  body.  It  is  probable 
that,  under  ordinary  circumstances,  the  gases  of  the  stomach  and  intes- 
tines are  derived  chiefly  from  the  second  of  the  sources  which  have  been 
enumerated. 

It  is  now  very  generally  admitted  that  the  decompositions  of  food  in 
the  alimentary  canal  are  partially  the  result  of  the  growth  of  various 
kinds  of  micro-organisms,  some  of  which  have  been  already  mentioned, 
and  that  these  decompositions  are  independent  of  as  well  as  distinct  from 


DIGESTION. 


297 


the  action  of  the  digestive  fluids.     It  is  to  these  special  fermentative 
changes  that  the  gases  in  the  intestines  are  chiefly  due. 


Composition  of  Gases  contained  in  the  Alimentary  Canal. 
(Tabulated  from  various  authorities  by  Brinton.) 


Composition  by  Volume. 

Wnence  obtained. 

Oxygen. 

Nitrog. 

Carbon. 
Acid. 

14 
30 
12 
57 
43 
41 

Hydrog. 

4 

38 

8 

6 

19 

Carburet. 
Hydrogen. 

Sulphuret. 
Hydrogen. 

Stomach 

11 

71 
32 
66 
35 
46 
22 

13 

8 

11 

19 

Small  Intestines 

>  trace. 

Colon 

Expelled  per  anum 

CHAPTER    VIII. 

ABSORPTION. 

The  process  of  Absorption  has,  for  one  of  its  objects,  the  introduc- 
tion into  the  blood  of  fresh  materials  from  the  food  and  air,  and  of 
whatever  comes  into  contact  with  the  external  or  internal  surfaces  of  the 
body;  and,  for  another,  the  gradual  removal  of  parts  of  the  body  itself, 
when  they  need  to  be  renewed.  In  absorption  from  without  and  absorp- 
tion from  within,  the  process  manifests  some  variety,  and  a  very  wide 
range  of  action;  and  in  both  two  sets  of  vessels  are,  or  may  be,  con- 
cerned, namely,  the  Blood-vessels,  and  the  Lymph-vessels  or  Lymphatics 
to  which  the  term  Absorbents  has  been  specially  applied. 

Lymphatic  Vessels. 

Distribution. — The  principal  vessels  of  the  lymphatic  system  are,  in 
structure  and  general  appearance,  like  very  small  and  thin-walled  veins. 
They  are  provided  with  valves.  They  commence  in  fine  microscopic 
lymph-capillaries,  in  the  organs  and  tissues  of  the  body,  and  they  end 
directly  or  indirectly  in  two  trunks  which  open  into  the  large  veins  near 
the  heart  (Fig.  214).  The  lymph  and  chyle  which  they  contain,  unlike 
the  blood,  pass  only  in  one  direction,  namely,  from  the  fine  branches  to 
the  trunk  and  so  to  the  large  veins,  on  entering  which  they  are  mingled 
with  the  stream  of  blood,  and  form  part  of  its  constituents.  Eemem- 
bering  the  course  of  the  fluid  in  the  lymphatic  vessels,  viz.,  its  passage 
in  the  direction  only  towards  the  large  veins  in  the  neighborhood  of  the 
heart,  it  will  readily  be  seen  from  Fig.  214  that  the  greater  part  of  the 
contents  of  the  lymphatic  system  of  vessels  passes  through  a  compara- 
tively large  trunk  called  the  thoracic  duct,  which  finally  empties  its 
contents  into  the  blood-stream,  at  the  junction  of  the  internal  jugular 
and  subclavian  veins  of  the  left  side.  There  is  a  smaller  duct  on  the 
right  side.  The  lymphatic  vessels  of  the  intestinal  canal  are  called  lac- 
teals,  because  during  digestion,  the  fluid  contained  in  them  resembles 
milk  in  appearance;  and  the  lymph  in  the  lacteals  during  the  period  of 
digestion  is  called  chyle.  There  is  no  essential  distinction,  however, 
between  lacteals  and  lymphatics.  In  some  parts  of  their  course  all 
lymphatic  vessels  pass  through  certain  bodies  called  lymphatic  glands. 


ABSORPTION. 


299" 


Lymphatic  vessels  are  distributed  in  nearly  all  parts  of  the  body. 
Their  existence,  however,  has  not  yet  been  determined  in  the  placenta, 
the  umbilical  cord,  the  membranes  of  the  ovum,  or  in  any  of  the  so-called 
non-vascular  parts,  as  the  nails,  cuticle,  hair,  and  the  like. 

Origin  of  Lymph  Capillaries. — The  lymphatic  capillaries  commence 
most  commonly  either  (a)  in  closely-meshed  networks,  or  (b)  in  irregu- 
lar lacunar  spaces  between  the  various  structures  of  which  the  different 


Lymphatics  of  head   and 
neck,  right. 

Right  internal  jugular  vein. 
Right  subclavian  vein. 

Lymphatics  of  right  arm. 


Receptaculum  chyli. 


Lymphatics  of  lower  ex- 
tremities. 


Lymphatics    of   head  and 
neck,  left. 

Thoracic  duct. 
Left  subclavian  vein 


Thoracic  duct. 


Lacteals. 


Lympathics   of  lower  ex- 
tremities. 


Fig.  214.— Diagram  of  the  principal  groups  of  Lymphatic  vessels  (from  Quain). 

organs  are  composed.  Such  irregular  spaces,  forming  what  is  now 
termed  the  lymph-canalicular  system,  have  been  shown  to  exist  in  many 
tissues.  In  serous  membranes,  such  as  the  omentum  and  mesentery, 
they  occur  as  a  connected  system  of  very  irregular  branched  spaces 
partly  occupied  by  connective-tissue  corpuscles,  and  both  in  these  and 
in  many  other  tissues  are  found  to  communicate  freely  with  regular 
lymphatic  vessels.  In  many  cases,  though  they  are  formed  mostly  by 
the  chinks  and  crannies  between  the  blood-vessels,  secreting  ducts,  and 
other  parts  which  may  happen  to  form  the  framework  of  the  organ  in 
which  they  exist,  they  are  lined  by  a  distinct  layer  of  endothelium. 


300  HANDBOOK    OF    PHYSIOLOGY. 

The  lacteals  offer  an  illustration  of  another  mode  of  origin,  namely, 
(c)  in  blind  dilated  extremities;  but  there  is  no  essential  difference  in 
structure  between  these  and  the  lymphatic  capillaries  of  other  parts. 

Structure  of  Lymph  Capillaries. — The  structure  of  lymphatic  capil- 
laries is  very  similar  to  that  of  blood- capillaries:  their  walls  consist  of  a 
single  layer  of  endothelial  cells  of  an  elongated  form  and  sinuous  out- 
line, which  cohere  along  their  edges  to  form  a  delicate  membrane. 
They  differ  from  blood-capillaries  mainly  in  their  larger  and  very  vari- 
able calibre,  and  in  their  numerous  communications  with  the  spaces  of 
the  lymph-canalicular  system. 

Comnmnications  of  the  Lymphatics. — The  fluid  part  of  the  blood 
constantly  exudes  from  or  is  strained  through  the  walls  of  the  blood- 


Fig.  215.— Lymphatics  of  central  tendon  of  rabbit's  diaphragm,  stained  with  silver  nitrate. 
The  ground  substance  has  been  shaded  diagrammatically  to  bring  out  the  lymphatics  clearly.  I. 
Lymphatics  lined  by  long  narrow  endothelial  cells,  and  showing  v.  valves  at  frequent  intervals. 
(Schofleld.) 

capillaries,  so  as  to  moisten  all  the  surrounding  tissues,  and  occupies  the 
interspaces  which  exist  among  their  different  elements,  which  form  the 
beginnings  of  the  lymph-capillaries;  and  the  latter,  therefore,  are  the 
means  of  collecting  the  exuded  blood  plasma,  and  returning  that  part 
which  is  not  directly  absorbed  by  the  tissues  into  the  blood-stream.  It 
is  not  necessary  to  assume  the  presence  of  any  special  channels  between 
the  blood  and  lymphatic  vessels,  inasmuch  as  even  blood-corpuscles  can 
pass  bodily,  without  much  difficult}',  through  the  walls  of  the  blood- 
capillaries  and  small  veins,  and  could  pass  with  still  less  trouble,  prob- 
ably, through  the  comparatively  ill-defined  walls  of  the  capillaries  which 
contain  lymph. 

It  has  been  already  mentioned  that  in  certain  parts  of  the  body,  open- 


ABSOKPTION. 


301 


ings  or  stomata  exist,  by  which  lymphatic  capillaries  directly  communi- 
cate with  parts  hitherto  supposed  to  be  closed  cavities. 

When  absorption  into  the  lymphatic  system  takes  place  in  membranes 
covered  by  epithelium  or  endothelium  through  the  interstitial  or  inter- 
cellular cement-substance,  it  is  said  to  take  place  through,  psetido  stomata, 
already  alluded  to. 


Fig.  216.—  Lymphatic  vessels  of  the  head  and  neck  and  the  upper  part  of  the  trank  (MaseagnD. 
1/6.  —The  chest  and  pericardium  have  been  opened  on  the  lett  side,  and  the  left  mamma  detached 
and  thrown  outwards  over  the  left  arm,  so  as  to  expose  a  great  part  of  its  deep  surface.  The  prin- 
cipal lymphatic  vessels  and  glands  are  shown  on  the  side  of  the  head  and  face,  and  in  the  neck 
axilla,  and  mediastinum.  Between  the  left  internal  jugular  vein  and  the  common  carotid  artery, 
the  upper  ascending  part  of  the  thoracic  duct  marked  l,  and  above  this,  and  descending  to  2.  the 
arch  and  last  part  of  the  duct.  The  termination  of  the  upper  lymphatics  of  the  diaphragm  in  the 
mediastinal  glands,  as  well  as  the  cardiac  and  the  deep  mammary  lymphatics,  is  also  shown. 

Demonstration  of  Lymphatics  of  Diaphragm. — The  stomata  on  the 
peritoneal  surface  of  the  diaphragm  are  the  openings  of  short  vertical 
canals  which  lead  up  into  the  lymphatics,  and  are  lined  by  cells  like  those 
of  germinating  endothelium.  By  introducing  a  solution  of  Berlin  blue 
into  the  peritoneal  cavity  of  an  animal  shortly  after  death,  and  suspend- 
ing it,  head  downwards,  an  injection  of  the  lymphatic  vessels  of  the 
diaphragm,  through  the  stomata  on  its  peritoneal  surface,  may  readily 
be  obtained,  if  artificial  respiration  be  carried  on  for  about  hall  an  hour. 
In  this  way  it  has  been  found  that  in  the  rabbit  the  lymphatics  are  ar- 
ranged between  the  tendon  bundles  of  the  centrum  tendinenm;  and  they 
are  hence  termed  interfascicular.     The  centrum  tendineum  is  coated  by 


302 


HANDBOOK    OF    PHYSIOLOGY. 


consists  ot  tendon  bundles  arranged  m  concentric  rings  towards   the 
Pleural  «de  and  m  radiating  bundles  towards  the  peritonei  side 

The  lymphatics  of  the  anterior  half  of  the  diaphragm  open  into 
those  of  the  anterior  mediastinum,  while  those  of  the  posterior half  ™« 
into  a  lymphatic  vessel  in  the  posterior  mediastinum!  which  soon  enC 
the  thoracic  duct  Both  these  sets  of  vessels,  and  the  elands  into  which 
they  pass,  are  readily  injected  by  the  method 'above  delribedjSnd^ 


"Ilil 

'II 


Fig.  217. 


Fig.  218. 


glan^t^  V5.-5.  Two  small 

arch  of  lymphatics.    9,  9'.  Outer™  d  inne?  sets :  nf ?=Sb     ?  n     lymphatic  vessels.  8,  8.  Palmar- 
Median  vein  /  Ulnar  vein   The  lvmr  hS^JZtJSL      f  ,-    V  peP1^0  vein,    d.  Radial  vein.    e. 
.    Fig-  ■ajrK5SK3v3ifi5S8!^^  (Mascagni, 

glands.    2,  2'.  Lower  inguinal  or  femoral  IibtiHo ,     a  a/   "ii        Par,c  OI  taJgh,  1/b.    1.  Upper  inguinal 
long  saphenous  vein.     ( Mascagni;  g  3'  3  '  PlexUS  of  lymphatics  in  the  course  of  the 

can  be  little  doubt  that  during  life  the  flow  of  lymph  along  these  chan- 
nels is  chiefly  caused  by  the  action  of  the  diaphragm  dunnf  rapfrati™ 
As  it  descends  m  inspiration,  the  spaces  between" the  radiating  tendon 


absorption.  303 

bundles  dilate,  and  lymph  is  sucked  from  the  peritoneal  cavity,  through 
the  widely  open  stomata,  into  the  interfascicular  lymphatics.  During 
expiration,  the  spaces  between  the  concentric  tendon  bundles  dilate,  and 
the  lymph  is  squeezed  into  the  lymphatics  towards  the  pleural  surface 
(Klein).  It  thus  appears  probable  that  during  health  there  is  a  con- 
tinued sucking  in  of  lymph  from  the  peritoneum  into  the  lymphatics 
by  the  "  pumping"  action  of  the  diaphragm;  and  there  is  doubtless  an 
equally  continuous  exudation  of  fluid  from  the  general  serous  surface  of 
the  peritoneum.  When  this  balance  of  transudation  and  absorption  is 
disturbed  either  by  increased  transudation  or  some  impediment  to  absorp- 
tion, an  accumulation  of  fluid  necessarily  take  place  (ascites). 

Stomata  have  been  found  in  the  pleura;  and  as  they  maybe  presumed 
to  exist  in  other  serous  membranes,  it  would  seem  as  if  the  serous  cavi- 
ties, hitherto  supposed  closed,  form  but  a  large  lymph-sinus  or  widening 
out,  so  to  speak,  of  the  lymph-capillary  system  with  which  they  directly 
communicate. 


Fig.  219.— Peritoneal  surface  of  septum  cisternal  lymphaticae  magnee  of  frog.  The  stomata, 
some  of  which  are  open,  some  collapsed,  are  surrounded  by  germinating  endothelium.  \  160. 
(Klein.) 

Structure  of  Lymphatic  Vessels. — The  larger  vessels  are  very  like 
veins,  having  an  external  coat  of  fibro-cellular  tissue,  with  elastic  fila- 
ments; within  this,  a  thin  layer  of  fibro-cellular  tissue,  with  plain  muscu- 
lar fibres,  which  have,  principally,  a  circular  direction,  and  are  much 
more  abundant  in  the  small  than  in  the  larger  vessels;  and  again,  within 
this,  an  inner  elastic  layer  of  longitudinal  fibres,  and  a  lining  of  epithe- 
lium; and  numerous  valves.  The  valves,  constructed  like  those  of  veins, 
and  with  the  free  edges  turned  towards  the  heart,  are  usually  arranged 
in  pairs,  and,  in  the  small  vessels,  are  so  closely  placed,  that  when  the 
vessels  are  full,  the  valves  constricting  them  where  their  edges  are  at- 
tached, give  them  a  peculiar  beaded  or  knotted  appearance. 

Current  of  the  Lymph. —With  the  help  of  the  valvular  mechanism 
(1)  all  occasional  pressure  on  the  exterior  of  the  lymphatic  and  lacteal 
vessels  propels  the  lymph  towards  the  heart:  thus  muscular  and   other 


304  HANDBOOK    OF  PHYSIOLOGY. 

external  pressure  accelerates  the  flow  of  the  lymph  as  it  does  that  of  the 
blood  in  the  veins.  The  actions  of  (2)  the  muscular  fibres  of  the  small 
intestine,  and  probably  the  layer  of  unstriped  muscle  present  in  each  in- 
testinal villus,  seem  to  assist  in  propelling  the  chyle:  for,  in  the  small 
intestine  of  a  mouse,  the  chyle  has  been  seen  moving  with  intermittent 
propulsions  that  appeared  to  correspond  with  the  peristaltic  movements 
of  the  intestine.  But  for  the  general  propulsion  of  the  lymph  and 
chyle,  it  is  probable  that,  together  with  (3)  the  visa  tergo  resulting  from 
absorption  (as  in  the  ascent  of  sap  in  a  tree),  and  from  external  pressure, 
some  of  the  force  may  be  derived  (4)  from  the  contractility  of  the  ves- 
sel's own  walls.  The  respiratory  movements,  also,  (5)  favor  the  current 
of  lymph  through  the  thoracic  duct  as  they  do  the  current  of  blood  in 
the  thoracic  veins. 

Lymph-Hearts. — In  reptiles  and  some  birds,  an  important  auxiliary 
to  the  movement  of  the  lymph  and  chyle  is  supplied  in  certain  muscular 
sacs,  named  lyrnph-Jiearts  (Fig.  220),  and  it  has  been  shown  that  the 


Fig.  220.— Lymphatic  heart  (9  lines  long,  4  lines  broad)  of  a  large  species  of  serpent,  the  Python 
bivittatus.  4.  The  external  cellular  coat.  5.  The  thick  muscular  coat.  Four  muscular  columns 
run  across  its  cavity,  which  communicates  with  three  lymphatics  (1—  only  one  is  seen  here),  and 
with  two  veins  (2,  2).  6.  The  smooth  lining  membrane  of  the  cavity.  7.  A  small  appendage,  or 
auricle,  the  cavity  of  which  is  continuous  with  that  of  the  rest  of  the  organ  (after  E.  Weber). 

caudal  heart  of  the  eel  is  a  lymph-heart  also.  The  number  and  position 
of  these  organs  vary.  In  frogs  and  toads  there  are  usually  four,  two  an- 
terior and  two  posterior;  in  the  frog,  the  posterior  lymph-heart  on  each 
side  is  situated  in  the  ischiatic  region,  just  beneath  the  skin;  the  anterior 
lies  deeper,  just  over  the  transverse  process  of  the  third  vertebra.  Into 
each  of  these  cavities  several  lymphatics  open,  the  orifices  of  the  vessels 
being  guarded  by  valves,  which  prevent  the  retrograde  passage  of  the 
lymph.  From  each  heart  a  single  vein  proceeds,  and  conveys  the  lymph 
directly  into  the  venous  system.  In  the  frog,  the  inferior  lymphatic 
heart,  on  each  side,  pours  its  lymph  into  a  branch  of  the  ischiatic  vein; 
by  the  superior,  the  lymph  is  forced  into  a  branch  of  the  jugular  vein, 
which  issues  from  its  anterior  surface,  and  which  becomes  turgid  each 
time  that  the  sac  contracts.  Blood  is  prevented  from  passing  from  the 
vein  into  the  lymphatic  heart  by  a  valve  at  its  orifice. 

The  muscular  coat  of  these  hearts  is  of  variable  thickness;  in  some 
cases  it  can  only  be  discovered  by  means  of  the  microscope;  but  in  every 
case  it  is  composed  of  striped  fibres.     The  contractions  of  the  hearts  are 


ABSORPTION. 


305 


rhythmical,  occurring  about  sixty  times  in  a  minute,  slowly,  and,  in 
comparison  with  those  of  the  blood-hearts,  feebly.  The  pulsations'  of  the 
cervical  pair  are  not  always  synchronous  with  those  of  the  pair  in  the 
ischiatic  region,  and  even  the  corresponding  sacs  of  opposite  sides  are 
not  always  synchronous  in  their  action. 

Unlike  the  contractions  of  the  blood-heart,  those  of  the  lymph-heart 
appear  to  be  directly  dependent  upon  a  certain  limited  portion  of  the 
spinal  cord.  For  Volkmann  found  that  so  long  as  the  portion  of  spinal 
cord  corresponding  to  the  third  vertebra  of  the  frog  was  uninjured,  the 
cervical  pair  of  lymphatic  hearts  continued  pulsating  after  all  the  rest 
of  the  spinal  cord  and  the  brain  were  destroyed;  while  destruction  of 
this  portion,  even  though  all  other  parts  of  the  nervous  centres  were  un- 
injured, instantly  arrested  the  heart's  movements.  The  posterior,  or 
ischiatic,  pair  of  lymph-hearts  were  found  to  be  governed,  in  like  man- 
ner, by  the  portion  of  spinal  cord  corresponding  to  the  eighth  vertebra. 
Division  of  the  posterior  spinal  roots  did  not  arrest  the  movements;  but 
division  of  the  anterior  roots  caused  them  to  cease  at  once. 

Lymphatic  Glands. 

Lymphatic  glands  are  small  round  or  oval  compact  bodies  varying  in 
size  from  a  hempseed  to  a  bean,  interposed  in  the  course  of  lymphatic 


Fig.  221. 


Fig.  222. 


Fig.  221.— Section  of  a  mesenteric  gland  from  the  ox,  slightly  magnified,  a,  Hilus;  b  ( in  the  cen- 
tral part  of  the  figure),  medullary  substance;  c,  cortical  substance  with  indistinct  alveoli;  d,  cap- 
sule.   I  Ki'lliker.) 

Fig.  222.— Section  of  medullary  substance  of  an  inguinal  gland  of  an  ox:  a,  n,  glandular  sub- 
stance or  pulp  forming  rounded  cords  joining  in  a  continuous  net  (dark  in  the  figure ) ;  c,  c.  trabee- 
ulse;  the  space,  b,  b,  between  these  and  the  glandular  substance  is  the  lymph  sinus,  washed  clear  of 
corpuscles  and  traversed  by  filaments  of  retiform  connective  tissue,     x  90.    (  KOlliker.) 


vessels,  and  through  which  the  chief  part  of  the  lymph  passes  in  its 
course  to  be  discharged  into  the  blood-vessels.  They  are  found  in  great 
numbers  iu  the  mesentery,  and  along  the  great  vessels  of  the  abdomen, 
thorax,  and  neck;  in  the  axilla  and  groin;  a  few  in  the  popliteal  space, 
but  not  further  down  the  leg,  and  in  the  arm  as  fur  as  the  elbow.  Some 
20 


306 


HANDBOOK    OF    PHYSIOLOGY. 


tymphatics  do  not,  however,  pass  through  glands  before  entering  the 
thoracic  duct. 

Structure. — A  lymphatic  gland  is  covered  externally  by  a  capsule  of 
connective  tissue,  generally  containing  some  unstriped  muscle.  At  the 
inner  side  of  the  gland,  which  is  somewhat  concave  {hilus),  (Fig.  221  a), 
the  capsule  sends  inwards  processes  called  trabecule®  in  which  the  blood- 
vessels are  contained,  and  these  join  with  other  processes  prolonged  from 
the  inner  surface  of  the  part  of  the  capsule  covering  the  convex  or  outer 
part  of  the  gland;  they  have  a  structure  similar  to  that  of  the  capsule, 
and  entering  the  gland  from  all  sides,  and  freely  communicating,  form 
a  fibrous  supporting  stroma.  The  interior  of  the  gland  is  seen  on  sec- 
tion, even  when  examined  with  the  naked  eye,  to  be  made  up  of  two 


Fig.  223.— Diagrammatic  section  of  lymphatic  gland,  a.  I.,  afferent;  el.,  efferent  lymphatics; 
C,  cortical  substance ;  I. h.,  reticulating  cords  of  medull  iry  substance;  l.s.,  lymph-sinus;  c,  fibrous 
coat  sending  in  trabeculse,  t.r.,  into  the  substance  of  the  gland.    (Sharpey.)       «•     ■ 

parts,  an  outer  or  cortical  (Fig.  221,  c,  c),  which  is  light  colored,  and  an 
inner  of  redder  appearance,  the  medullary  portion  (Fig.  221).  In  the 
outer  or  cortical  part  of  the  gland  (Fig.  223)  the  intervals  between  the 
trabeculse  are  comparatively  large,  and  form  more  or  less  triangular  in- 
tercommunicating spaces  termed  alveoli ;  whilst  in  the  more  central  or 
medullary  part  is  a  finer  meshwork  formed  by  the  more  free  anastomosis 
of  the  trabecular  processes.  Within  the  alveoli  of  the  cortex  and  in  the 
meshwork  formed  by  the  trabecular  in  the  medulla,  is  contained  the 
proper  gland  structure.  In  the  former  it  is  arranged  as  follows:  occu- 
pying the  central  and  chief  part  of  each  alveolus,  is  a  more  or  less 
wedge-shaped  mass  of  adenoid  tissue,  densely  packed  with  lymph  cor- 
puscles ;  but  at  the  periphery  surrounding  the  central  portion  and  im- 


ABSORPTION. 


307 


mediately  next  the  capsule  and  trabecular  is  a  more  open  mesh  work  of 
adenoid  tissue  constituting  the  lymph  sinus  or  channel,  and  containing 
fewer  lymph  corpuscles.  The  central  mass  is  inclosed  in  endothelium, 
the  cells  of  which  join  by  their  processes,  the  processes  of  the  adenoid 
framework  of  the  lymph  sinus.  The  trabecular  are  also  covered  with 
endothelium.  The  lining  of  the  central  mass  does  not  prevent  the  pas- 
sage of  fluids  and  even  of  corpuscles  into  the  lymph  sinus.  The  frame- 
work of  the  adenoid  tissue  of  the  lymph  sinus  is  nucleated,  that  of  the 
central  mass  is  non-nucleated.  At  the  inner  part  of  the  alveolus,  the 
wedge-shaped  central  mass  divides  into  two  or  more  smaller  rounded  or 
cord-like  masses  which  joining  with  those  from  the  other  alveoli,  forma 
much  closer  arrangement  of  the  gland  tissue  than  in  the  cortex;  spaces 


Fig.  224.— A  small  portion  of  medullary  substance  from  a  mesenteric  gland  of  the  ox.  d,  d, 
trabecules;  a,  part  of  a  cord  of  glandular  substances  from  which  all  but  a  few  of  the  lymph-corpus- 
cles have  been  washed  out  to  show  its  supporting  meshwork  of  retif orm  tissue  and  its  capillary 
blood-vessels (.which  have  been  in jected,  and  are  dark  in  the  figure);  b,  b,  lymph  sinus,  of  which 
the  retif  orm  tissue  is  represented  only  at  c,  c.     X  800.    tKolliker. ) 

(Fig.  223  h),  are  left  within  those  anastomosing  cords,  in  winch  are 
found  portions  of  the  trabecular  meshwork  and  the  continuation  of  the 
lymph  sinus. 

The  essential  structure  of  lymphatic-gland  substance  resembles  that 
which  was  described  as  existing,  in  a  simple  form,  in  the  interior  of  the 
solitary  and  agmiuated  intestinal  follicles. 

The  lymph  enters  the  glaud  by  several  afferent  vessels,  which  open 
beneath  the  capsule  into  the  lymph-channel  or  lymph-path;  at  the  same 
time  they  lay  aside  all  their  coats  except  the  endothelial  lining,  which 
is  continuous  with  the  lining  of  the  lymph-path.     The  efferent  vessels 


308  HANDBOOK    OF    PHYSIOLOGY. 

begin  in  the  medullary  part  of  the  gland,  and  are  continuous  with  the 
lymph-path  here  as  the  afferent  vessels  were  with  the  cortical  portion; 
the  endothelium  of  one  is  continuous  with  that  of  the  other. 

The  efferent  vessels  leave  the  gland  at  the  hilus,  the  more  or  less 
concave  inner  side  of  the  gland,  and  generally  either  at  once  or  very 
soon  after  join  together  to  form  a  single  vessel. 

Blood-vessels  which  enter  and  leave  the  gland  at  the  hilus  are  freely 
distributed  to  the  trabecular  tissue  and  to  the  gland-pulp. 

The  Lymph  and  Chyle. 

Lymph  is,  under  ordinary  circumstances,  a  clear,  transparent,  and 
yellowish  fluid.  It  is  devoid  of  smell,  is  slightly  alkaline,  and  has  a 
saline  taste.  As  seen  with  the  microscope  in  the  small  transparent  ves- 
sels of  the  tail  of  the  tadpole,  it  usually  contains  no  corpuscles  or  par- 
ticles of  any  kind;  and  it  is  only  in  the  larger  trunks  that  any  corpuscles 
are  to  be  found.  These  corpuscles  are  similar  to  colorless  blood-cor- 
puscles. The  fluid  in  which  the  corpuscles  float  is  albuminous,  and  con- 
tains no  fatty  particles;  but  is  liable  to  variations  according  to  the 
general  state  of  the  blood,  and  to  that  of  the  organ  from  which  the 
lymph  is  derived.  As  it  advances  towards  the  thoracic  duct,  after  pass- 
ing through  the  lymphatic  glands,  it  becomes  spontaneously  coagulable 
and  the  number  of  corpuscles  is  much  increased. 

Chyle,  found  in  the  lacteals  after  a  meal,  is  an  opaque,  whitish, 
milky  fluid,  neutral  or  slightly  alkaline  in  reaction.  Its  whiteness  and 
opacity  are  due  to  the  presence  of  innumerable  particles  of  oily  or  fatty 
matter,  of  exceedingly  minute  though  nearly  uniform  size,  measuring 
on  the  average  about  ^i^  of  an  inch.  These  constitute  what  is  termed 
the  molecular  base  of  chyle.  Their  number,  and  consequently  the 
opacity  of  the  chyle,  are  dependent  upon  the  quantity  of  fatter  matter 
contained  in  the  food.  The  fatty  nature  of  the  molecules  is  made  mani- 
fest by  their  solubility  in  ether.  Each  molecule  probably  consists  of  a 
droplet  of  oil  coated  over  with  albumen,  in  the  manner  in  which  minute 
drops  of  oil  always  become  covered  in  an  albuminous  solution.  This  is 
proved  when  water  or  dilute  acetic  acid  is  added  to  chyle,  many  of  the 
molecules  are  lost  sight  of,  and  oil-drops  appear  in  their  place,  as  the 
investments  of  the  molecules  have  been  dissolved,  and  their  oily  contents 
have  run  together. 

Except  these  molecules,  the  chyle  taken  from  the  villi  or  from  lac- 
teals near  them,  contains  no  other  solid  or  organized  bodies.  The  fluid 
in  which  the  molecules  float  is  albuminous  and  does  not  spontaneously 
coagulate.  But  as  the  chyle  passes  on  towards  the  thoracic  duct,  and 
especially  whilst  traversing  one  or  more  of  the  mesenteric  glands,  it  is 
elaborated.  The  quantity  of  molecules  and  oily  particles  gradually  di- 
minishes; cells,  to  which  the  name  of  chyle-corpuscles  is  given,  appear  in 


ABSORPTION.  309 

it;  and  it  acquires  the  property  of  coagulating  spontaneously.  The 
higher  in  the  thoracic  duct  the  chyle  advances,  the  greater  is  the  num- 
ber of  chyle-corpuscles,  and  the  larger  and  firmer  is  the  clot  which  forms 
in  it  when  withdrawn  and  left  at  rest.  Such  a  clot  is  like  one  of  blood 
without  the  red  corpuscles,  having  the  chyle-corpuscles  entangled  in  it, 
and  the  fatty  matter  forming  a  white  creamy  film  on  the  surface  of  the 
serum.  But  the  clot  of  chyle  is  softer  and  moister  than  that  of  blood. 
Like  blood,  also,  the  chyle  often  remains  for  a  long  time  in  its  vessels 
without  coagulating,  but  coagulates  rapidly  on  being  removed  from  them. 
The  existence  of  the  materials  which,  by  their  union  form  fibrin,  is  there- 
fore, certain;  and  their  increase  appears  to  be  commensurate  with  that  of 
the  corpuscles. 

The  structure  of  the  chyle-corpuscles  was  described  when  speaking  of 
the  white  corpuscles  of  the  blood,  with  which  they  are  identical.  The 
lymph,  in  chemical  composition,  resembles  diluted  plasma,  and  from 
what  has  been  said,  it  will  appear  that  perfect  chyle  and  lymph  are,  in 
essential  characters,  nearly  similar,  and  scarcely  differ,  except  in  the 
■preponderance  of  fatty  and  proteid  matter  in  the  chyle. 

Chemical  Composition  of  Lymph  and  Chyle  (Owen  Rees). 

I.  II.  III. 

Lymph  Chyle      Mixed  Lymph  & 

(Donkey.)       (Donkey).  Chyle  (Human). 

Water, 96.536     690.237         90.48 

Solids,  3.454         9.763  9.52 

Solids— 

Proteids     including    Serum-Albu- >       3g  3>886  ^QS 

mm,   fibrinogen,  and  Globulin.  \ 

Extractives,  including  in  (i  and  n)  )    -,  c-n         ,  ~a.  inQ 

Q  tt       t        •    jLnu  i    *    ■      r   l.oo9         I.060  .10b 

bugar,  Urea, Leu cin  &  (Jholesterm,  \ 

Fatty  matter,  ....     a  trace         3.601  .92 

Salts, 585  .711  .44 

Quantity. — The  quantity  which  would  pass  into  a  cat's  blood  in 
twenty-four  hours  has  been  estimated  to  be  equal  to  about  one-sixth  of 
the  weight  of  the  whole  body.  And,  since  the  estimated  weight  of  the 
blood  in  cats  is  to  the  weight  of  their  bodies  as  1  to  7,  the  quantity  of 
lymph  daily  traversing  the  thoracic  duct  would  appear  to  be  about  equal 
to  the  quantity  of  blood  at  any  time  contained  in  the  animals.  By 
another  series  of  experiments,  the  quantity  of  lymph  traversing  the  tho- 
racic duct  of  a  dog  in  twenty-four  hours  was  found  to  be  about  equal  to 
two-thirds  of  the  blood  in  the  body. 

The  Process  of  Absorption. 
(a.)  By  the  Lacteals. — During  the  passage  of  the  chyme  along  tin- 
intestinal  canal,  its  completely  digested  parts  are  absorbed  bj  the  blood- 


310  HANDBOOK    OF    PHYSIOLOGY: 

vessels  and  lacteals  distributed  in  the  mucous  membrane.  The  lacteals 
appear  to  absorb  only  certain  constituents  of  the  digested  food,  includ- 
ing particularly  the  fatty  portions.  The  absorption  by  both  sets  of 
vessels  is  carried  on  most  actively,  but  not  exclusively,  in  the  villi  of  the 
small  intestine  ;  for  in  these  minute  processes,  both  the  capillary  blood- 
vessels and  the  lacteals  are  brought  almost  into  contact  with  the  intes- 
tinal contents.  There  seems  to  be  no  doubt  that  absorption  of  fatty 
matters  during  digestion,  from  the  contents  of  the  intestines,  is  effected 
chiefly  between  the  epithelial  cells  which  line  the  intestinal  tract  (Wat- 
ney),  and  especially  those  which  clothe  the  surface  of  the  villi.  Thence, 
the  fatty  particles  are  passed  on  into  the  interior  of  the  lacteal  vessels, 
but  how  they  pass,  and  what  laws  govern  their  passage,  are  not  at  pres- 
ent exactly  known. 

The  process  of  absorption  is  assisted  by  the  pressure  exercised  on  the 
contents  of  the  intestines  by  their  contractile  walls  ;  and  the  absorption 
of  fatty  particles  is  also  facilitated  by  the  presence  of  the  bile,  and  the 
pancreatic  and  intestiual  secretions,  which  moisten  the  absorbing  sur- 
face. For  it  has  been  found  by  experiment,  that  the  passage  of  oil 
through  an  animal  membrane  is  made  much  easier  when  the  latter  is  im- 
pregnated with  an  alkaline  fluid. 

(b.)  By  the  Lymphatics. — The  real  source  of  the  lymph,  and  the 
mode  in  which  its  absorption  is  effected  by  the  lymphatic  vessels,  were 
long  matters  of  discussion.  But  the  problem  has  been  much  simplified 
by  more  accurate  knowledge  of  the  anatomical  relations  of  the  lymph- 
atic capillaries.  The  lymph  is,  as  has  been  pointed  out,  diluted  liquor 
sanguinis,  which  is  always  exuding  from  the  blood-capillaries  into  the 
interstices  of  the  tissues  in  which  they  lie  ;  and  as  these  interstices  form 
in  most  parts  of  the  body  the  beginnings  of  the  lymphatics,  the  source 
of  the  lymph  is  sufficiently  obvious.  In  connection  with  this  may  be 
mentioned  the  fact  that  changes  in  the  character  of  the  lymph  corre- 
spond very  closely  with  changes  in  the  character  of  either  the  whole  mass 
of  blood,  or  of  that  in  the  vessels  of  the  part  from  which  the  lymph  is 
exuded.  Thus  it  appears  that  the  coagulability  of  the  lymph,  although 
always  less  than,  is  directly  proportionate  to  that  of  the  blood  ;  and 
that  when  fluids  are  injected  into  the  blood-vessels  in  sufficient  quantity 
to  distend  them,  the  injected  substance  may  be  almost  directly  after- 
wards found  in  the  lymphatics. 

Some  other  matters  than  those  originally  contained  in  the  exuded 
liquor  sanguinis  may,  however,  find  their  way  with  it  into  the  lymphatic 
vessels.  Parts  which  having  entered  into  the  composition  of  a  tissue, 
and,  having  fulfilled  their  purpose,  require  to  be  removed,  may  not  be 
altogether  excrementitious,  but  may  admit  of  being  reorganized  and 
adapted  again  for  nutrition  ;  and  these  may  be  absorbed  by  the  lymph- 


ABSORPTION.  31 1 

atics,  and  elaborated  with  the  other  contents  of  the  lymph  in  passing 
through  the  glands. 

(c.)  By  Blood- Vessels. — In  the  absorption  by  the  lymphatic  or 
lacteal  vessels  just  described,  there  appears  something  like  the  exercise 
of  choice  in  the  materials  admitted  into  them.  But  the  absorption  by 
blood-vessels  presents  no  such  appearance  of  selection  of  materials ; 
rather,  it  appears,  that  every  substance,  whether  gaseous,  liquid,  or  a 
soluble,  or  minutely  divided  solid,  may  be  absorbed  by  the  blood-vessels, 
provided  it  is  capable  of  permeating  their  walls,  and  of  mixing  with  the 
blood  ;  and  that  of  all  such  substances,  the  mode  and  measure  of  ab- 
sorption are  determined  almost  solely  by  their  physical  or  chemical 
properties  aud  conditions,  and  by  those  of  the  blood  and  the  walls  of  the 
blood-vessels. 

Method  of  Absorption. 

(a.)  Osmosis. — The  phenomena  of  absorption  of  all  the  materials 
of  the  food  except  the  fats  are,  to  a  great  extent,  comparable  to  that 
passage  of  fluids  through  membrane,  which  occurs  quite 
independently  of  vital  conditions,  and  the  earliest  and  best 
scientific  investigation  of  which  was  made  by  Dutrochet. 
The  instrument  which  he  employed  in  his  experiments  was 
named  an  endosmometer.  It  may  consist  of  a  graduated 
tube  expanded  into  an  open-mouthed  bell  at  one  end,  over 
which  a  portion  of  membrane  is  tied  (Fig.  225).  If  now 
the  bell  be  filled  with  a  solution  of  a  salt — say  sodium  chlo- 
ride, and  be  immersed  in  water,  the  water  will  pass  into 
the  solution,  and  part  of  the  salt  will  pass  out  into  the 
water  ;  the  water,  however,  will  pass  into  the  solution 
much  more  rapidly  than  the  salt  will  pass  out  into  the 
water,  and  the  diluted  solution  will  rise  in  the  tube.  To 
this  passage  of  fluids  through  membrane  the  term  Osmosis 
is  applied. 

The  nature  of  the  membrane  used  as  a  septum,  and  its 
affinity  for  the  fluids  subjected  to  experiment  have  an  im- 
portant influence,  as  might  be  anticipated,  on  the  rapidity  Fig.  225.-E11- 
and  duration  of  the  osmotic  current.  Thus,  if  a  piece 
of  ordinary  bladder  be  used  as  the  septum  between  water  and  alcohol, 
the  current  is  almost  solely  from  the  water  to  the  alcohol,  on  account  of 
the  much  greater  affinity  of  water  for  this  kind  of  membrane  ;  while,  on 
the  other  hand,  in  the  case  of  a  membrane  of  caoutchouc,  the  alcohol, 
from  its  greater  affinity  for  this  substauce,  would  pass  freely  into  the 
water. 

Absorption  by  blood-vessels  is  the  consequence  of  their  walls  being, 
like  the  membranous  septum  of  the  endosmometer,  porous  and  capable 


313  HANDBOOK    OF    PHYSIOLOGY. 

of  imbibing  fluids,  and  of  the  blood  being  so  composed  that  most  fluids 
will  mingle  with  it.  Thus  the  relation  of  the  chyme  in  the  stomach 
and  intestines  to  the  blood  circulating  in  the  vessels  of  the  gastric  and 
intestinal  mucous  membrane  is  evidently  just  that  which  is  required  for 
osmosis.  The  chyme  contains  substances  which  have  been  so  acted 
upon  by  the  digestive  juices  as  to  have  become  quite  able  to  pass  through 
an  animal  membrane,  or  to  dialyze  as  it  is  called.  The  thin  animal  mem- 
brane is  the  coat  of  the  blood-vessels  with  the  intervening  mucous  mem- 
brane. The  nature  of  the  fluid  within  the  vessels,  the  very  feeble  power 
of  dialyzation  which  the  albuminous  blood  possesses,  determines  the  di- 
rection of  the  osmotic  current,  viz.,  into  and  not  out  of  the  blood-ves- 
sels. The  current  is  of  course  aided  by  the  fact  of  the  constant  change 
in  the  blood  presented  to  the  osmotic  surface,  as  it  rapidly  circulates 
within  the  vessels.  As  a  rule  the  current  is  from  the  stomach  or  intes- 
tine into  the  blood,  but  the  reversed  action  may  occur,  when,  for  ex- 
ample, a  certain  salt,  e.  g.,  sulphate  of  magnesia,  is  taken  into  the 
stomach,  in  which  case  there  is  a  rapid  discharge  of  water  from  the 
blood-vessels  into  the  alimentary  canal  resulting  in  purgation.  The 
presence  of  various  substances  in  the  food  has  the  power  of  diminishing 
the  rate  of  absorption,  their  influence  is  jorobably  exerted  upon  the  mem- 
brane, diminishing  its  power  of  permitting  osmosis.  Whereas  the  pres- 
ence of  a  little  hydrochloric  acid  in  the  contents  of  the  stomach  appears 
to  determine  the  direction  of  the  osmosis,  or  at  any  rate  to  diminish  or 
prevent  exosmosis. 

The  conditions  for  osmosis  exist  not  only  in  the  alimentary  mucous 
membrane,  but  also  in  the  serous  cavities  and  the  tissues  elsewhere. 

The  process  of  absorption,  in  an  instructive,  though  very  imperfect 
degree,  may  be  observed  in  any  portion  of  vascular  tissue  removed  from 
the  body.  If  such  a  one  be  placed  in  a  vessel  of  water,  it  will  shortly 
swell,  and  become  heavier  and  moister,  through  the  quantity  of  water 
imbibed  or  soaked  into  it;  and  if  now,  the  blood  contained  in  any  of  its 
vessels  be  let  out,  it  will  be  found  diluted  with  water,  which  has  been 
absorbed  by  the  blood-vessels  and  mingled  with  the  blood.  The  water 
round  the  piece  of  tissue  also  will  become  blood-stained;  and  if  all  be 
kept  at  perfect  rest,  the  stain  derived  from  the  solution  of  the  coloring 
matter  of  the  blood,  together  with  some  of  the  albumen  and  other  parts 
of  the  liquor  sanguinis,  will  spread  more  widely  every  day.  The  same 
will  happen  if  the  piece  of  tissue  be  placed  in  a  saline  solution  instead 
of  water,  or  in  a  solution  of  coloring  or  odorous  matter,  either  of  which 
will  give  their  tinge  or  smell  to  the  blood,  and  receive,  in  exchange,  the 
color  of  the  blood. 

Various  substances  have  been  classified  according  to  the  degree  in 
which  they  possess  the  property  of  passing,  when  in  a  state  of  solution 
in  water,  through  membrane;  those  which  pass  freely,  inasmuch  as  they 
are   usually  capable  of  crystallization,  being  termed  crystalloids,  and 


ABSORPTION.  313 

those  which  pass  with  difficulty,  on  account  of  their,  physically,  glue- 
like character,  colloids. 

This  distinction,  however,  between  colloids  and  crystalloids  which  is 
made  the  basis  of  their  classification,  is  by  no  means  the  only  difference 
between  them.  The  colloids,  besides  the  absence  of  power  to  assume  a 
crystalline  form,  are  characterized  by  their  inertness  as  acids  or  bases, 
and  feebleness  in  all  ordinary  chemical  relations.  Examples  of  them  are 
found  in  albumin,  gelatin,  starch,  hydrated  alumina,  hydrated  silicic 
acid,  etc.  ;  while  the  crystalloids  are  characterized  by  qualities  the  re- 
verse of  those  just  mentioned  as  belonging  to  colloids.  Alcohol,  sugar, 
and  ordinary  saline  substances  are  examples  of  crystalloids. 

(b.)  Filtration,  or  transudation.  A  distinction  must  be  drawn  be- 
tween osmosis  and  filtration.  The  latter  means  the  passage  of  fluids 
through  the  pores  of  a  membrane  under  pressure.  The  greater  the 
pressure  tbe  greater  the  amount  which  passes  through  the  membrane. 
€olloids  will  filter,  although  less  easily  than  crystalloids.  The  nature  of 
the  substance  to  be  filtered  and  the  nature  of  the  membrane  which  acts 
as  the  filter  materially  affect  the  activity  of  the  process.  No  doubt  both 
osmosis  and  filtration  go  on  together  in  the  process  of  absorption.  An 
excellent  example  of  filtration  or  transudation  occurs  in  the  pathological 
condition  known  as  drops}',  in  which  the  connective  tissues  become  in- 
filtrated with  serous  fluid.  The  fluid  passes  out  of  the  vein  when  the 
intra-venous  pressure  passes  a  certain  point,  the  fluid  is,  as  it  were, 
squeezed  through  the  walls  of  the  vessels  by  this  excess  of  pressure. 

Rapidity  of  Absorption. — -The  rapidity  with  which  matters  may 
be  absorbed  from  the  stomach,  probably  by  the  blood-vessels  chiefly,  and 
diffused  through  the  textures  of  the  body,  has  been  found  by  experiment. 
It  appears  that  lithium  chloride  may  be  diffused  into  all  the  vascular 
textures  of  the  body,  and  into  some  of  the  non-vascular,  as  the  cartilage 
of  the  hip-joint,  as  well  as  into  the  aqueous  humor  of  the  eye,  in  a  quar- 
ter of  an  hour  after  being  given  on  an  empty  stomach.  Into  the  outer 
part  of  the  crystalline  lens  it  may  pass  after  a  time,  varying  from  half 
an  hour  to  an  hour  and  a  half.  Lithium  carbonate,  when  taken  in  five 
or  ten-grain  doses  on  an  empty  stomach,  may  be  detected  in  the  urine  in 
5  or  10  minutes;  or,  if  the  stomach  be  full  at  the  time  of  taking  the  dose, 
in  20  minutes.  It  may  sometimes  be  detected  in  the  urine,  moreover, 
for  six,  seven,  or  eight  days. 

Some  experiments  on  the  absorption  of  various  mineral  and  vegetable 
poisons  have  brought  to  light  the  singular  fact  that,  in  some  cases,  ab- 
sorption takes  place  more  rapidly  from  the  rectum  than  from  the 
stomach.  Strychnia,  for  example,  when  in  solution,  produces  its  poi- 
sonous effects  much  more  speedily  when  introduced  into  the  rectum  than 
into  the  stomach.  When  introduced  in  the  solid  form,  however,  it  is 
absorbed  more  rapidly  from  the  stomach   than  from  the  rectum,  doubt- 


314  HANDBOOK    OF    PHYSIOLOGY. 

less  because  of  the  greater  solvent  property  of  the  secretion  of  the  former 
than  of  the  latter. 

With  regard  to  the  degree  of  absorption  by  living  blood-vessels,  much 
depends  on  the  facility  with  which  tbe  substance  to  be  absorbed  can 
penetrate  the  membrane  or  tissue  which  lies  between  it  and  the  blood- 
vessels. Thus,  absorption  will  hardly  take  place  through  the  epidermis, 
but  is  quick  when  the  epidermis  is  removed,  and  the  same  vessels  are 
covered  with  only  the  surface  of  the  cutis,  or  with  granulations.  In 
general,  the  absorption  through  membranes  is  in  an  inverse  proportion 
to  the  thickness  of  their  epithelia;  so  that  the  urinary  bladder  of  a  frog 
is  traversed  in  less  than  a  second;  and  the  absorption  of  poisons  by  the 
stomach  or  lungs  appears  sometimes  accomplished  in  an  immeasurably 
small  time. 

Conditions  for  Absorption. — 1.  The  substance  to  be  absorbed  must, 
as  a  general  rule,  he  in  the  liquid  or  gaseous  state,  or,  if  a  solid,  must  be 
soluble  in  the  fluids  with  ivhich  it  is  brought  into  contact.  Hence  the 
marks  of  tattooing,  and  the  discoloration  produced  by  silver  nitrate 
taken  internally,  remain.  Mercury  may  be  absorbed  even  in  the  metallic 
state;  and  in  that  state  may  pass  into  and  remain  in  the  blood-vessels, 
or  be  deposited  from  them;  and  such  substances  as  exceedingly  fiuely- 
divided  charcoal,  when  taken  into  the  alimentary  canal,  have  been  found 
in  the  mesenteric  veins;  the  insoluble  materials  of  ointments  may  also 
be  rubbed  into  the  blood-vessels;  but  there  are  no  facts  to  determine 
how  these  various  substances  effect  their  passage.  Oil,  minutely  divided, 
as  in  an  emulsion,  will  pass  slowly  into  blood-vessels,  as  it  will  through 
a  filter  moistened  with  water ;  and,  without  doubt,  fatty  matters  find 
their  way  into  the  blood-vessels  as  well  as  the  lymph-vessels  of  the  in- 
testinal canal,  although  the  latter  seem  to  be  specially  intended  for  their 
absorption. 

•  2.  The  less  dense  the  fluid  to  be  absorbed,  the  more  speedy,  as  a  gen- 
eral rule,  is  its  absorption  by  the  living  blood-vessels.  Hence  the  rapid 
absorption  of  water  from  the  stomach  ;  also  of  weak  saline  solutions ; 
but  with  strong  solutions,  there  appears  less  absorption  into,  than  effu- 
sion from,  the  blood-vessels. 

3.  The  absorption  is  the  less  rapid  the  fuller  and  tenser  the  blood- 
vessels are  ;  and  the  tension  may  be  so  great  as  to  hinder  altogether  the 
entrance  of  more  fluid.  Thus,  if  water  is  injected  into  a  dog's  veins  to 
repletion,  poison  is  absorbed  very  slowly  ;  but  when  the  tension  of  the 
vessels  is  diminished  by  bleeding,  the  poison  acts  quickly.  So,  when 
cupping-glasses  are  placed  over  a  poisoned  wound,  they  retard  the  ab- 
sorption of  the  poison  not  only  by  diminishing  the  velocity  of  the  circu- 
lation in  the  part,  but  by  filling  all  its  vessels  too  full  to  admit  more. 

4.  On  the  same  ground,  absorption  is  the  quicker  the  more  rapid  the 


ABSORPTION. 


315 


circulation  of  the  Mood;  not  because  the  fluid  to  be  absorbed  is  more 
quickly  imbibed  into  the  tissues,  or  mingled  with  the  blood,  but  because 
as  fast  as  it  enters  the  blood,  it  is  carried  away  from  the  part,  and  the 
blood  being  constantly  renewed,  is  constantly  as  fit  as  at  the  first  for  the 
reception  of  the  substance  to  be  absorbed. 


CHAPTER   IX. 

ANIMAL   HEAT. 

The  Average  Temperature  of  the  human  body  in  those  internal  parts 
-which  are  most  easily  accessible,  as  the  mouth  and  rectum,  is  from  98.5° 
to  99.5°  F.  (36.9°-37.4°  0.)-  In  different  parts  of  the  external  surface 
of  the  human  body  the  temperature  varies  only  to  the  extent  of  two  or 
three  degrees  (F.),  when  all  are  alike  protected  from  cooling  influences; 
and  the  difference  which  under  these  circumstances  exists,  depends 
chiefly  upon  the  different  degrees  of  blood-supply.  In  the  armpit — the 
most  convenient  situation,  under  ordinary  circumstances,  for  examina- 
tion by  the  thermometer — the  average  temperature  is  98.6°  F.  (36.9°  C). 
In  different  internal  parts,  the  variation  is  one  or  two  degrees  ;  those 
parts  and  organs  being  warmest  which  contain  most  blood,  and  in  which 
there  occurs  the  greatest  amount  of  chemical  change,  e.g.,  the  glands 
and  the  muscles  ;  and  the  temperature  is  highest,  of  course,  when  they 
are  most  actively  working  :  while  those  tissues  which,  subserving  only  a 
mechanical  function,  are  the  seat  of  least  active  circulation  and  chemical 
change,  are  the  coolest.  These  differences  of  temperature,  however,  are 
actually  but  slight,  on  account  of  the  provisions  which  exist  for  main- 
taining uniformity  of  temperature  in  different  parts. 

Circumstances  causing  Variations  in  Temperature. — The  chief 
circumstances  by  which  the  temperature  of  the  healthy  body  is  influ- 
enced are  the  following: — Age;  Sex;  Period  of  the  day;  Exercise; 
Climate  and  Season  ;  Food  and  Drink. 

Age. — The  average  temperature  of  the  new-born  child  is  only  about 
1°  F.  (.54°  C.)  above  that  of  the  adult ;  and  the  difference  becomes  still 
more  trifling  during  infancy  and  early  childhood.  The  temperature 
falls  to  the  extent  of  about  .2°-.  5°  F.  from  early  infancy  to  puberty,  and 
by  about  the  same  amount  from  puberty  to  fifty  or  sixty  years  of  age. 
In  old  age  the  temperature  again  rises,  and  approaches  that  of  infancy  ; 
but  although  this  is  the  case,  yet  the  power  of  resisting  cold  is  less  in 
them — exposure  to  a  low  temperature  causing  a  greater  reduction  of  heat 
than  in  young  persons. 

Sex. — The  average  temperature  of  the  female  is  very  slightly  higher 
than  that  of  the  male. 

Period  of  the  Day. — The  temperature  undergoes  a  gradual  alteration, 


ANIMAL    HEAT.  317" 

to  the  extent  of  about  1°  to  1.5°  F.  (.54-.8°  0.)  in  the  course  of  the  day 
and  night ;  the  minimum  being  at  night  or  in  the  early  morning,  the 
maximum  late  in  the  afternoon. 

Exercise. — Active  exercise  raises  the  temperature  of  the  body  from  1° 
to  2°  F.  (.54-1.08°  C).  This  maybe  partly  ascribed  to  generally  in- 
creased combustion  processes,  and  partly  to  the  fact  that  every  muscular 
contraction  is  attended  by  the  development  of  one  or  two  degrees  of  heat 
in  the  acting  muscle;  and  that  the  heat  is  increased  according  to  the 
number  and  rapidity  of  these  contractions,  and  is  quickly  diffused  by  the 
blood  circulating  from  the  heated  muscles.  Possibly,  also,  some  small 
amount  of  heat  may  be  generated  in  the  various  movements,  stretchings? 
and  recoilings  of  the  other  tissues,  as  the  arteries,  whose  elastic  walls, 
alternately  dilated  and  contracted,  may  give  out  some  heat,  just  as  caout- 
chouc alternately  stretched  and  recoiling  becomes  hot. 

Climate  and  Season.  —The  temperature  of  the  human  body  is  the 
same  in  temperate  and  tropical  climates  (Furnell).  In  summer  the 
temperature  of  the  body  is  a  little  higher  than  in  winter  ;  the  difference 
amounting  to  about  a  third  of  a  degree  F. 

Food  and  Dritih. — The  effect  of  a  meal  upon  the  temperature  of  a 
body  is  but  small.  A  very  slight  rise  usually  occurs.  Cold  alcoholic 
drinks  depress  the  temperature  somewhat  (.5°  to  1°  F.).  Warm  alco- 
holic drinks,  as  well  as  warm  tea  and  coffee,  raise  the  temperature  (about 
.5°F.). 

In  disease  the  temperature  of  the  body  deviates  from  the  normal  stand- 
ard to  a  greater  extent  than  would  be  anticipated  from  the  slight  effect 
of  external  conditions  during  health.  Thus,  in  some  diseases,  as  pneu- 
monia and  typhus,  it  occasionally  rises  as  high  as  106°  or  107°  F.  (41°- 
41.6°  C.)  ;  and  considerably  higher  temperatures  have  been  noted.  In 
Asiatic  cholera,  on  the  other  hand,  a  thermometer  placed  in  the  mouth 
may  sometimes  rise  only  to  77°  or  79°  F.  (25°-26.2  C). 

The  temperature  maintained  by  Mammalia  in  an  active  state  of  life, 
according  to  the  tables  of  Tiedemann  and  Eudolphi,  averages  101°  (38.3° 
(J.).  The  extremes  recorded  by  them  were  96°  and  106°,  the  former  in 
the  narwhal,  the  latter  in  a  bat  (Vespertilio  pipistrella).  In  Birds,  the 
average  is  as  high  as  107°  (41.2°  C.)  ;  the  highest  temperature,  111.25° 
(46.2°  C.)  ;  being  in  the  small  species,  the  linnets,  etc.  Among  Rep- 
tiles, while  the  medium  they  were  in  was  75°  (23.9°  C),  their  average 
temperature  was  82.5°  (31.2°  C).  As  a  general  rule,  their  temperature, 
though  it  falls  with  that  of  the  surrounding  medium,  is,  in  temperate 
media,  two  or  more  degrees  higher;  and  though  it  rises  also  with  that 
of  the  medium,  yet  at  very  high  degrees  it  ceases  to  do  so,  and  remains 
even  lower  than  that  of  the  medium.  Fish  and  invertebrata  present,  as 
a  general  rule,  the  same  temperature  as  the  medium  in  which  they  live, 
whether  that  be  high  or  low;  only  among  fish,  the  tunny  tribe,  with 
strong  hearts  and  red  meat-like  muscles,  and  more  blood  than  the  average 
fish  have,  are  generally  7°  (3.8°  C.)  warmer  than  the  water  around  them. 


318  HANDBOOK    OF  PHYSIOLOGY. 

The  difference,  therefore,  between  what  are  commonly  called  the 
warm  and  the  cold-blooded  animals  is  not  one  of  absolutely  higher  or 
lower  temperature  ;  for  the  animals  which  to  us  in  a  temperate  climate, 
feel  cold  (being  like  the  air  or  water,  colder  than  the  surface  of  our 
bodies),  would  in  an  external  temperature  of  100°  (37.8°  C.)  have  nearly 
the  same  temperature  and  feel  hot  to  us.  The  real  difference  is  that  what 
we  call  warm-blooded  animals  (Birds  and  Mammalia),  have  a  certain 
"permanent  heat  in  all  atmospheres,"  while  the  temperature  of  the 
others,  which  we  call  cold-blooded,  is  ' '  variable  with  every  atmosphere." 
(Hunter.) 

The  power  of  maintaining  a  uniform  temperature,  which  Mammalia 
and  Birds  possess,  is  combined  with  the  want  of  power  to  endure  such 
changes  of  body  temperature  as  are  harmless  to  the  other  classes;  and 
when  their  power  of  resisting  change  of  temperature  ceases,  they  suffer 
serious  disturbance  or  die. 


Sources  and  Mode  of  Production  of  Heat  in  the  Body. — The 

heat  which  is  produced  in  the  body  arises  from  combustion,  and  is  due 
to  the  fact  that  the  oxygen  of  the  atmosphere  taken  into  the  system  is 
ultimately  combined  with  carbon  and  hydrogen,  and  discharged  from 
the  body  as  carbonic  acid  and  water.  Any  changes,  indeed,  which  occur 
in  the  protoplasm  of  the  tissues,  resulting  in  an  exhibition  of  their  func- 
tion, are  attended  by  the  evolution  of  heat  and  the  formation  of  carbonic 
acid  and  water.  The  more  active  the  changes,  the  greater  is  the  heat 
produced  and  the  greater  is  the  amount  of  the  carbonic  acid  and  water 
formed.  But  in  order  that  the  protoplasm  may  perform  its  function,  the 
waste  of  its  own  tissue  (destructive  metabolism)  must  be  repaired  by  the 
due  supply  of  food  material  and  therefore  for  the  production  of  heat 
food  is  necessary.  In  the  tissues,  therefore,  two  processes  are  continu- 
ally going  on:  the  building  up  of  the  protoplasm  from  the  food  (con- 
structive metabolism),  which  is  not  accompanied  by  the  evolution  of 
heat  but  possibly  by  the  reverse,  and  the  oxidation  of  the  protoplastic 
materials,  resulting  in  the  production  of  energy,  by  which  heat  is  pro- 
duced and  carbonic  acid  and  water  are  evolved.  Some  heat  also  is 
generated  in  the  combination  of  sulphur  and  phosphorus  with  oxygen, 
but  the  amount  thus  produced  is  but  small. 

It  is  not  necessary  to  assume  that  the  combustion  processes,  which 
ultimately  issue  in  the  production  of  carbonic  acid  and  water,  are  as 
simple  as  the  bare  statement  of  the  fact  might  seem  to  indicate.  But 
complicated  as  the  various  stages  may  be,  the  ultimate  result  is  as  simple 
as  in  ordinary  combustion  outside  of  the  body,  and  the  products  are  the 
same.  The  same  amount  of  heat  will  be  evolved  in  the  union  of  any 
given  quantities  of  carbon  and  oxygen,  and  of  hydrogen  and  oxygen, 
whether  the  combination  be  rapid  and  direct,  as  in  ordinary  combustion, 
or  slow  and  almost  imperceptible,  as  in  the  changes  which  occur  in  the 
living  body.     And  since  the  heat  thus  arising  will  be  distributed  wherever 


ANIMAL    HEAT.  319 

the  blood  is  canned,  every  part  of  the  body  will  be  heated  equally,  or 
nearly  so. 

This  theory,  that  the  maintenance  of  the  temperature  of  the  living 
body  depends  on  continual  chemical  change,  chiefly  by  oxidation  of  com- 
bustible materials  existing  in  the  tissues,  has  long  been  established  by 
the  demonstration  that  the  quantity  of  carbon  and  hydrogen  which,  in  a 
given  time,  unites  in  the  body  with  oxygen,  is  sufficient  to  account  for 
the  amount  of  heat  generated  in  the  animal  within  the  same  period:  an 
amount  capable  of  maintaining  the  temperature  of  the  body  at  from 
98°-100°  F.  (36.8°-37.8°  C),  notwithstanding  a  large  loss  by  radiation 
and  evaporation. 

It  should  be  remembered  that  some  heat  may  be  introduced  into  the 
body  by  means  of  warm  drinks  and  foods,  and,  again,  that  it  is  possible 
for  the  preliminary  digestive  changes  to  be  accompanied  by  the  evolution 
of  heat. 

Chief  Heat-producing  Tissues. — The  chemical  changes  which 
produce  the  body-heat  appear  to  be  especially  active  in  certain  tissues: — 
(1)  In  the  Muscles,  which  form  so  large  a  part  of  the  organism.  The 
fact  that  the  manifestation  of  muscular  energy  is  always  attended  by  the 
evolution  of  heat  and  the  production  of  carbonic  acid  has  been  demon- 
strated by  actual  experiment;  and  when  not  actually  in  a  condition  of 
active  contraction,  a  metabolism,  not  so  active  but  still  actual,  goes  on, 
which  is  accompanied  by  the  manifestation  of  heat.  The  total  amount 
set  free  by  the  muscles,  therefore,  must  be  very  great;  and  it  has  been 
calculated  in  a  way  which  wrill  be  referred  to  later  on,  that  even  neglect- 
ing the  heat  produced  by  the  quiet  metabolism  of  muscular  tissue, 
the  amount  of  heat  generated  by  muscular  activity  supplies  the  principal 
part  of  the  total  heat  produced  within  the  body.  (2)  In  the  Secreting 
glands,  and  principally  in  the  liver  as  being  the  largest  and  most  active. 
It  has  been  found  by  experiment  that  the  blood  leaving  the  glands  is 
considerably  warmer  than  that  entering  them.  The  metabolism  in  the 
glands  is  very  active  and,  as  we  have  seen,  the  more  active  the  metabo- 
lism the  greater  the  heat  produced.  (3)  In  the  Brain;  the  venous 
blood  having  a  higher  temperature  than  the  arterial.  It  must  be  re- 
membered, however,  that  although  the  organs  above  mentioned  are  the 
chief  heat-producing  parts  of  the  body,  all  living  tissues  contribute  their 
quota,  and  this  in  direct  proportion  to  their  activity.  The  blood  itself 
is  also  the  seat  of  metabolism,  and,  therefore,  of  the  production  of  heat: 
but  the  share  which  it  takes  in  this  respect,  apart  from  the  tissues  in 
which  it  circulates,  is  very  inconsiderable. 

Regulation  of  the  Temperature  of  the  Human  Body. 
The  average  temperature  of  the  body  is  maintained  under  different 
conditions  of  external  circumstances  by  mechanisms  which  permit  of  (1) 


320  HANDBOOK    OF   PHYSIOLOGY. 

variation  in  the  amount  of  heat  got  rid  of,  and  (2)  variations  in  the 
amout  of  heat  produced  or  introduced  into  the  body.  In  healthy  warm- 
blooded animals  the  loss  and  gain  of  heat  are  so  nearly  balanced  one  by 
the  other  that,  under  all  ordinary  circumstances,  an  uniform  tempera- 
ture, within  two  or  three  degrees,  is  preserved. 

I.  Methods  of  Variation  in  the  amount  of  Heat  got  rid  of. 
— The  loss  of  heat  from  the  human  body  is  principally  regulated  by  the 
amount  lost  by  radiation  and  conduction  from  its  surface,  and  by  means 
of  the  constant  evaporation  of  water  from  the  same  part,  and  (2)  to  a 
much  less  degree  from  the  air-passages;  in  each  act  of  respiration,  heat 
is  lost  to  a  greater  or  less  extent  according  to  the  temperature  of  the  at- 
mosphere; unless  indeed  the  temperature  of  the  surrounding  air  exceed 
that  of  the  blood.  We  must  remember  too  that  all  food  and  drink 
which  enter  the  body  at  a  lower  temperature  than  itself  abstract  a  small 
measure  of  heat  ;  while  the  urine  and  fasces  which  leave  the  body  at 
about  its  own  temperature  are  also  means  by  which  a  small  amount  is 
lost. 

(a.)  Loss  of  Heat  from  the  Surf  ace  of  the  Body:  the  Shin. — By  far 
the  most  important  loss  of  heat  from  the  body — probably  70  or  80  per 
cent  of  the  whole  amount,  is  that  which  takes  place  by  radiation,  con- 
duction, and  evaporation  from  the  skin.  The  means  by  which  the  skin 
is  able  to  act  as  one  of  the  most  important  organs  for  regulating  the 
temperature  of  the  blood  are — (1),  that  it  offers  a  large  surface  for  radi- 
ation, conduction,  and  evaporation  ;  (2),  that  it  contains  large  amount 
of  blood  ;  (3),  that  the  quantity  of  blood  contained  in  it  is  the  greater 
under  those  circumstances  which  demand  a  loss  of  heat  from  the  body, 
and  vice  versa.  For  the  circumstance  which  directly  determines  the 
quantity  of  blood  in  the  skin,  is  that  which  governs  the  supply  of  blood 
to  all  the  tissue  and  organs  of  the  body,  namely,  the  power  of  the  vaso- 
motor nerves  to  cause  a  greater  or  less  tension  of  the  muscular  element 
in  the  walls  of  the  arteries,  and,  in  correspondence  with  this„.  a  lessen- 
ing or  increase  of  the  calibre  of  the  vessel,  accompanied  by  a  less  or 
greater  current  of  blood.  A  warm  or  hot  atmosphere  so  acts  on  the 
nerve-fibres  of  the  skin,  as  to  lead  them  to  cause  in  turn  a  relaxation  of 
the  mucular  fibre  of  the  blood-vessels;  and,  as  a  result,  the  skin  becomes 
full-blooded,  hot,  and  sweating;  and  much  heat  is  lost.  With  a  low 
temperature,  on  the  other  hand,  the  blood-vessels  shrink,  and  in  accord- 
ance with  the  consequently  diminished  blood-supply,  the  skin  becomes 
pale,  and  cold,  and  dry;  and  no  doubt  a  similar  effect  may  be  produced 
through  the  vaso-motor  centre  in  the  medulla  and  spinal  cord.  Thus, 
by  means  of  a  self- regulating  apparatus,  the  skin  becomes  the  most  im- 
portant of  the  means  by  which  the  temperature  of  the  body  is  regulated. 

In  connection  with  loss  of  heat  by  the  skin,  reference  has  been  made 
to  that  which  occurs  both  by  radiation  and  conduction,  and  by  evapora- 


ANIMAL    HEAT.  321 

tion  ;  and  the  subject  of  animal  heat  has  been  considered  almost  solely 
with  regard  to  the  ordinary  case  of  man  living  in  a  medium  colder  than 
his  body,  and  therefore  losing  heat  in  all  the  ways  mentioned.  The  im- 
portance of  the  means  however,  adopted,  so  to  speak,  by  the  skin  for  reg- 
ulating the  temperature  of  the  body,  will  depend  on  the  conditions  by 
which  it  is  surrounded;  an  inverse  proportion  existing  in  most  cases  be- 
tween the  loss  by  radiation  and  conduction  on  the  one  hand,  and  by 
evaporation  on  the  other.  Indeed,  the  small  loss  of  heat  by  evaporation 
in  cold  climates  may  go  far  to  compensate  for  the  greater  loss  by  radia- 
tion; as,  on  the  other  hand,  the  great  amount  of  fluid  evaporated  in 
hot  air  may  remove  nearly  as  much  heat  as  is  commonly  lost  by  both 
radiation  and  evaporation  in  ordinary  temperatures;  and  thus,  it  is  pos- 
sible that  the  quantities  of  heat  required  for  the  maintenance  of  an  uni- 
form proper  temperature  in  various  climates  and  seasons  are  not  so 
different  as  they,  at  first  thought,  seem. 

Many  examples  may  be  given  of  the  power  which  the  body  possesses 
of  resisting  the  effects  of  a  high  temperature,  in  virtue  of  evaporation 
from  the  skin.  Blagden  and  others  supported  a  temperature  varying 
between  198°-211°  F.  (92°-100°  C.)  in  dry  air  for  several  minutes, 
and  in  a  subsequent  experiment  he  remained  eight  minutes  in  a  temper- 
ature of  260°  K.  (126.5°  C.)  "The  workmen  of  Sir  F.  Chantrey  were 
accustomed  to  enter  a  furnace,  in  which  his  moulds  were  dried,  whilst 
the  floor  was  red-hot,  and  a  thermometer  in  the  air  stood  at  350°  F. 
(177.8°  C),  and  Chabert,  the  fire-king,  was  in  the  habit  of  entering  an 
oven,  the  temperature  of  which  was  from  400°  to  600°  F.  (205°-315° 
C.)."     (Carpenter.) 

But  such  heats  are  not  tolerable  when  the  air  is  moist  as  well  as  hot, 
so  as  to  prevent  evaporation  from  the  body.  C.  James  states,  that  in 
the  vapor  baths  of  Nero  he  was  almost  suffocated  in  a  temperature  of 
112°  F.  (44.5°  C),  while  in  the  caves  of  Testaccio,  in  which  the  air  is 
dry,  he  was  but  little  incommoded  by  a  temperature  of  176°  F.  (80°  C). 
In  the  former,  evaporation  from  the  skin  was  impossible;  in  the  latter 
it  was  abundant,  and  the  layer  of  vapor  which  would  rise  from  all  the 
surface  of  the  body  would,  by  its  very  slowly  conducting  power,  defend 
it  for  a  time  from  the  full  action  of  the  external  heat. 

(The  glandular  apparatus,  by  which  secretion  of  fluid  from  the  skin 
is  effected,  will  be  considered  in  the  Section  on  the  Skin.) 

The  ways  by  which  the  skin  may  be  rendered  more  efficient  as  a  cool- 
ing apparatus  by  exposure,  by  baths,  and  by  other  means  which  man  in- 
stinctively adopts  for  lowering  his  temperature  when  necessary,  are  too 
well  known  to  need  more  than  to  be  mentioned. 

Although  under  any  ordinary  circumstances,  the  external  applica- 
tion of  cold  only  temporarily  depresses  the  temperature  to  a  slight  ex- 
tent, it  is  otherwise  in  cases  of  high  temperature  in  fever.  In  these 
cases  a  tepid  bath  may  reduce  the  temperature  several  degrees,  and  the 
effect  so  produced  lasts  in  some  cases  for  many  hours. 
21 


322  HANDBOOK   OF    PHYSIOLOGY. 

(b.)  Loss  of  Heat  from  the  Lungs. — As  a  means  for  lowering  the  tem- 
perature, the  lungs  and  air-passages  are  very  inferior  to  the  skin  ;  al- 
though, by  giving  heat  to  the  air  we  breathe,  they  stand  next  to  the 
skin  in  importance.  As  a  regulating  power,  the  inferiority  is  still  more 
marked.  The  air  which  is  expelled  from  the  lungs  leaves  the  body  at 
about  the  temperature  of  the  blood,  and  is  always  saturated  with  moist- 
ure. No  inverse  proportion,  therefore,  exists,  as  in  the  case  of  the  skin, 
between  the  loss  of  heat  by  radiation  and  conduction  on  the  one  hand, 
and  by  evaporation  on  the  other.  The  colder  the  air,  for  example,  the 
greater  will  be  the  loss  in  all  ways.  Neither  is  the  quantity  of  blood 
which  is  exposed  to  the  cooling  influence  of  the  air  diminished  or  in- 
creased, so  far  as  is  known,  in  accordance  with  any  need  in  relation  to 
temperature.  It  is  true  that  by  varying  the  number  and  depth  of  the 
respirations,  the  quantity  of  heat  given  off  by  the  lungs  may  be  made, 
to  some  extent,  to  vary  also.  But  the  respiratory  passages,  while  they 
must  be  considered  important  means  by  which  heat  is  lost,  are  altogether 
subordinate,  in  the  power  of  regulating  the  temperature,  to  the  skin. 

(c.)  By  Clothing. — The  influence  of  external  coverings  for  the  body 
must  not  be  unnoticed.  In  warm-blooded  animals,  they  are  always 
adapted,  among  other  purposes,  to  the  maintenance  of  uniform  temper- 
ature ;  and  man  adapts  for  himself  such  as  are,  for  the  same  purpose, 
fitted  to  the  various  climates  to  which  he  is  exposed.  By  their  means, 
and  by  his  command  over  food  and  fire,  he  maintains  his  temperature  on 
all  accessible  parts  of  the  surface  of  the  earth. 

II.  Methods  of  Variation  in  the  Amount  of  Heat  Produced. 
— It  may  seem  to  have  been  assumed,  in  the  foregoing  pages,  that  the 
only  regulating  apparatus  for  temperature  required  by  the  human  body 
is  one  that  shall,  more  or  less,  produce  a  cooling  effect ;  and  as  if  the 
amount  of  heat  produced  were  always,  therefore,  in  excess  of  that  which 
is  required.  Such  an  assumption  would  be  incorrect.  "We  have  the 
power  of  regulating  the  production  of  heat,  as  well  as  its  loss. 

(a.)  By  Regulating  the  Quantity  and  Quality  of  the  Food  taken. — 
In  food  we  have  a  means  for  elevating  our  temperature.  It  is  the  fuel, 
indeed,  on  which  animal  heat  ultimately  depends  altogether.  Thus, 
when  more  heat  is  wanted,  we  instinctively  take  more  food,  and  take 
such  kinds  of  it  as  are  good  for  combustion ;  while  every-day  experience 
shows  the  different  power  of  resisting  cold  possessed,  respectively,  by  the 
well-fed  and  by  the  starved.  In  northern  regions,  again,  and  in  the 
colder  seasons  of  more  southern  climes,  the  quantity  of  food  consumed 
is  (speaking  very  generally)  greater  than  that  consumed  by  the  same  men 
or  animals  in  opposite  conditions  of  climate  and  season.  And  the  food 
which  appears  naturally  adapted  to  the  inhabitants  of  the  coldest  cli- 
mates, such  as  the  several  fatty  and  oily  substances,  abounds  in  carbon 
and  hydrogen,  and  is  fitted  to  combine  ultimately  with  the  large  quanti- 


ANIMAL    HEAT.  32-3 

ties  of  oxygen  which,  breathing  cold  dense  air,  the}'  absorb  from  their 
lungs. 

(b.)  By  Exercise. — In  exercise,  we  have  an  important  means  of  rais- 
ing the  temperature  of  our  bodies. 

(c.)  By  Influence  of  the  Nervous  System. — The  influence  of  the 
nervous  system  in  modifying  the  production  of  heat  must  be  very 
important,  as  upon  nervous  influence  depends  the  amount  of  the  metabo- 
lism of  the  tissues.  The  experiments  and  observations  which  best  illus- 
trate it  are  those  showing,  first,  that  when  the  supply  of  nervous  influ- 
ence to  a  part  is  cut  off,  the  temperature  of  that  part  after  a  time  falls 
below  its  ordinary  degree  ;  and,  secondly,  that  when  death  is  caused  by 
severe  injury  to,  or  removal  of,  the  nervous  centres,  the  temperature  of 
the  body  rapidly  falls,  even  though  artificial  respiration  be  performed, 
the  circulation  maintained  and  to  all  appearance  the  ordinary  chemical 
changes  of  the  body  be  completely  effected.  It  has  been  rej^eatedly  no- 
ticed, that  after  division  of  the  nerves  of  a  limb  its  temperature  ulti- 
mately falls  ;  and  this  diminution  of  heat  has  been  remarked  still  more 
plainly  in  limbs  deprived  of  nervous  influence  by  paralysis. 

With  equal  certainty,  though  less  definitely,  the  influence  of  the 
nervous  system  on  the  production  of  heat,  is  shown  in  the  rapid  and 
momentary  increase  of  temperature,  sometimes  general,  at  other  times 
quite  local,  which  is  observed  in  states  of  nervous  excitement;  in  the 
general  increase  of  warmth  of  the  body,  sometimes  amounting  to  perspi- 
ration, which  is  excited  by  passions  of  the  mind;  in  the  sudden  rush  of 
heat  to  the  face,  which  is  not  a  mere  sensation;  and  in  the  equally  rapid 
diminution  of  temperature  in  the  depressing  passions.  But  none  of 
these  instances  suffice  to  prove  that  heat  is  generated  by  mere  nervous 
action,  independent  of  any  chemical  change;  all  are  explicable,  on  the 
supposition  that  the  nervous  system  alters,  by  it  power  of  controlling  the 
calibre  of  the  blood-vessels  (p.  14 1),  the  quantity  of  blood  supplied  to  a 
part;  while  any  influence  which  the  nervous  system  may  have  in  the 
production  of  heat,  apart  from  this  influence  on  the  blood-vessels,  is  an 
indirect  one,  and  is  derived  from  its  power  of  causing  such  nutritive 
change  in  the  tissues  as  may,  by  involving  the  necessity  of  chemical 
action,  involve  the  production  of  heat.  The  existence  of  nerve-centres 
and  nerves  which  regulate  animal  heat  (thermogenic)  otherwise  than  by 
their  influence  in  trophic  (nutritive)  or  vaso-motor  changes,  although  by 
many  considered  probable,  is  not  yet  proven. 

Inhibitory  heat-centre. — Whether  a  centre  exists  which  regulates  the 
production  of  heat  in  warm-blooded  animals,  is  still  undecided.  Ex- 
periments have  shown  that  exposure  to  cold  at  once  increases  the  oxygen 
taken  in,  and  the  carbonic  acid  given  out,  indicating  an  increase  in  the 
activity  of  the  metabolism  of  the  tissues,  but  that  in  animals  poisoned 
by  urari,  exposure   to   cold  diminishes  both  the  metabolism  and  the 


324  HANDBOOK    OF    PHYSIOLOGY. 

temperature,  and  warm-blooded  animals  then  react  to  variations  of  the 
external  temperature  just  in  the  same  way  as  cold-blooded.  These,  ex- 
periments seem  to  suggest  that  there  is  a  centre,  to  which,  under  nor- 
mal circumstances,  the  impression  of  cold  is  conveyed,  and  from  which 
by  efferent  nerves  impulses  pass  to  the  muscles,  whereby  an  increased 
metabolism  is  induced,  and  so  an  increased  amount  of  heat  is  generated. 
The  centre  is  probably  situated  above  the  medulla.  Thus  in  urarized 
animals,  as  the  nerves  to  the  muscles,  the  metabolism  of  which  is  so  im- 
portant in  the  production  of  heat,  are  paralyzed,  efferent  impulses  from 
the  ceutre  cannot  induce  the  necessary  metabolism  for  the  production 
of  heat,  even  though  afferent  impulses  from  the  skin,  stimulated  by  the 
alteration  of  temperature,  have  conveyed  to  it  the  necessity  of  altering 
the  amount  of  heat  to  be  produced.  The  same  effect  is  produced  when 
the  medulla  is  cut. 

Influence  of  Extreme  Heat  and  Cold. — In  connection  with  the 
regulation  of  animal  temperature,  and  its  maintenance  in  health  at  the 
normal  height,  may  be  noted  the  result  of  circumstances  too  powerful, 
either  in  raising  or  lowering  the  heat  of  the  body,  to  be  controlled  by  the 
proper  regulating  apparatus.  Walther  found  that  rabbits  and  dogs  kept 
exposed  to  a  hot  sun,  reached  a  temperature  of  114. 8°  F.,  and  then  died. 
Cases  of  sunstroke  furnish  us  with  several  examples  in  the  case  of  man; 
for  it  would  seem  that  here  death  ensues  chiefly  or  solely  from  elevation 
of  the  temperature.  In  many  febrile  diseases  the  immediate  cause  of 
death  appears  to  be  the  elevation  of  the  temperature  to  a  point  incon- 
sistent with  the  continuance  of  life. 

The  effect  of  mere  loss  of  bodily  temperature  in  man  is  less  well 
known  than  the  effect  of  heat.  From  experiments  by  Walther,  it  ap- 
pears that  rabbits  can  be  cooled  down  to  48°  F.  (8.9°  C),  before  they 
die,  if  artificial  respiration  be  kept  up.  Cooled  down  to  64°  F.  (17.8° 
C),  they  cannot  recover  unless  external  warmth  be  applied  together 
with  the  employment  of  artificial  respiration.  Eabbits  not  cooled  below 
77°  F.  (25°  C.)  recover  by  external  warmth  alone. 


CHAPTER   X. 

SECRETION. 

Secretion  is  the  process  by  which  materials  are  separated  from  the 
blood  by  the  cells  of  secreting  glands  and  membranes,  and  are  either 
elaborated  for  the  purpose  of  serving  some  ulterior  office  in  the  economy, 
or  are  discharged  from  the  body  as  useless  or  injurious.  In  the  former 
case,  the  separated  materials  are  termed  secretions;  in  the  latter,  they 
are  termed  excretions. 

Most  of  the  secretions  consist  of  substances  which,  probably,  do  not 
pre-exist  in  the  same  form  in  the  blood,  but  require  special  cells  and  a 
process  of  elaboration  for  their  formation,  e.  g.,  the  liver  cells  for  the 
formation  of  bile,  the  mammary  gland-cells  for  the  formation  of  milk. 
The  excretions,  on  the  other  hand,  commonly  or  chiefly  consist  of  sub- 
stances which  exist  ready-formed  in  the  blood,  and  are  merely  abstracted 
therefrom.  If  from  any  cause,  such  as  extensive  disease  or  extirpation 
of  an  excretory  organ,  the  separation  of  an  excretion  is  prevented,  and 
an  accumulation  of  it  in  the  blood  ensues,  it  frequently  escapes  through 
other  organs,  and  may  be  detected  in  various  fluids  of  the  body.  But 
this  is  never  the  case  with  secretions;  at  least  with  those  that  are  most 
elaborated  ;  for  after  the  removal  of  the  special  organ  by  which  each  of 
them  is  elaborated,  the  secretion  is  no  longer  formed.  Cases  sometimes 
occur  in  which  the  secretion  continues  to  be  formed  by  the  natural  or- 
gan, but  not  being  able  to  escape  towards  the  exterior,  on  account  of 
some  obstruction,  is  re-absorbed  into  the  blood,  and  afterwards  discharged 
from  it  by  exudation  in  other  ways;  but  these  are  not  instances  of  true 
vicarious  secretion,  and  must  not  be  thus  regarded. 

These  circumstances,  and  their  final  destination,  are,  however,  the 
only  particulars  in  which  secretions  and  excretions  can  be  distinguished; 
for,  in  general,  the  structure  of  the  parts  engaged  in  eliminating  excre- 
tions is  as  complex  as  that  of  the  parts  concerned  in  the  formation  of 
secretions.  And  since  the  differences  of  the  two  processes  of  separation, 
corresponding  with  those  in  the  several  purposes  and  destinations  of  the 
fluids,  are  not  yet  ascertained,  it  will  be  sufficient  to  speak  in  general 
terms  of  the  process  of  separation  or  secretion. 

Every  secreting  apparatus  possesses,  as  essential  parts  of  its  structure, 
a  simple  and  almost  textureless  membrane,  named   the  primary  or  base- 


326  HANDBOOK   OF    PHYSIOLOGY. 

merit-membrane;  certain  cells;  and  blood-vessels.  These  three  structural 
elements  are  arranged  together  in  various  ways;  but  all  the  varieties  may 
be  classed  under  one  or  other  of  two  principal  divisions,  namely,  mem- 
branes and  glands. 

Organs  and  Tissues  of  Secretion. 

The  principal  secreting  membranes  are  (1)  the  Serous  and  Synovial 
membranes;  (2)  the  Mucous  membranes;  (3)  the  Mammary  gland;  (4) 
the  Lachrymal  gland;  and  (5)  the  Skin. 

(1)  Serous  Membranes. 

The  serous  membranes  are  especially  distinguished  by  the  characters 
of  the  endothelium  covering  their  free  surface:  it  always  consists  of  a 
single  layer  of  polygonal  cells.  The  ground  substance  of  most  serous 
membranes  consists  of  connective-tissue  corpuscles  of  various  forms  lying 
in  the  branching  spaces  which  constitute  the  "  lymph  canalicular  sys- 
tem "  (p.  299),  and  interwoven  with  bundles  of  white  fibrous  tissue,  and 
numerous  delicate  elastic  fibrillar,  together  with  blood-vessels,  nerves,  and 
lymphatics.  In  relation  to  the  process  of  secretion,  the  layer  of  connec- 
tive tissue  serves  as  a  ground-work  for  the  ramification  of  blood-vessels, 
lymphatics,  and  nerves.  But  in  its  usual  form  it  is  absent  in  some  in- 
stances, as  in  the  arachnoid  covering  the  dura  mater,  and  in  the  interior 
of  the  ventricles  of  the  brain.  The  primary  membrane  and  epithelium 
are  always  present,  and  are  concerned  in  the  formation  of  the  fluid  by 
which  the  free  surface  of  the  membrane  is  moistened. 

Serous  membranes  are  of  two  principal  kinds:  1st.  Those  which  line 
visceral  cavities — the  arachnoid,  pericardium,  pleural,  peritoneum ,  and 
tunicce  vaginales.  2d.  The  synovial  membranes  lining  the  joints,  and 
the  sheaths  of  tendons  and  ligaments,  with  which,  also,  are  usually  in- 
cluded the  synovial  bursa},  or  bursa  mucosa},  whether  these  be  subcuta- 
neous, or  situated  beneath  tendons  and  glide  over  bones. 

The  serous  membranes  form  closed  sacs,  and  exist  wherever  the  free 
surfaces  of  viscera  come  into  contact  with  each  other  or  lie  in  cavities 
unattached  to  surrounding  parts.  The  viscera  invested  by  a  serous 
membrane  are,  as  it  were,  pressed  into  the  shut  sac  which  it  forms, 
carrying  before  them  a  portion  of  the  membrane,  which  serves  as  their 
investment.  To  the  law  that  serous  membranes  form  shut  sacs,  there  is, 
in  the  human  subject,  one  exception,  viz.:  the  opening  of  the  Fallopian 
tubes  into  the  abdominal  cavity — an  arrangement  which  exists  in  man 
and  all  Vertebrata,  with  the  exception  of  a  few  fishes. 

Functions. — The  principal  purpose  of  the  serous  and  synovial  mem- 
branes is  to  furnish  a  smooth,  moist  surface,  to  facilitate  the  movements 
of  the  invested  organ,  and  to  prevent  the  injurious  effects  of  friction.. 


SECKKTION. 


?2T 


This  purpose  is  especially  manifested  in  joints,  in  which  free  and  exten- 
sive movements  take  place;  and  in  the  stomach  and  intestines,  which, 
from  the  varying  quantity  and  movements  of  their  contents,  are  in  al- 
most constant  motion  upon  one  another  and  the  walls  of  the  abdomen. 

Fluid.  —  The  fluid  secreted  from  the  free  surface  of  the  serous  mem- 
branes is,  in  health,  rarely  more  than  sufficient  to  insure  the  maintenance 
of  their  moisture.  The  opposed  surfaces  of  each  serous  sac  are  at  every 
point  in  contact  with  each  other.  After  death,  a  larger  quantity  of  fluid 
is  usually  found  in  each  serous  sac;  but  this,  if  not  the  product  of  mani- 
fest disease,  is  probably  such  as  has  transuded  after  death,  or  in  the  last 
hours  of  life.  An  excess  of  such  fluid  in  any  of  the  serous  sacs  consti- 
tutes dropsy  of  the  sac. 

The  fluid  naturally  secreted  by  the  serous  membranes  appears  to  be 


Fig.  226.— Section  of  synovial  membrane,  a,  endothelial  covering  of  the  elevations  of  the  mem- 
rane;  b,  subserous  tissue  containing  fat  and  blood-vessels;  c,  ligament  covered  by  the  synovial 
membrane.    (Cadiat.) 

identical,  in  general  and  chemical  characters,  with  very  dilute  liquor 
sanguinis.  It  is  of  a  pale  yellow  or  straw  color,  slightly  viscid,  alkaline, 
and  on  account  of  the  presence  of  albumen,  coaguable  by  heat.  This 
similarity  of  the  serous  fluid  to  the  liquid  part  of  blood,  and  to  the 
fluid  with  which  most  animal  tissues  are  moistened,  renders  it  probable 
that  it  is,  in  great  measure,  separated  by  simple  transudation,  through 
the  walls  of  the  blood-vessels.  The  probability  is  increased  by  the  fact 
that,  in  jaundice,  the  fluid  in  the  serous  sacs  is,  equally  with  the  serum 
of  the  blood,  colored  with  the  bile.  But  there  is  reason  for  supposing 
that  the  fluid  of  the  cerebral  ventricles  and  of  the  arachnoid  sac  are  ex- 
ceptions to  this  rule;  for  they  differ  from  the  fluids  of  the  other  serous 


328  HANDBOOK    OF    PHYSIOLOGY. 

sacs  not  only  in  being  pellucid,  colorless,  and  of  much  less  specific 
gravity,  but  in  that  they  seldom  receive  the  tinge  of  bile  when  pres- 
ent in  the  blood,  and  are  not  colored  by  madder,  or  other  similar  sub- 
stances introduced  abundantly  into  the  blood. 

It  is  also  probable  that  the  formation  of  synovial  fluid  is  a  process  of 
more  genuine  and  elaborate  secretion,  by  means  of  the  epithelial  cells  on 
the  surface  of  the  membrane,  and  especially  of  those  which  are  accumu- 
lated on  the  edges  and  processes  of  the  synovial  fringes;  for,  in  its  pecu- 
liar density,  viscidity,  and  abundance  of  albumen,  synovia  differs  alike 
from  the  serum  of  blood  and  from  the  fluid  of  any  of  the  serous  cavities. 

(2)  Mucous  Membranes. 

The  mucous  membranes  line  all  those  passages  by  which  internal 
parts  communicate  with  the  exterior,  and  by  which  either  matters  are 
eliminated  from  the  body  or  foreign  substances  taken  into  it.  They  are 
soft  and  velvety,  and  extremely  vascular.  The  external  surfaces  of 
mucous  membranes  are  attached  to  various  other  tissues;  in  the  tongue, 
for  example,  to  muscle;  on  cartilaginous  parts,  to  perichondrium;  in  the 
cells  of  the  ethmoid  bone,  in  the  frontal  and  sphenoidal  sinuses,  as  well 
in  the  tympanum,  to  periosteum;  in  the  intestinal  canal,  it  is  connected 
with  a  firm  submucous  membrane,  which  on  its  exterior  gives  attach- 
ment to  the  fibres  of  the  muscular  coat.  The  mucous  membranes  line 
certain  principal  tracts — Grastro-Pulmonary  and  Genito-Urinary;  the 
former  being  subdivided  into  the  Digestive  and  Eespiratory  tracts. 

1.  The  Digestive  tract  commences  in  the  cavity  of  the  mouth,  from 
which  prolongations  pass  into  the  ducts  of  the  salivary  glands.  From 
the  mouth  it  passes  through  the  fauces,  pharynx,  and  oesophagus,  to  the 
stomach,  and  is  thence  continued  along  the  whole  tract  of  the  intestinal 
canal  to  the  termination  of  the  rectum,  being  in  its  course  arranged  in 
the  various  folds  and  depressions  already  described,  and  prolonged  into 
the  ducts  of  the  intestinal  glands,  the  pancreas  and  liver,  and  into  the 
gall-bladder. 

2.  The  Respiratory  tract  includes  the  mucous  membrane  lining  the 
cavity  of  the  nose,  and  the  various  sinuses  communicating  with  it,  the 
lachrymal  canal  and  sac,  the  conjunctiva  of  the  eye  and  eyelids,  and  the 
prolongation  which  passes  along  the  Eustachian  tubes  and  lines  the 
tympanum  and  the  inner  surface  of  the  membrana  tympani.  Crossing 
the  pharynx,  and  lining  that  part  of  it  which  is  above  the  soft  palate, 
the  respiratory  tract  leads  into  the  glottis,  whence  it  is  continued, 
through  the  larynx  and  trachea,  to  the  bronchi  and  their  divisions, 
which  it  lines  as  far  as  the  branches  of  about  -gL  of  an  inch  in  diameter, 
and  continuous  with  it  is  a  layer  of  delicate  epithelial  membrane  which 
extends  into  the  pulmonary  cells. 


8ECRETI0N.  329 

3.  The  Genii o-uririary  tract,  which  lines  the  whole  of  the  urinary 
passages,  from  their  external  orifice  to  the  termination  of  the  tubuli 
uriniferi  of  the  kidneys,  extends  also  into  the  organs  of  generation  in 
both  sexes,  and  into  the  ducts  of  the  glands  connected  with  them;  and 
in  the  female  becomes  continuous  with  the  serous  membrane  of  the  ab- 
domen at  the  fimbria?  of  the  Fallopian  tubes. 

Structure. — These  mucous  tracts,  and  different  portions  of  each  of 
them,  present  certain  structural  peculiarities  of  the  mucous  membrane, 
adapted  to  the  functions  which  each  part  has  to  discharge;  yet  in  some 
essential  characters  the  mucous  membrane  is  the  same,  from  whatever 
part  it  is  obtained.  In  all  the  principal  and  larger  parts  of  the  several 
tracts,  it  presents,  as  just  remarked,  an  external  layer  of  epithelium, 
situated  upon  a  basement  membrane,  and  beneath  this,  a  stratum  of  vas- 
cular tissue  of  variable  thickness,  containing  lymphatic  vessels  aud 
nerves.  The  vascular  stratum  or  corium,  together  with  the  basement 
membrane  and  epithelium,  in  different  cases,  is  elevated  into  minute 
papillae  and  villi,  or  depressed  into  involutions  in  the  form  of  glands. 
But  in  the  prolongations  of  the  tracts,  where  they  pass  into  gland-ducts, 
these  constituents  are  reduced  in  the  finest  branches  of  the  ducts  to  the 
epithelium,  the  primary  or  basemeut-membrane,  and  the  capillary  blood- 
vessels spread  over  the  outer  surface  of  the  latter  in  a  single  layer. 

The  primary  or  basement  membrane  is  a  thin,  transparent  layer,  sim- 
ple, homogeneous,  or  composed  of  endothelial  cells.  In  the  minuter 
divisions  of  the  mucous  membranes,  and  in  the  ducts  of  glands,  it  is  the 
layer  continuous  and  correspondent  with  this  basement-membrane  that 
forms  the  proper  walls  of  the  tubes.  The  cells  also  which,  lining  the 
larger  and  coarser  mucous  membranes,  constitute  their  epithelium,  are 
continuous  with,  and  often  similar  to  those  which,  lining  the  gland- 
ducts,  are  called  gland-cells.  No  certain  distinction  can  be  drawn  be- 
tween the  epithelium-cells  of  mucous  membranes  and  gland-cells. 

Mucous  Fluid :  Mucus. — From  all  mucous  membranes  there  is  se- 
creted either  from  the  surface  or  from  certain  special  glands,  or  from 
both,  a  more  or  less  viscid,  grayish,  or  semi-transpareut  fluid,  of  alka- 
line reaction  and  high  specific  gravity,  named  mucus.  It  mixes  imper- 
fectly with  water,  but,  rapidly  absorbing  liquid,  it  swells  considerably 
when  water  is  added.  Under  the  microscope  it  is  found  to  contain  epi- 
thelium and  leucocytes.  It  is  found  to  be  made  up,  chemically,  of  a 
nitrogenous  principle  called  mucin,  which  forms  its  chief  bulk,  of  a 
little  albumen,  of  salts  chiefly  chlorides  and  phosphates,  and  water  with 
traces  of  fats  and  extractives. 

Secreting  Glands. 

The  structure  of  the  elementary  portions  of  a  secreting  apparatus, 
namely  epithelium,  simple  membrane,  and  blond-vessels  having  been  al- 


330  HANDBOOK    OF   PHYSIOLOGY. 

ready  described  in  this  and  previous  chapters,  we  may  proceed  to  con- 
sider the  manner  in  which  they  are  arranged  to  form  the  varieties  of 
secreting  glands. 

The  secreting  glands  are  the  oi'gans  to  which  the  function  of  secretion- 
is  more  especially  ascribed ;  for  they  appear  to  be  occupied  with  it  alone. 
They  present,  amid  manifold  diversities  of  form  and  composition,  a  gen- 
eral plan  of  structure,  by  which  they  are  distinguished  from  all  other 
textures  of  the  body;  especially,  all  contain,  and  appear  constructed 
with  particular  regard  to,  the  arrangement  of  the  cells,  which,  as  already 
expressed,  both  line  their  tubes  or  cavities  as  an  epithelium,  and  elabo- 
rate, as  secreting  cells,  the  substances  to  be  discharged  from  them. 
Glands  are  provided  also  with  lymphatic  vessels  and  nerves.  The  distri- 
bution of  the  former  is  not  peculiar,  and  need  not  be  here  considered. 
!Nerve-fibres  are  distributed  both  to  the  blood-vessels  of  the  gland  and  to 
its  ducts;  and  to  the  secreting  cells  also  in  some  glands. 

Varieties. — 1.  The  simple  tubule  or  tubular  gland  (a,  Fig.  227),  ex- 
amples of  which  are  furnished  by  some  mucous  glands,  the  follicles  of 
Lieberkuhn,  and  the  tubular  glands  of  the  stomach.  These  appear  to 
be  simple  tubular  depressions  of  the  mucous  membrane,  the  wall  of  which 
is  formed  of  primary  membrane,  is  lined  with  secreting  cells  arranged  as 
an  epithelium.  To  the  same  class  may  be  referred  the  elongated  and 
tortuous  sudoriferous  glands. 

2.  The  compound  tubular  glands  (b,  Fig.  227)  form  another  division. 
These  consist  of  main  gland-tubes,  which  divide  and  subdivide.  Each 
gland  may  consist  of  the  subdivisions  of  one  or  more  main  tubes.  The 
ultimate  subdivisions  of  the  tubes  are  generally  highly  convoluted. 
They  are  formed  of  a  basement-membrane,  lined  by  epithelium  of  various 
forms.  The  larger  tubes  may  have  an  outside  coating  of  fibrous,  areolar, 
or  muscular  tissue.  The  Kidney,  Testis,  Salivary  glands,  Pancreas, 
Brunner's  glands  with  the  Lachrymal  and  Mammary  glands,  and  some 
Mucous  glands  are  examples  of  this  type,  but  present  more  or  less 
marked  variations  among  themselves 

3.  The  aggregate  or  racemose  glands,  in  which  a  number  of  vesicles  or 
acini  are  arranged  in  groups  or  lobules  (c,  Fig.  227).  The  Meibomian 
follicles  are  examples  of  this  kind  of  gland. 

These  various  organs  differ  from  each  other  only  in  secondary  points 
of  structure  ;  such  as,  chiefly,  the  arrangement  of  their  excretory  ducts, 
the  grouping  of  the  acini  and  lobules,  their  connection  by  areolar  tissue, 
and  supply  of  blood-vessels.  The  acini  commonly  appear  to  be  formed 
by  a  kind  of  fusion  of  the  walls  of  several  vesicles,  which  thus  combine 
to  form  one  cavity  lined  or  filled  with  secreting  cells  which  also  occupy 
recesses  from  the  main  cavity.  The  smallest  branches  of  the  gland-ducts 
sometimes  open  into  the  centres  of  these  cavities  ;  sometimes  the  acini 
are  clustered  round  the  extremities,  or  by  the  sides  of  the  ducts  :  but, 


SECRETION.  .>?>[ 

whatever  secondary  arrangement  there  may  be,  all  have  the  same  essen- 
tial character  of  rounded  groups  of  vesicles  containing  gland-cells,  and 
opening  by  a  common  central  cavity  into  minute  ducts,  which  ducts  in 
the  large  glands  converge  and  unite  to  form  larger  and  larger  branches, 
and  at  length  by  one  common  trunk,  open  on  a  free  surface  of  membrane. 
Among  these  varieties  of  structure,  all  the  secreting  glands  are  alike 
in  some  essential  points,  besides  those  which  they  have  in  common  with 


Fig.  227.— Plans  of  extension  of  secreting  membrane  by  inversion  or  recession  in  form  of  cavi- 
ties. A.  simple  glands,  viz.  g,  straight  tube;  h,  sac:  i.  coiled  tube.  B,  multilobular  crypts:  k.  of 
tubular  form :  /.saccular.  C,  racemose,  or  saccular  compound  gland:  »i.  entire  gland,  showing 
branched  duct  and  lobular  structure;  n.  a  lobule,  detached  with  o,  branch  of  duct  proceeding  from 
it.    D.  compound  tubular  gland  (Sharpey,). 


all  truly  secreting  structures.  They  agree  in  presenting  a  large  extent 
of  secreting  surface  within  a  comparatively  small  space;  in  the  circum- 
stance that  while  one  end  of  the  gland-duct  opens  on  a  free  surface,  the 
opposite  end  is  always  closed,  having  no  direct  communication  with 
blood-vessels,  or  any  other  canal;  and  in  a  uniform  arrangement  of  ca- 


332  HANDBOOK    OF   PHYSIOLOGY. 

pillary  blood-vessels,  ramifying  and  forming  a  network  around  the  walls 
and  in  the  interstices  of  the  ducts  and  acini. 

Process  of  Secretion. — In  secretion  two  distinct  processes  are  con- 
cerned which  may  be  spoken  of  as  I.  Physical,  and  II.  Chemical. 

1.  Physical  processes. — These,  already  discussed  in  the  last  chapter, 
are  such  as  can  be  closely  imitated  in  the  laboratory,  inasmuch  as  they 
consist  in  the  operation  of  well-known  physical  laws  ;  they  are — (a)  Fil- 
tration; (b)  Dialysis. 

(a)  Filtration  is,  as  we  have  already  mentioned,  simply  the  passage 
of  a  fluid  through  a  porous  membrane  under  the  influence  of  pressure. 
If  two  fluids  be  separated  by  a  porous  membrane,  and  the  pressure  on 
one  side  is  greater  than  on  the  other,  it  is  evident  that  in  the  absence  of 
counteracting  osmotic  influences  (see  below),  there  will  be  a  filtration 
through  the  membrane  until  the  pressure  on  the  two  sides  is  equalized. 
Of  course  there  may  be  fluid  only  on  one  side  of  the  membrane,  as  in  the 
ordinary  process  of  filtering  through  blotting-paper,  and  then  the  filtra- 
tion will  continue  as  long  as  the  pressure  (in  this  case,  the  weight  of  the 
fluid)  is  sufficient  to  force  it  through  the  pores  of  the  filter.  The  neces- 
sary inequality  of  pressure  may  be  obtained  either  by  diminishing  it  on 
one  side,  as  in  the  case  of  cupping ;  or  increasing  it  on  the  other,  as  in 
the  case  of  the  increased  blood-pressure,  and  consequent  increased  flow 
of  urine  resulting  from  copious  drinking.  By  filtration,  not  merely 
water,  but  various  salts  in  solution,  and  even  colloids  of  all  kinds,  may 
transude  from  the  blood-vessels.  The  amount  of  a  liquid  which  will 
pass  through  a  filter  in  a  given  time  depends  not  only  upon  the  amount 
of  pressure  to  which  it  is  subjected,  but  also  upon  the  nature  of  the 
fluid  filtered,  and  upon  the  kind  of  membrane  employed  as  the  filter. 
It  seems  probable  that  some  fluids,  such  as  the  secretions  of  serous  mem- 
branes, are  simply  exudations  or  oozings  (filtration)  from  the  blood- 
vessels, whose  qualities  are  determined  by  those  of  the  liquor  sanguinis, 
while  the  quantities  are  liable  to  variation,  and  are  chiefly  dependent 
upon  the  blood-pressure. 

(b)  Dialysis  is  the  passage  of  fluids  through  a  moist  animal  mem- 
brane independent  of  pressure,  and  sometimes  actually  in  opposition  to  it. 
There  must  always  be  in  this  process  two  fluids  differing  in  composition, 
one  or  both  possessing  an  affinity  for  the  intervening  membrane,  and  the 
fluids  must  be  capable  of  mixing  one  with  the  other  ;  the  osmotic  current 
continuing  in  each  direction  (when  both  fluids  have  an  affinity  for  the 
membrane)  until  the  chemical  composition  of  the  fluid  on  each  side  of 
the  septum  becomes  the  same. 

2.  Chemical  processes. — The  chemical  processes  constitute  the  process 
of  secretion,  properly  so  called,  as  distinguished  from  mere  transudation 
spoken  of  above.  In  the  chemical  process  of  secretion  various  materials 
which  do  not  exist  as  such  in  the  blood  are  elaborated  by  the  agency  of 


SECRETION.  33$ 

the  gland-cells  from  the  blood,  or  to  speak  more  accurately,  from  the 
plasma  which  exudes  from  the  blood-vessels  into  the  interstices  of  the 
gland-textures. 

The  best  evidence  in  favor  of  this  view  is  :  1st.  That  cells  and  nuclei 
are  constituents  of  all  glands,  nowever  diverse  their  outer  forms  and 
other  characters,  and  that  they  are  in  all  glands  placed  on  the  surface  or 
in  the  cavity  whence  the  secretion  is  poured.  2d.  That  many  secre- 
tions which  are  visible  with  the  microscope  may  be  seen  in  the  gland- 
cells  before  they  are  discharged.  Thus,  bile  may  be  often  discerned  by 
its  yellow  tinge  in  the  cells  of  the  liver;  spermatozoids  in  the  cells  of  the- 
tubules  of  the  testicles;  granules  of  uric  acid  in  those  of  the  kidneys  (of 
fish);  fatty  particles,  like  those  of  milk,  in  the  cells  of  the  mammary 
gland. 

Secreting  cells,  like  the  cells  or  other  elements  of  any  other  organ, 
appear  to  develop,  grow,  and  attain  their  individual  perfection  by  appro- 
priating nutriment  from  the  fluid  exuded  by  adjacent  blood-vessels  and 
elaborating  it,  so  that  it  shall  form  part  of  their  substance.  In  this  per- 
fected state,  the  cells  subsist  for  some  brief  time,  and  when  that  period 
is  over  they  appear  to  dissolve,  wholly  or  in  part,  and  yield  their  con- 
tents to  the  peculiar  material  of  the  secretion.  And  this  appears  to  be 
the  case  in  every  part  of  the  gland  that  contains  the  apjn-opriate  gland- 
cells  ;  therefore  not  in  the  extremities  of  the  ducts  or  in  the  acini  alone, 
but  in  great  part  of  their  length. 

We  have  described  elsewhere  the  changes  which  have  been  noticed 
from  actual  experiment  in  the  cells  of  the  salivary  glands,  pancreas,  and 
peptic  gland. 

Discharge  of  Secretions  from  glands  may  either  take  place  as  soon 
as  they  are  formed;  or  the  secretion  may  be  long  retained  within  the 
glands  or  its  ducts.  The  former  is  the  case  with  the  sweat  glands.  But 
the  secretions  of  those  glands  whose  activity  of  function  is  only  occasional 
are  usually  retained  in  the  cells  in  an  undeveloped  form  during  the 
periods  of  the  gland's  inaction.  And  there  are  glands  which  are  like 
both  these  classes,  such  as  the  lachrymal,  which  constantly  secrete  small 
portions  of  fluid,  and  on  occasions  of  greater  excitement  discharge  it 
more  abundantly. 

When  discharged  into  the  ducts,  the  further  course  of  secretions  is 
effected  (1)  partly  by  the  pressure  from  behind;  the  fresh  quantities  of 
secretion  propelling  those  that  were  formed  before.  In  the  larger  ducts, 
its  propulsion  is  (2)  assisted  by  the  contraction  of  their  walls.  All  the 
larger  ducts,  such  as  the  ureter  and  common  bile-duct,  possess  in  their 
coats  plain  muscular  fibres;  they  contract  when  irritated,  and  sometimes 
manifest  peristaltic  movements.  Rhythmic  contractions  in  the  pancre- 
atic and  bile-ducts  have  been  observed,  and  also  in  the  ureters  and  vasa 
deferentia.     It  is  probable  that  the  contractile  power  extends  along  the 


334  HANDBOOK    OF   PHYSIOLOGY. 

ducts  to  a  considerable  distance  within  the  substance  of  the  glands  whose 
secretions  can  be  rapidly  expelled.  Saliva  and  milk,  for  instance,  are 
sometimes  ejected  with  much  force. 

Circumstances  Influencing  Secretion. — The  principal  conditions 
which  influence  secretion  are  (1)  variations  in  the  quantity  of  blood,  (2) 
variations  in  the  quantity  of  the  peculiar  materials  for  any  secretion  that 
the  blood  may  contain,  and  (3)  variations  in  the  condition  of  the  nerves 
of  the  glands. 

(1.)  An  increase  in  the  quantity  of  blood  traversing  a  gland,  as  in 
nearly  all  the  instances  before  quoted,  coincides  generally  with  an  aug- 
mentation of  its  secretion.  Thus,  the  mucous  membrane  of  the  stomach 
becomes  florid  when,  on  the  introduction  of  food,  its  glands  begin  to  se- 
crete; the  mammary  gland  becomes  much  more  vascular  during  lactation; 
and  all  circumstances  which  give  rise  to  an  increase  in  the  quantity  of 
material  secreted  by  an  organ  produce,  coincidently,  an  increased  supply 
of  blood;  but  we  have  seen  that  a  discharge  of  saliva  may  occur  under 
extraordinary  circumstances,  without  increase  of  blood-supply,  and  so  it 
may  be  inferred  that  this  condition  of  increased  blood-supply  is  not  abso- 
lutely essential. 

(2.)  An  increase  in  the  amount  of  the  materials  which  the  glands  are 
designed  to  separate  or  elaborate,  contained  in  the  blood  supplied  to  them, 
increases  the  amount  of  any  secretion.  Thus,  when  an  excess  of  nitro- 
genous waste  is  in  the  blood,  whether  from  excessive  exercise,  or  from 
destruction  of  one  kidney,  a  healthy  kidney  will  excrete  more  urea  than 
it  did  before. 

(3.)  Influence  of  the  Nervous  System  on  Secretion. — The  process  of 
secretion  is  largely  influenced  by  the  condition  of  the  nervous  system. 
The  exact  mode  in  which  the  influence  is  exhibited  must  still  be  regarded 
as  somewhat  obscure.  In  part,  it  exerts  its  influence  by  increasing  or 
diminishing  the  quantity  of  blood  supplied  to  the  secreting  gland,  in 
virtue  of  the  power  which  it  exercises  over  the  contractility  of  the  smaller 
blood-vessels;  while  it  also  has  a  more  direct  influence,  as  was  described 
at  length  in  the  case  of  the  submaxillary  gland,  upon  the  secreting  cells 
themselves;  this  may  be  called  trophic  influence.  Its  influence  over  se- 
cretion, as  well  as  over  other  functions  of  the  body,  may  be  excited  by 
causes  acting  directly  upon  the  nervous  centres,  upon  the  nerves  going 
to  the  secreting  organ,  or  upon  the  nerves  of  other  parts.  In  the  latter 
case,  a  reflex  action  is  produced:  thus  the  impression  produced  upon  the 
nervous  centres  by  the  contact  of  food  in  the  mouth,  is  reflected  upon 
the  nerves  supplying  the  salivary  glands,  and  produces,  through  these,  a 
more  abundant  secretion  of  the  saliva. 

Through  the  nerves,  various  conditions  of  the  brain  also  influence  the 
secretions.  Thus,  the  thought  of  food  may  be  sufficient  to  excite  an 
abundant  flow  of  saliva.     And,  probably,  it  is  the  mental  state  which 


SECRETION. 


;:;:> 


excites  the  abundant  secretion  of  urine  in  hysterical  paroxysms,  as  well 
as  the  perspirations,  and,  occasionally,  diarrhoea,  which  ensue  under  the 
influence  of  terror,  and  the  tears  excited  by  sorrow  or  excess  of  joy.  The 
quality  of  a  secretion  may  also  be  affected  by  mental  conditions,  as  in 
the  cases  in  which,  through  grief  or  passion,  the  secretion  of  milk  is  al- 
tered, and  is  sometimes  so  changed  as  to  produce  irritation  in  the  ali- 
mentary canal  of  the  child,  or  even  death  (Carpenter). 

Relations  between  the  Secretions. — The  secretions  of  some  of 
the  glands  seem  to  bear  a  certain  relation  or  antagonism  to  each  other, 
by  which  an  increased  activity  of  one  is  usually  followed  by  diminished 
activity  of  one  or  more  of  the  others;  and  a  deranged  condition  of  one 
is  apt  to  entail  a  disordered  state  in  the  others.  .  Such  relations  appear 
to  exist  among  the  various  mucous  membranes;  and  the  close  relation 
between  the  secretion  of  the  kidney  aud  that  of  the  skin  is  a  subject  of 
constant  observation. 


The  Mammary  Glands. 

Structure. — The  mammary  glands  are  composed  of  large  divisions  or 
lobes,  and  these  are  again  divisible  iuto  lobules,  the  lobules  being  coni- 


FiG.  228.— Dissection  of  the  lower  half  of  the  female  mamma  during  the  period  of  lactation. 
%.— In  the  left  hand  side  of  the  dissected  part  the  glandular  lobes  are  exposed  and  partially 
unravelled;  and  on  the  right-hand  side,  the  glandular  substance  has  been  removed  to  snow  the 
reticular  loculi  of  the  connective  tissue  in  which  the  glandular  lobules  are  placed:  1,  upper  part  of 
the  mamilla  or  nipple;  2,  areola;  3,  subcutaneous  masses  of  fat;  4,  reticular  loculi  of  the  connective 
tissue  which  support  the  glandular  substance  and  contain  the  fatty  masses;  5,  one  of  three  lac- 
tiferous ducts  shown  passing  towards  the  mamilla  where  they  open";  Cone  of  the  sinus  laetei  or 
reservoirs;  7,  some  of  the  glandular  lobules  which  have  been  unravelled;  7\  others  massed  together 
(Luschka). 

posed  of  the  convoluted  subdivision  of  the  main  ducts  (alveoli).     The 


336  HANDBOOK    OF    PHYSIOLOGY. 

lobes  and  lobules  are  bound  together  by  areolar  tissue;  penetrating  be- 
tween tbe  lobes,  and  covering  the  general  surface  of  the  gland,  with  the 
exception  of  the  nipple,  is  a  considerable  quantity  of  yellow  fat,  itself 
lobulated  by  sheaths  and  processes  of  tough  areolar  tissue  (Fig.  228) 
connected  both  with  the  skin  in  front  and  the  gland  behind;  the  same 
bond  of  connection  extending  also  from  the  under  surface  of  the  gland 
to  the  sheathing  connective  tissue  of  the  great  pectoral  muscle  on  which 
it  lies.  The  main  ducts  of  the  gland,  fifteen  to  twenty  in  number, 
called  the  lactiferous  or  galactophorous  ducts,  are  formed  by  the  union 
of  the  smaller  (lobular)  ducts,  and  open  by  small  separate  orifices 
through  the  nipple.  At  the  points  of  junction  of  lobular  ducts  to  form 
lactiferous  ducts,  and  just  before  these  enter  the  base  of  the  nipple,  the 
ducts  are  dilated  (Fig.  228);  and,  during  lactation,  the  period  of  active 
secretion  by  the  gland,  the  dilatations  form  reservoirs  for  the  milk, 
which  collects  in,  and  distends  them.  The  walls  of  the  gland-ducts  are 
formed  of  areolar  with  some  unstriped  muscular  tissue,  and  are  lined 
internally  by  short  columnar,  and  near  the  nipple  by  squamous  epithe- 
lium. The  alveoli  consist  of  a  membrana  propria  of  flattened  endothe- 
lial cells  lined  by  low  columnar  epithelium,  and  are  filled  with  fat 
globules. 

The  nipple,  which  contains  the  terminations  of  the  lactiferous  ducts, 
is  composed  also  of  areolar  tissue,  and  contains  unstriped  muscular  fibres. 
Blood-vessels  are  also  freely  supplied  to  it,  so  as  to  give  it  a  species  of 
erectile  structure.  On  its  surface  are  very  sensitive  papillae;  and  around 
it  is  a  small  area,  or  areola,  of  pink  or  dark-tinted  skin,  on  which  are  to 
be  seen  small  projections  formed  by  minute  secreting  glands. 

Blood-vessels,  nerves,  and  lymphatics  are  plentifully  supplied  to  the 
mammary  glands;  the  calibre  of  the  blood-vessels,  as  well  as  the  size  of 
the  glands,  varying  very  greatly  under  certain  conditions,  especially 
those  of  pregnancy  and  lactation. 

Changes  in  the  Glands  at  certain  Periods. — The  minute  changes 
which  occur  in  the  mammary  gland  during  its  periods  of  evolution  (preg- 
nancy), and  involution  (when  lactation  has  ceased),  are  the  following: 

The  most  favorable  period  for  observing  the  epithelium  of  the  mam- 
mary gland  fully  developed  is  shortly  before  the  end  of  pregnancy.  At 
this  period  the  acini  which  form  the  lobules  of  the  gland,  are  found  to 
be  lined  with  a  mosaic  of  polyhedral  epithelial  cells  (Fig.  229),  and  sup- 
ported by  a  connective-tissue  stroma. 

The  rapid  formation  of  milk  during  lactation  results  from  a  fatty 
metamorphosis  of  the  epithelial  cells. 

In  the  earlier  days  of  lactation,  epithelial  cells  partially  transformed 
are  discharged  in  the  secretion:  these  are  termed  "colostrum  cor- 
puscles," but  later  on  the  cells  are  completely  transformed  into  fat  be- 
fore the  secretion  is  discharged. 


SECRETION. 


337 


After  the  end  of  lactation,  the  mamma  gradually  returns  to  its  ori- 
ginal size  (involution).  The  acini,  in  the  early  stages  of  involution,  are 
lined  with  cells  in  all  degrees  of  vacuolation.  As  involution  proceeds 
the  acini  diminish  considersbly  in  size,  and  at  length,  instead  of  a 
mosaic  of  lining  epithelial  cells  (twenty  to  thirty  in  each  acinus),  we 
have  five  or  six  nuclei  (some  with  no  surrounding  protoplasm)  lying  in 
an  irregular  heap  within  the  acinus.  During  the  later  stages  of  involu- 
tion, large,  yellow  granular  cells  are  to  be  seen.  As  the  acini  diminish 
in  size,  the  connective  tissue  and  fatty  matter  between  them  increase, 
and  in  some  animals,  when  the  gland  is  completely  inactive,  it  is  found 
to  consist  of  a  thin  film  of  glandular  tissue  overlying  a  thick  cushion  of 
fat.     Many  of  the  produces  of  waste  are  carried  off  by  the  lymphatics. 

During  pregnancy  the  mammary  glands  and  mammas  undergo 
changes  (evolution)  which  are  readily  observable.  They  enlarge,  become 
harder  and  more  distinctly  lobulated:  the  veins  on  the  surface  become 
more  prominent.     The  areola  becomes  enlarged  and  dusky,  with  pro- 


Fig.  229.— Section  of  mammary  gland  of  bitch,  showing  acini,  lined  with    epithelial  cells  of  a 
polyhedral  or  short  columnar  form.     X  200.     (.V.  D.  Harris.) 

jecting  papillse;  the  nipple  too  becomes  more  prominent,  and  milk  can 
be  squeezed  from  the  orifices  of  the  ducts.  This  is  a  very  gradual  pro- 
cess, which  commences  about  the  time  of  conception,  and  progresses 
steadily  during  the  whole  period  of  gestation.  The  acini  enlarge,  and  a 
series  of  changes  occur,  exactly  the  reverse  of  those  just  described  under 
the  head  of  Involution. 


The  Mammary  Secretion  :  Milk. 

The  secretion  of  the  mammary  glands,  or  milk,  is  a  bluish-white 
opaque  fluid  with  a  pleasant  sweet  taste.  It  is  a  true  emulsion.  Under 
the  microscope,  it  is  found  to  contain  a  number  of  globules  of  various 
sizes  (Fig.  230),  the  majority  about  TTr$inr  of  an  inch  in  diameter.  They 
are  composed  of  oily  matter,  probably  coated  by  a  fine  layer  of  albumi- 
nous material,  and  are  called  milk-globules;  while,  accompanying  these, 
are  numerous  minute  particles,  both  oily  and  albuminous,  which  exhibit 


338  HANDBOOK    OF    PHYSIOLOGY. 

ordinary  molecular  movements.  The  milk  which  is  secreted  in  the  first 
few  days  after  parturition,  and  which  is  called  the  colostrum,  differs  from 
ordinary  milk  in  containing  a  larger  quantity  of  solid  matter;  and  under 
the  microscope  are  to  be  seen  certain  granular  masses  called  colostrum- 
corpuscles.  These,  which  appear  to  be  small  masses  of  albuminous  and 
oily  matter,  are  probably  secreting  cells  of  the  gland,  either  in  a  state  of 
fatty  degeneration,  or  old  cells  which  in  their  attempt  at  secretion  under 
the  new  circumstances  of  active  need  of  milk,  are  filled  with  oily  matter; 
which,  however,  being  unable  to  discharge,  they  are  themselves  shed 
bodily  to  make  room  for  their  successors.  Colostrum-corpuscles  have 
been  seen  to  exhibit  contractile  movements  and  to  squeeze  out  drops  of 
oil  from  their  interior. 

Chemical  Composition. — In  addition  to  the  oil  existing  in  numberless 
little  globules,  coated  with  a  thin  layer  of  albuminous  matter,  floating 


a, 

Fia.  230.— Globules  and  molecules  of  Cow's  milk,    x  400. 

in  a  large  quantity  of  water,  milk  contains  casein,  serum-albumin,  milk- 
sugar  (lactose),  and  several  salts.  Its  percentage  composition  has  been 
already  mentioned,  but  may  be  here  repeated.  Its  reaction  is  alkaline: 
its  specific  gravity  about  1030. 

Table  of  the  Chemical  Composition  of  Milk. 

Human.  Cow. 

Water,  ....         890         ....     858 
Solids,       .         .         .         .     110     .         .         .         .142 


1000  1000 

Human.  Cow. 
Proteids,  including  Casein 

and  Serum-Albumin,  .         35  ....       68 

Fats  or  Butter,                           25     .  38 

Sugar  (with  extractives),          48  .         .         .30 


BBCJSETION.  33;) 


Salts  (chiefly  potassium, 
sodium,  and  calcium, 
chlorides  and  phos- 
phates), 


110  142 


When  milk  is  allowed  to  stand,  the  fat  globules,  being  the  lightest 
portion,  rise  to  the  top,  forming  cream.  If  a  little  acetic  acid  be  added 
to  a  drop  of  milk  under  the  microscope,  the  albuminous  film  coating  the 
oil  drops  is  dissolved,  and  they  run  together  into  larger  drops.  The 
same  result  is  produced  by  the  process  of  churning,  the  effect  of  which 
is  to  break  up  the  albuminous  coating  of  the  oil  drops:  they  then  coalesce 
to  form  butter. 

Curdling  of  Milk. — The  curdling  of  milk  is  due  to  the  coagulation 
of  the  casein  which  is  kept  in  solution  under  normal  conditions  by  the 
alkaline  calcium  phosphate.  On  the  addition  of  an  acid,  such  as  acetic, 
the  casein  is  precipitated.  This  occurs,  too,  if  it  be  allowed  to  stand  for 
some  time,  its  reaction  becomes  acid:  in  popular  language  it  " turns 
sour.'"  The  change  appears  to  be  due  to  the  conversion  of  the  milk-sugar 
into  lactic  acid,  by  means]of  a  special  micro-organism,  Bacterium  lactis; 
this  causes  the  precipitation  (curdling)  of  the  casein:  the  curd  contains 
the  fat  globules:  the  remaining  fluid  (whey)  consists  of  water  holding 
in  solution  albumen,  milk-sugar,  and  certain  salts.  The  same  effect  is 
produced  in  the  manufacture  of  cheese,  which  is  really  casein  coagulated 
by  the  agency  of  rennet  (p.  254).  When  milk  is  boiled,  the  scum  which 
forms  consists  chiefly  of  serum-albumint 

Curdling  Ferments. — The  effect  of  the  ferments  of  the  gastric, 
pancreatic,  and  intestinal  juices  in  curdling  milk  {curdling  ferments) 
has  already  been  mentioned  in  the  Chapter  on  Digestion. 

The  salts  of  milk  are  chlorides,  sulphates,  phosphates,  and  carbo- 
nates of  potassium,  sodium,  and  calcium. 

Traces  of  iron,  fluorine,  and  silica  are  also  found,  and  the  gases,  car- 
bonic acid,  oxygen,  and  nitrogen. 


CHAPTER    XL 

THE  STRUCTURE  AND  FUNCTIONS   OF  THE   SKIN. 

The  skin  serves — (1),  as  an  external  integument  for  the  protection 
of  the  deeper  tissues,  and  (2),  as  a  sensitive  organ  in  the  exercise  of 
touch;  it  is  also  (3),  an  important  secretory  and  excretory,  and  (4),  an 
absorbing  organ;  while  it  plays  an  important  part  in  (5)  the  regulation 
of  the  temperature  of  the  body. 

Structure. — The  skin  consists,  principally,  of  a  vascular  tissue  named 
the  corium,  derma,  or  cutis  vera,  and  an  external  covering  of  epithelium 
termed  the  cuticle  or  epidermis.  Within  and  beneath  the  corium  are 
imbedded  several  organs  with  special  function,  namely,  sudoriferous 
glands,  sebaceous  glands,  and  hair  follicles  ;  and  on  its  surface  are  sen- 
sitive papittce.  The  so-called  appendages  of  the  skin — the  hair  and 
nails — are  modifications  of  the  epidermis. 

A.  Epidermis. — The  epidermis  is  composed  of  several  strata  of  cells 
of  various  shapes  and  sizes;  it  closely  resembles  in  its  structure  the  epi- 
thelium of  the  mucous  membrane  that  lines  the  mouth.  The  following 
four  layers  may  be  distinguished  in  a  more  or  less  developed  form.  1. 
Stratum  corneum  (Fig.  231,  a),  consisting  of  superposed  layers  of  horny 
scales.  The  different  thickness  of  the  epidermis  in  different  regions  of 
the  body  is  chiefly  due  to  variations  in  the  thickness  of  this  layer;  e.  g., 
on  the  horny  parts  of  the  palms  of  the  hands  and  soles  of  the  feet  it  is 
of  great  thickness.  The  stratum  corneum  of  the  buccal  epithelium 
chiefly  differs  from  that  of  the  epidermis  in  the  fact  that  nuclei  are  to 
be  distinguished  in  some  of  the  cells  even  of  its  most  superficial  layers. 

2.  Stratum  lucidum,  a  bright  homogeneous  membrane  consisting  of 
squamous  cells  closely  arranged,  in  some  of  which  a  nucleus  can  be  seen. 

3.  Stratum  granulosum,  consisting  of  one  layer  of  flattened  cells 
which  appear  fusiform  in  vertical  section:  they  are  distinctly  nucleated, 
and  a  number  of  granules  extend  from  the  nucleus  to  the  margins  of  the 
cell. 

4.  Stratum  Malpighii  or  Rete  mucosum  consists  of  many  strata. 
The  deepest  cells,  placed  immediately  above  the  cutis  vera,  are  columnar 
with  oval  nuclei:  this  layer  of  columnar  cells  is  succeeded  by  a  number 
of  layers  of  more  or  less  polyhedral  cells  with  spherical  nuclei;  the  cells 


THE    STRUCTURE    AND    FUNCTIONS    OF    THE    SKIN. 


341 


■of  the  more  superficial  layers  are  considerably  flattened.  The  deeper 
surface  of  the  rete  mucosum  is  accurately  adapted  to  the  papilla3  of  the 
true  skin,  being,  as  it  were,  moulded  on  them.  It  is  very  constant  in 
thickness  in  all  parts  of  the  skin.  The  cells  of  the  middle  layers  of  the 
stratum  Malpighii  are  almost  all  connected  by  processes,  and  thus  form 
"  prickle  cells  "  (Fig.  27).  The  pigment  of  the  skin,  the  varying  quan- 
tity of  which  causes  the  various  tints  observed  in  different  individuals 
and  different  races,  is  contained  in  the  deeper  cells  of  rete  mucosum; 
the  pigmented  cells  as  they  approach  the  free  surface  gradually  losing 
their  color.  Epidermis  maintains  its  thickness  in  spite  of  the  constant 
■wear  and  tear  to  which  it  is  subjected.     The  columnar  cells  of  the  deep- 


Fig.  231. 


Fig.  232. 


Fig.  231.— Vertical  section  of  the  epidermis  of  the  prepuce,  a.  stratum  corneum,  of  very  few- 
layers,  the  stratum  lucidum  and  stratum  granulosum  not  being  distinctly  represented ;  b,  c,  d,  and 
€.  the  layers  of  the  stratum  Malpighii,  a  certain  number  of  the  cells  in  layers  d  and  e  showing  signs 
of  segmentation;  layer  c  consists  chiefly  of  prickle  or  ridge  and  furrow  cells:  /,  basement  mem- 
brane; g,  cells  in  cutis  vera.    ( Cadiat. ) 

Fig.  232. -Vertical  section  of  skiu  of  the  negro,  a,  a.  Cutaneous  papillae,  b.  Undermost  and 
dark-colored  layer  of  oblong  vertical  epidermis-cells,  c.  Stratum  Malpighii.  d.  Superficial  layers, 
including  stratum  corneum,  stratum  lucidum,  and  stratum  granulosum,  the  last  two  not  differen- 
tiated in  fig.     x  250.    (Sharpey.) 


est  layer  of  the  "rete  mucosum"  elongate,  and  their  nuclei  divide  into 
two  (Fig.  231,  e).  Lastly,  the  upper  part  of  the  cell  divides  from  the 
lower;  thus  from  a  long  columnar  cell  are  produced  a  polyhedral  and  a 
short  columnar  cell:  the  latter  elongates  and  the  process  is  repeated. 
The  polyhedral  cells  thus  formed  are  pushed  up  towards  the  free  surface 
by  the  production  of  fresh  ones  beneath  them,  and  become  flattened  from 
pressure:  they  also  become  gradually  horny  by  evaporation  and  trans;- 


342  HANDBOOK    OF    PHYSIOLOY. 

formation  of  their  protoplasm  into  keratin,  till  at  last  by  rubbing  they 
are  detached  as  dry  horny  scales  at  the  free  surface.  There  is  thus  a 
constant  production  of  fresh  cells  in  the  deeper  layers,  and  a  constant 
throwing  off  of  old  ones  from  the  free  surface.  When  these  two  pro- 
cesses are  accurately  balanced,  the  epidermis  maintains  its  thickness. 
When,  by  intermittent  pressure  a  more  active  cell-growth  is  stimulated, 
the  production  of  cells  exceeds  their  waste  and  the  epidermis  increases 
in  thickness,  as  we  see  in  the  horny  hands  of  the  laborer. 

The  thickness  of  the  epidermis  on  different  portions  of  the  skin  is 
directly  proportioned  to  the  friction,  pressure,  and  other  sources  of 
injury  to  which  it  is  exposed;  for  it  serves  as  well  to  protect  the  sensi- 
tive and  vascular  cutis  from  injury  from  without,  as  to  limit  the  evapo- 
ration of  fluid  from  the  blood-vessels.  The  adaptation  of  the  epidermis 
to  the  latter  purposes  may  be  well  shown  by  exposing  to  the  air  two  dead 
hands  or  feet,  of  which  one  has  its  epidermis  perfect,  and  the  other  is 
deprived  of  it;  in  a  day,  the  skin  of  the  latter  will  become  brown,  dry, 
and  horn-like,  while  that  of  the  former  will  almost  retain  its  natural 
moisture. 

B.  Cutis  vera. — The  corium  or  cutis  vera,  which  rests  upon  a  layer 
of  adipose  and  cellular  tissue  of  varying  thickness,  is  a  dense  and  tough, 
but  yielding  and  highly  elastic  structure,  composed  of  fasciculi  of  are- 
olar tissue,  interwoven  in  all  directions,  and  forming  by  their  interlace- 
ments, numerous  spaces  or  areolae.  These  areolae  are  large  in  the  deeper 
layers  of  the  cutis,  and  are  there  usually  filled  with  little  masses  of  fat 
(Fig.  234):  but,  in  the  superficial  parts,  they  are  small  or  entirely  ob- 
literated.    Plain  muscular  fibres  are  also  abundantly  present. 

Papillae. — The  cutis  vera  presents  numerous  conical  elevations,  or 
papillce,  with  a  single  or  divided  free  extremity,  which  are  more  promi- 


Fig.  233.— Compound  papillae  from  the  palm  of  the  hand,  a,  basis  of  a  papilla;  6,  b,  divisions 
or  branches  of  the  same;  c,  c,  branches  belonging  to  papilla?,  of  which  the  bases  are  hidden  from 
view,    x  60.    CKolliker.) 

nent  and  more  densely  set  at  some  parts  than  at  others  (Fig.  233).  This 
is  especially  the  case  on  the  palmar  surface  of  the  hands  and  fingers,  and 
on  the  soles  of  the  feet — parts,  therefore,  in  which  the  sense  of  touch  is 
most  acute.     On  these  parts  they  are  disposed  in  double  rows,  in  parallel 


THE    STRUCTURE    AND    FUNCTIONS    OF   THE    SKIN. 


343 


curved  lines,  separated  from  each  other  by  depressions.  Thus  they  may 
be  easily  seen  on  the  palm,  whereon  each  raised  line  is  composed  of  a 
double  row  of  papillae,  and  is  intersected  by  short  transverse  lines  or  fur- 
rows corresponding  with  the  interspaces  between  the  successive  pairs  of 
papillae.  Over  other  parts  of  the  skin  they  are  more  or  less  thinly  scat- 
tered, and  are  scarcely  elevated  above  the  surface.     Their  average  length 


Fig.  234.— Vertical  section  of  skin.  A.  Sebaceous  gland  opening  into  hair  follicle.  B.  Muscular 
fibres.  C.  Sudoriferous  or  sweat-gland.  D.  Subcutaneous  fat.  E.  Fundus  of  hair-follicle,  with 
hair-papillae.    CKlein  and  Noble  Smith.) 


is  about  yJpj-  of  an  inch,  and  at  their  base  they  measure  about  tj-^o  of  an 
inch  in  diameter.  Each  papilla  is  abundantly  supplied  with  blood,  re- 
ceiving from  the  vascular  plexus  in  the  cutis  one  or  more  minute  arterial 
twigs,  which  divide  into  capillary  loops  in  its  substance,  and  then  re- 
unite into  a  minute  vein,  which  passes  out  at  its  base.  This  abundant 
supply  of  blood  explains  the  turgescence  or  kind  of  erection  which  they 
undergo  when  the  circulation  through  the  skin  is  active.     The  majority, 


344 


HANDBOOK    OF   PHYSIOLOGY. 


but  not  all,  of  the  papillae  contain  also  one  or  more  terminal  nerve-fibres 
from  the  ultimate  ramifications  of  the  cutaneous  plexus,  on  which  their 
exquisite  sensibility  depends. 

The  nerve-terminations  in  the  skin  are  described  under  the  Sen- 
sory Nerve  Terminations. 

Glands  of  the  Skin. — The  skin  possesses  glands  of  two  kinds;  (a) 
Sudoriferous,  or  Sweat  Glands;  (b)  Sebaceous  Glands. 

(a)  Sudoriferous,  or  Sweat  Glands. — Each  of  these  glands  consists  of 
a  small  lobular  mass,  formed  of  a  coil  of  tubular  gland-duct,  surrounded 
by  blood-vessels  and  imbedded  in  the  subcutaneous  adipose  tissue  (Fig. 
234,  C).  From  this  mass  the  duct  ascends,  for  a  short  distance,  in  a 
spiral  manner  through  the  deeper  part  of  the  cutis,  then  passing  straight, 
and  then  sometimes  again  becoming  spiral,  it  passes  through  the  cuticle 
and  opens  by  an  oblique  valve-like  aperture.  In  the  parts  where  the 
epidermis  is  thin,  the  ducts  themselves  are  thinner,  and  more  nearly 


Fig.  235.— Terminal  tubules  of  sudoriferous  glands,  cut  in  various  directions  from  the  skin  of 
the  pig's  ear.    (Y.  D.  Harris.) 


straight  in  their  course  (Fig.  234).  The  duct,  which  maintains  nearly 
the  same  diameter  throughout,  is  lined  with  a  layer  of  columnar  epithe- 
lium (Fig.  235)  continuous  with  the  epidermis;  while  the  part  which 
passes  through  the  epidermis  is  composed  of  the  latter  structure  only; 
the  cells  which  immediately  form  the  boundary  of  the  canal  in  this  part 
being  somewhat  differently  arranged  from  those  of  the  adjacent  cuticle. 
The  coils  or  terminal  portions  of  the  gland  are  lined  with  at  least  two 
layers  of  short  columnar  cells  with  very  distinct  nuclei  (Fig.  235),  and 
possess  a  large  lumen  distinctly  bounded  by  a  special  lining  or  cuticle. 

The  sudoriferous  glands  are  abundantly  distributed  over  the  whole 
surface  of  the  body,  but  are  especially  numerous,  as  well  as  very  large, 
in  the  skin  of  the  palm  of  the  hand,  and  of  the  sole  of  the  foot.  The 
glands  by  which  the  peculiar  odorous  matter  of  the  axilhe  is  secreted 
form  a  nearly  complete  layer  under  the  cutis,  and  are  like  the  ordinary 


THE    STRUCTURE    AM)    FUNCTIONS    OF   THE    SKIN.  345 

sudoriferous  glands,  except  in  being  larger,  and  having  very  short 
ducts. 

The  peculiar  bitter  yellow  substance  secreted  by  the  skin  of  the  ex- 
ternal auditory  passage  is  named  cerumen,  and  the  glands  themselves 
ceruminous  glands;  but  they  do  not  much  differ  in  structure  from  the 
ordinary  sudoriferous  glands. 

(b)  Sebaceous  Glands. — The  sebaceous  glands  (Fig.  236),  like  the 
sudoriferous  glands,  are  abundantly  distributed  over  most  parts  of  the 
body.  They  are  most  numerous  in  parts  largely  supplied  with  hair,  as 
the  scalp  and  face,  and  are  thickly  distributed  about  the  entrances  of 


Fig.  236.— Sebaceous  gland  from  human  skin.    (TClein  and  Noble  Smith.) 

the  various  passages  into  the  body,  as  the  anus,  nose,  lips,  and  external 
ear.  They  are  entirely  absent  from  the  palmar  surface  of  the  hand  and 
the  plantar  surfaces  of  the  feet.  They  are  minutely  lobulated  glands 
composed  of  an  aggregate  of  small  tubes  or  sacculi  filled  with  opaque 
white  substances,  like  soft  ointment.  Minute  capillary  vessels  overspread 
them;  and  their  ducts  open  either  on  the  surface  of  the  skin,  close  to  a 
hair,  or,  which  is  more  usual,  directly  into  the  follicle  of  the  hair.  In 
the  latter  case,  there  are  generally  two  or  more  glands  to  each  hair  (Fig. 
234). 

Hair.  — A  hair  is  produced  by  a  peculiar  growth  and  modification  of 
the  epidermis.  Externally  it  is  covered  by  a  layer  of  fine  scales  closely 
imbricated,  or  overlapping  like  the  tiles  of  a  house,  but  with  the  free 
edges  turned  upwards  (Fig.  237,  a).     It  is  called  the  cuticle  of  the  hair. 


346  HANDBOOK    OF    PHYSIOLOGY. 

Beneath  this  is  a  much  thicker  layer  of  elongated  horny  cells,  closely 
packed  together  so  as  to  resemble  a  fibrous  structure.  This,  very  com- 
monly, in  the  human  subject,  occupies  the  whole  of  the  inside  of  the 
hair;  but  in  some  cases  there  is  left  a  small  central  space  filled  by  a  sub- 
stance called  the  medulla  or  pith,  composed  of  small  collections  of  irreg- 
ularly shaped  cells,  containing  sometimes  pigment  granules  or  fat,  but 
mostly  air. 

The  follicle,  in  which  the  root  of  each  hair  is  contained  (Fig.  238), 
forms  a  tubular  depression  from  the  surface  of  the  skin,  descending  into 
the  subcutaneous  fat,  generally  to  a  greater  depth  than  the  sudoriferous 
glands,  and  at  its  deepest  part  enlarging  in  a  bulbous  form,  and  often 
curving  from  its  previous  rectilinear  course.  It  is  lined  throughout  by 
cells  of  epithelium,  continuous  with  those  of  the  epidermis,  and  its 
walls  are  formed  of  pellucid  membrane,  which  commonly,  in  the  folli- 
cles of  the  largest  hairs,  has  the  structure  of  vascular  fibrous  tissue.  At 
the  bottom  of  the  follicle  is  a  small  papilla,  or  projection  of  true  skin, 


Fig.  237.— Surf  ace  of  a  white  hair,  magnified  160  diameters.  The  wave  lines  mark  the  upper  or 
free  edges  of  the  cortical  scales.    B,  separated  scales,  magnified  350  diameters.    (Kolliker.) 

and  it  is  by  the  production  and  outgrowth  of  epidermal  cells  from  the 
surface  of  this  papilla  that  the  hair  is  formed.  The  inner  wall  of  the 
follicle  is  lined  by  epidermal  cells  continuous  with  those  covering  the 
general  surface  of  the  skin;  as  if  indeed  the  follicle  had  been  formed  by 
a  simple  thrusting  in  of  the  surface  of  the  integument  (Fig.  238).  This 
epidermal  lining  of  the  hair-follicle,  or  root-sheath  of  the  hair,  is  com- 
posed of  two  layers,  the  inner  one  of  which  is  so  moulded  on  the  im- 
bricated scaly  cuticle  of  the  hair,  that  its  inner  surface  becomes  imbri- 
cated also,  but  of  course  in  the  opposite  direction.  When  a  hair  is  pulled 
out,  the  inner  layer  of  the  root-sheath  and  part  of  the  outer  layer  also, 
are  commonly  pulled  out  with  it. 

Nails. — A  nail,  like  a  hair,  is  a  peculiar  arrangement  of  epidermal 
cells,  the  undermost  of  which,  like  those  of  the  general  surface  of  the 
integument,  are  rounded  or  elongated,  while  the  superficial  are  flattened, 
and  of  more  horny  consistence.  That  specially  modified  portion  of  the 
corium,  or  true  skin,  by  which  the  nail  is  secreted,  is  called  the  matrix. 

The  back  edge  of  the  nail,  or  the  root  as  it  is  termed,  is  received  into 
a  shallow  crescentic  groove  in   the  matrix,  while  the  front  part  is  free 


THE    STRUCTURE  AND    FUNCTIONS    OF    THE   SKIN. 


U~ 


and  projects  beyond  the  extremity  of  the  digit.  The  intermediate  por- 
tion of  the  nail  rests  by  its  broad  under  surface  on  the  front  part  of  the 
matrix,  which  is  here  called  the  bed  of  the  nail.  This  part  of  the  matrix 
is  not  uniformly  smooth  on  the  surface,  but  is  raised  in  the  form  of  longi- 
tudinal and  nearly  parallel  ridges  or  laminae,  on  which  are  moulded  the 
epidermal  cells  of  which  the  nail  is  made  up  (Fig.  241). 

The  growth  of  the  nail,  like  that  of  the  hair,  or  of  the  epidermis 
generally,  is  effected  by  a  constant  production  of  cells  from  beneath  and 
behind,  to  take  the  place  of  those  which  are  worn  or  cut  away.     Inas- 


•JjC   ([' 


r^iU 


Av 


Fig.  238.  FlG-  239- 

■cv„  <m«  Mpiiium  si7P>l  hair  in  its  follicle,  o,  stem  cut  short;  b,  root;  c,  knob;  d.  hair  cuticle; 
e  teM^fXSKK  dermic  coat  of  follicle;  /papilla:  A-.  k  ducts  of  sebace- 
ous  Snds;T  corium ;  », ,  mucous  layer  of  epidermis ;  o,  upper  limit  of  internal  root  sheath,    x  50. 

,K  pfef^jL  -Longitudinal  section  of  a  hair  follicle,    rr,  Stratum  of  Malpifrhi  deep  layer  forming 

medu»a.ysheatiroi  medulla;/,  hair  papilla;  ,,,  blood-vessels  of  the  hair  papilla;  h,  nbro-vascular 
sheath.    (Cadiat.) 

much,  however,  as  the  posterior  edge  of  the  nail,  from  its  heing  lodged 
in  a  groove  of  the  skin,  cannot  grow  backwards,  on  additions  being  made 
to  it,  so  easily  as  it  can  pass  in  the  opposite  direction,  any  growth  at  its 
hinder  part  pushes  the  whole  forwards.  At  the  same  time  fresh  cells  are 
added  to  its  under  surface,  and  thus  each  portion  of  the  nail  becomes 


348 


HANDBOOK    OF  PHYSIOLOGY, 


gradually  thicker  as  it  moves  to  the  front,  until,  projecting  beyond  the 
surface  of  the  matrix,  it  can  receive  no  fresh  addition  from  beneath,  and 
is  simply  moved  forwards  by  the  growth  at  its  root,  to  be  at  last  worn 
away  or  cut  off. 

Functions  of  the   Skin. 

(1.)  By  means  of  its  toughness,  flexibility,  and  elasticity,  the  skin 
is  eminently  qualified  to  serve  as  the  general  integument  of  the 
body,  for  defending  the  internal  parts  from  external  violence,  and  readily 
yielding  and  adapting  itself  to  their  various  movements  and  changes  of 
position. 

(2.)  The  skin  is  the  chief  organ  of  the  sense  of  touch.  Its  whole 
surface  is  extremely  sensitive;  but  its  tactile  properties  are  due  more  es- 


Fig,  240. — Transverse  section  of  a  hair  and  hair-follicle  made  below  the  opening  of  the  sebace- 
ous gland,  a,  medulla  or  pith  of  the  hair;  b,  fibrous  layer  or  cortex;  c,  cuticle;  d,  Huxley's  layer; 
e,  Henle's  layer  of  internal  root-sheath;  /  andgr,  layers  of  external  root  sheath,  outside  of  g  is  a 
light  layer,  or  "  glassy  membrane,"  which  is  equivalent  to  the  basement  membrane;  b,  fibrous  coat 
of  hair  sac;  i,  vessels.    (Cadiat. ) 

pecially  to  the  abundant  papillae  with  which  it  is  studded.     (See  Chapter 
on  Special  Senses.) 

Although  destined  especially  for  the  sense  of  touch,  the  papillae  are 
not  so  placed  as  to  come  into  direct  contact  with  external  objects;  but 
like  the  rest  of  the  surface  of  the  skin,  are  covered  by  one  or  more  layers 
of  epithelium,  forming  the  cuticle  or  epidermis.  The  papilla?  adhere 
very  intimately  to  the  cuticle,  which  is  thickest  in  the  spaces  between 
them,  but  tolerably  level  on  its  outer  surface:  hence,  when  stripped  off 
from  the  cutis,  as  after  maceration,  its  internal  surface  presents  a  series 
of  pits  and  elevations  corresponding  to  the  papillae  and  their  interspaces 


THE    STRUCTURE    AND    FUNCTIONS   OF   THE    SKIN.  34> 

of  which  it  thus  forms  a  kind  of  mould.  Besides  affording  by  its  imper- 
meability a  check  to  undue  evaporation  from  the  skin,  and  providing  the 
sensitive  cutis  with  a  protecting  investment,  the  cuticle  is  of  service  in 
relation  to  the  sense  of  touch.  For  by  being  thickest  in  the  spaces,  be- 
tween the  papilla?,  and  only  thinly  spread  over  the  summits  of  these  pro- 
cesses, it  may  serve  to  subdivide  the  sentient  surface  of  the  skin  into  a 
number  of  isolated  points,  each  of  which  is  capable  of  receiving  a  dis- 
tinct impression  from  an  external  body.  By  covering  the  papilla?  it  ren- 
ders the  sensation  produced  by  external  bodies  more  obtuse,  and  in  this 
manner  also  is  subservient  to  touch:  for  unless  the  very  sensitive  papilla? 
were  thus  defended,  the  contact  of  substances  would  give  rise  to  pain, 
instead  of  the  ordinary  impressions  of  touch.     This  is  shown  in  the  ex- 


IX 

Fig.  341  .—Vertical  transverse  section  through  a  small  portion  of  the  nail  and  matrix  largely 
magnified.  A,  corium  of  the  nail-bed,  raised  into  ridges  or  laminae  a,  fitting  in  between  correspond- 
ing lamina?  6,  of  the  nail.  B,  Malpighian.  and  C.  horny  layer  of  nail;  d,  deepest  and  vertical  cells; 
e,  upper  flattened  cells  of  Malpighian  layer.     < K<~>lliker. ) 

treme  sensitiveness  and  loss  of  tactile  power  in  a  part  of  the  skin  when 
deprived  of  its  epidermis.  If  the  cuticle  is  very  thick,  however,  as  on 
the  heel,  touch  becomes  imperfect,  or  is  lost. 

(3.)  The  Skin  is  an'organ  of  Secretion,  as  it  possesses  Seba- 
ceous Glands. — The  secretion  of  the  sebaceous  glands  and  hair-follicles 
(for  their  products  cannot  be  separated)  consists  of  cast-off  epithelium 
cells,  with  nuclei  and  granules,  together  with  an  oily  matter,  extractive 
matter,  and  stearin;  in  certain  parts,  also,  it  is  mixed  with  a  peculiar 
odorous  principle,  which  contains  caproic,  butyric,  and  rutic  acids.  It  is. 
perhaps,  nearly  similar  in  composition  to  the  unctuous  coating,  or  remix 
caseosa,  which  is  formed  on  the  body  of  the  foetus  while  in  the  uterus. 
and  which  contains  large  quantities  of  ordinary  fat.     Its  purpose  seems 


350  HANDBOOK    OF    PHYSIOLOGY. 

to  be  that  of  keeping  the  skin  moist  and  supple,  and,  by  its  oily  nature* 
of  both  hindering  the  evaporation  from  the  surface,  and  guarding  the 
skin  from  the  effects  of  the  long-continued  action  of  moisture.  But 
while  it  thus  serves  local  purposes,  its  removal  from  the  body  entitles  it 
to  be  reckoned  among  the  excretions  of  the  skin;  though  the  share  it 
has  in  the  purifying  of  the  blood  cannot  be  discerned. 

(4.)  The  Skin  is  also  an  organ  of  Excretion,  as  it  contains 
Sweat  Glands. — The  fluid  secreted  by  the  sweat-glands  is  usually 
formed  so  gradually  that  the  watery  portion  of  it  escapes  by  evaporation 
as  fast  as  it  reaches  the  surface.  But,  duriug  strong  exercise,  exposure 
to  great  external  warmth,  in  some  diseases,  and  when  evaporation  is  pre- 
vented, the  secretion  becomes  more  sensible,  and  collects  on  the  skin  in 
the  form  of  drops  of  fluid. 

The  perspiration,  as  the  term  is  sometimes  employed  in  physiology, 
includes  all  that  portion  of  the  secretions  and  exudations  from  the  skin 
which  passes  off  by  evaporation  ;  the  sweat  includes  that  which  may  be 
collected  only  in  drops  of  fluid  on  the  surface  of  the  skin.  The  two 
terms  are,  however,  most  often  used  synonymously  ;  and  for  distinction, 
the  former  is  called  insensible  perspiration  ;  the  latter  sensible  perspira- 
tion. The  fluids  are  the  same,  except  that  the  sweat  is  commonly  min- 
gled with  various  substances  lying  on  the  surface  of  the  skin.  The  con- 
tents of  the  sweat  are,  in  part,  matters  capable  of  assuming  the  form  of 
vapor,  such  as  carbonic  acid  and  water,  and  in  part,  other  matters  which 
are  deposited  on  the  skin,  and  mixed  with  the  sebaceous  secretion. 

Table  of  the  Chemical  Composition  of  Sweat. 

Water, , 995 

Solids  : — 

Organic  Acids  (formic,  acetic,  butyric,  propionic,  )        ^ 

caproic,  caprylic), f 

Salts,  chiefly  sodium  chloride,  .         .         .         .         .1.8 
Neutral  fats  and  cholesterin,         .         .         .         .  .7 

Extractives  (including  urea),  with  epithelium,         .1.6  5 

1000 
The  sweat  is  acolorless,  slightly  turbid  fluid,  alkaline,  neutral  or  acid 
in  reaction,  of  a  saltish  taste,  and  peculiar  characteristic  odor. 

Of  the  several  substances  it  contains,  however,  only  the  carbonic  acid 
and  water  need  particular  consideration. 

a.  Watery  vapor. — The  quantity  of  watery  vapor  excreted  from  the 
skin  is  on  an  average  between  \\  and  2  lb.  daily.  This  subject  has  been 
very  carefully  investigated  by  Lavoisier  and  Sequin.  The  latter  chemist 
inclosed  his  body  in  an  air-tight  bag,  with  a  mouth-piece.  The  bag 
being  closed  by  a  strong  band  above,  and  the  mouth-piece  adjusted  and 
gummed  to  the  skin  around  the  mouth,  he  was  weighed,  and  then  re- 


THE    STRUCTURE    AND    FUNCTIONS    OF    THE    SKIN.  351 

mained  quiet  for  several  hours,  after  which  time  he  was  again  weighed. 
The  difference  in  the  two  weights  indicated  the  amount  of  loss  by  pul- 
monary exhalation.  Having  taken  off  the  air-tight  dress,  he  was  imme- 
diately weighed  again,  and  a  fourth  time  after  a  certain  interval.  The 
difference  between  the  two  weights  last  ascertained  gave  the  amount  of 
the  cutaneous  and  pulmonary  exhalation  together  ;  by  subtracting  from 
this  the  loss  by  pulmonary  exhalation  alone,  while  he  was  in  the  air-tight 
dress,  he  ascertained  the  amount  of  cutaneous  transpiration.  During  a 
state  of  rest,  the  average  loss  by  cutaneous  and  pulmonary  exhalation  in 
a  minute  is  eighteen  grains — the  minimum  eleven  grains,  the  maximum 
thirty-two  grains  ;  and  of  the  eighteen  grains,  eleven  pass  off  by  the  skin, 
and  seven  by  the  lungs. 

The  quantity  of  watery  vapor  lost  by  transpiration  is  of  course  in- 
fluenced by  all  external  circumstances  which  affect  the  exhalation  from 
other  evaporating  surfaces,  such  as  the  temperature,  the  hygrometric 
state,  and  the  stillness  of  the  atmosphere.  But,  of  the  variations  to 
which  it  is  subject  under  the  influence  of  these  conditions,  no  calcula- 
tion has  been  exactly  made. 

b.  Carbonic  Acid. — The  quantity  of  carbonic  acid  exhaled  by  the 
skin  on  an  average  is  about  y^-  to  7f7  of  that  furnished  by  the  pulmo- 
nary respiration. 

The  cutaneous  exhalation  is  most  abundant  in  the  lower  classes  of 
animals,  more  particularly  the  naked  Amphibia,  as  frogs  and  toads, 
whose  skin  is  thin  and  moist,  and  readily  permits  an  interchange  of 
gases  between  the  blood  circulating  in  it,  and  the  surrounding  atmo- 
sphere Bischoff  found  that,  after  the  lungs  of  frogs  had  been  tied  and 
cut  out,  about  a  quarter  of  a  cubic  inch  of  carbonic  acid  gas  was  exhaled 
by  the  skin  in  eight  hours.  And  this  quantity  is  very  large,  when  it  is 
remembered  that  a  full-sized  frog  will  generate  only  about  half  a  cubic 
inch  of  carbonic  acid  by  his  lungs  and  skin  together  in  six  hours. 

The  importance  of  the  respiratory  function  of  the  skin,  which  was 
once  thought  to  be  proved  by  the  speedy  death  of  animals  whose  skins, 
after  removal  of  the  hair,  were  covered  with  an  impermeable  varnish, 
has  been  shown  by  further  observations  to  have  no  foundation  in  fact; 
the  immediate  cause  of  death  in  such  cases  being  the  loss  of  temperature. 
A  varnished  animal  is  said  to  have  suffered  no  harm  when  surrounded 
by  cotton  wadding,  and  to  have  died  when  the  wadding  was  removed. 

Influence  of  the  Nervous  System  on  Sweat-Excretion. — Any 

increase  in  the  amount  of  sweat  secreted  is  usually  accompanied  by  dila- 
tation of  the  cutaneous  vessels.  It  is,  however,  probable  that  the  secre- 
tion is  like  the  other  secretions,  e.  g.,  the  saliva,  under  the  direct  action 
of  a  special  nervous  apparatus,  in  that  various  nerves  contain  fibres 
which  act  directly  upon  the  cells  of  the  sweat-glands  in  the  same  way 
that  the  chorda  tympani  contains  fibres  which  act  directly  upon  the  sali- 
vary cells.  The  local  apparatus  is  under  control  of  the  central  nervona 
system — sweat  centres  probably  existing  both  in  the  medulla  and  spinal 


OO'Ji  HANDBOOK    OF    PHYSIOLOGY: 

cord — and  may  be  reflexly  as  well  as  directly  excited.  The  nerve-fibres 
which  induce  sweating  may  act  independently  of  the  vasomotor  fibres, 
whether  vaso-dilator  or  vaso-constrictor.  This  will  explain  the  fact  that 
sweat  occurs  not  only  when  the  skin  is  red,  but  also  when  it  is  pale,  and 
the  cutaneous  circulation  languid,  as  in  the  sweat  which  accompanies 
syncope  or  fainting,  or  which  immediately  precedes  death. 

(5.)  The  Skin  has  a  farther  function,  that  of  Absorption. — 
Absorption  by  the  skin  has  been  already  mentioned,  as  an  instance  in 
which  that  process  is  most  actively  accomplished.  Metallic  preparations 
rubbed  into  the  skin  have  the  same  action  as  when  given  internally, 
only  in  a  less  degree.  Mercury  applied  in  this  manner  exerts  its  specific 
influence  upon  syphilis,  and  excites  salivation  ;  potassio-tartrate  of  anti- 
mony may  excite  vomiting,  or  an  eruption  extending  over  the  whole 
body  ;  and  arsenic  may  produce  poisonous  effects.  Vegetable  matters, 
also,  if  soluble,  or  already  in  solution,  give  rise  to  their  peculiar  effects, 
as  cathartics,  narcotics,  and  the  like,  when  rubbed  into  the  skin.  The 
effect  of  rubbing  is  probably  to  convey  the  particles  of  the  matter  into 
the  orifices  of  the  glands  whence  they  are  more  readily  absorbed  than 
they  would  be  through  the  epidermis.  When  simply  left  in  contact 
with  the  skin,  substances,  unless  in  a  fluid  state,  are  seldom  absorbed. 

It  has  long  been  a  contested  question  whether  the  skin  covered  with  the 
epidermis  has  the  power  of  absorbing  water  ;  and  it  is  a  point  the  more 
difficult  to  determine  because  the  skin  loses  water  by  evaporation.  But, 
from  the  result  of  many  experiments,  it  may  now  be  regarded  as  a  well- 
ascertained  fact  that  such  absorption  really  occurs.  The  absorption  of ' 
water  by  the  surface  of  the  body  may  take  place  in  the  lower  animals 
very  rapidly.  Not  only  frogs,  which  have  a  thin  skin,  but  lizards,  in 
which  the  cuticle  is  thicker  than  in  man,  after  having  lost  weight  by 
being  kept  for  some  time  in  a  dry  atmosphere,  are  found  to  recover  both 
their  weight  and  plumpness  very  rapidly  when  immersed  in  water. 
When  merely  the  tail,  posterior  extremities,  and  posterior  part  of  the 
body  of  the  lizard  are  immersed,  the  water  absorbed  is  distributed 
throughout  the  system.  And  a  like  absorption  through  the  skin,  though 
to  a  less  extent,  may  take  place  also  in  man. 

In  severe  cases  of  dysphagia,  when  not  even  fluids  can  be  taken  into 
the  stomach,  immersion  in  a  bath  of  warm  water  or  of  milk  and  water 
may  assuage  the  thirst;  and  it  has  been  found  in  such  cases  that  the 
weight  of  the  body  is  increased  by  the  immersion.  Sailors  also,  when 
destitute  of  fresh  water,  find  their  urgent  thirst  allayed  by  soaking  their 
clothes  in  salt  water,  and  wearing  them  in  that  state;  but  these  effects 
are  in  part  due  to  the  hindrance  to  the  evaporation  of  water  from  the 
skin. 

(6.)  For  an  account  of  the  important  function  of  the  skin  in  the 
regulation  of  temperature,  see  Chapter  on  Animal  Heat. 


CHAPTER   XII. 

THE    STRUCTURE  AND  FUNCTION  OF  THE  KIDNEYS. 

The  Kidneys  are  two  in  number,  and  are  situated  deeply  in  the 
lumbar  region  of  the  abdomen  on  either  side  of  the  spinal  column  behind 
the  peritoneum.  They  correspond  in  position  to  the  last  two  dorsal  and 
two  upper  lumbar  vertebrae;  the  right  being  slightly  below  the  left  in 
consequence  of  the  position  of  the  liver  on  the  right  side  of  the  abdomen. 
They  are  about  4  inches  long,  2£  inches  broad,  and  1£  inches  thick.  The 
weight  of  each  kidney  is  about  4-^-  oz. 

Structure. — The  kidney  is  covered  by  a  tough  fibrous  capsule,  which 
is  slightly  attached  by  its  inner  surface  to  the  proper  substance  of  the 
organ  by  means  of  very  fine  fibres  of  areolar  tissue  and  minute  blood- 
vessels. From  the  healthy  kidney,  therefore,  it  may  be  easily  torn  off 
without  injury  to  the  subjacent  cortical  portion  of  the  organ.  At  the 
hilus  or  notch  of  the  kidney,  it  becomes  continuous  with  the  external 
coat  of  the  upper  and  dilated  part  of  the  ureter  (Fig.  242). 

On  dividing  the  kidney  into  two  equal  parts  by  a  section  carried 
through  its  long  convex  border  (Fig.  242),  the  main  part  of  its  substance 
is  seen  to  be  composed  of  two  chief  portions,  called  respectively  the  cor- 
tical and  the  medullary  portion,  the  latter  being  also  sometimes  called 
the  pyramidal  portion,  from  the  fact  of  its  being  composed  of  about  a 
dozen  conical  bundles  of  urine  tubes,  each  bundle  being  called  a  pyra- 
mid. The  upper  part  of  the  duct  of  the  organ,  or  the  ureter,  is  dilated 
into  what  is  called  the  pelvis  of  the  kidney;  and  this  again,  after  sepa- 
rating into  two  or  three  principal  divisions,  is  finally  subdivided  into* 
still  smaller  portions,  varying  in  number  from  about  8  to  12,  or  even 
more,  and  called  calyces.  Each  of  these  little  calyces  or  cups,  which 
are  often  arranged  in  a  double  row,  receives  the  pointed  extremity  or 
papilla  of  a  pyramid.  Sometimes,  however,  more  than  one  papilla  is 
received  by  a  calyx. 

The  kidney  is  a  compound  tubular  gland,  and  both  its  cortical  and 
medullary  portions  are  composed  essentially  of  secreting  tubes,  the  tubuli 
uriniferi,  which,  by  one  extremity,  in  the  cortical  portion,  end  com- 
monly in  little  saccules  containing  blood-vessels,  called  Malpighian 
bodies,  and,  by  the  other,  open  through  the  papillae  into  the  pelvis  of  the 
kidney,  and  thus  discharge  the  urine  which  flows  through  them. 


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In  the  pyramids  the  tubes  are  chiefly  straight — dividing  and  diverg- 
ing as  they  ascend  through  these  into  the  cortical  portion  ;  while  in  the 
latter  region  they  spread  out  more  irregularly,  and  become  much 
branched  and  convoluted. 

Tubuli  Uriniferi. — The  tubuli  nriniferi  (Fig.  243)  are  composed  of 
a  nearly  homogeneous  membrane,  and  are  lined  internally  by  epithelium. 
They  vary  considerably  in'  size  in  different  parts  of  their  course,  but  are, 
on  an  average,  about  ^¥  of  an  inch  in  diameter,  and  are  found  to  be 
made  up  of  several  distinct  sections  which  differ  from  one  another  very 
markedly,  both  in  situation  and  structure.  According  to  Klein,  the  fol- 
lowing segments  may  be  made  out:  (1)  The  Malpighian  corpuscle  (Figs. 
244,  245),  composed  of  a  hyaline  membrana  propria,  thickened  by  a 
varying  amount  of  fibrous  tissue,  and  lined  by  flattened  nucleated   epi- 


Fig.  342. 


FiG.  243. 


Fig.  242.— Plan  of  a  longitudinal  section  through  the  pelvis  and  substance  of  the  right  kidney,  K; 
a,  the  cortical  substance;  6.  b,  broad  part  of  the  pyramids  of  Malpighi;  c,  c,'the  divisions  of  the  pel- 
vis named  calyces,  laid  open;  c',  one  of  those  unopened;  d,  summit  of  the  pyramids  of  papillse  pro- 
jecting into  calyces;  e,  e,  section  of  the  narrow  part  of  two  pyramids  near  the  calyces;  p,  pelvis  or 
enlarged  divisions  of  the  ureter  within  the  kidney;  u,  the  ureter;  s,  the  sinus;  h,  the  hilus. 

Fig.  243.— a.  Portion  of  a  secreting  tubule  from  the  cortical  substance  of  the  kidney,  b.  The 
epithelial  or  gland-cells.    X  700  times. 

thelial  plates.  This  capsule  is  the  dilated  extremity  of  the  uriniferous 
tubule,  and  contains  within  it  a  glomerulus  of  convoluted  capillary 
blood-vessels  supported  by  connective  tissue,  and  covered  by  flattened 
epithelial  plates.  The  glomerulus  is  connected  with  an  efferent  and  an 
afferent  vessel.  (2)  The  constricted  neck  of  the  capsule  (Fig.  244,  2), 
lined  in  a  similar  manner,  connects  it  with  (3)  The  Proximal  convoluted 
tubule,  which  forms  several  distinct  curves  and  is  lined  with  short 
columnar  cells,  which  vary  somewhat  in  size.  The  tube  next  passes  al- 
most vertically  downwards,  forming  (4)  The  Spiral  tubule,  which  is  of 
much  the  same  diameter,  and  is  lined  in  the  same  way  as  the  convoluted 
portion.     So  far  the  tube  has  been  contained  in  the  cortex  of  the  kidney; 


STRUCTURE    AND    FUNCTION   OF    THE   KIDNEYS.  355 

it  now  passes  vertically  downward  through  the  most  external  part 
(boundary  layer)  of  the  Malpighian  pyramid  into  the  more  internal  part 
(papillary  layer),  where  it  curves  up  sharply,  forming  altogether  the  (5 
and  6)  Loop  of  Henle,  which  is  a  very  narrow  tube  lined  with  flattened 


FIG.  244. -A  Diagram  of  the  sections  of  uriniferous  tubes.  A.  correx  limited  externally  by  the 
capsule;a,  subcapsular  layer  not  containing  Malpighian  corpuscles;  «'  inner  stratum  of  cortex,  also 
without  Malpighian  corpuscles;  B.  boundary  layer:  C.  Papillary  part  next  the  boundary  layer;  1, 
Bowman's  capsule  of  Malpighian  corpuscle:  2,  neck  of  capsule;  3,  proximal  convoluted  tubule:  4, 
spiral  tubule;  5,  descending  limb  of  Henle's  loop;  6,  the  loop  proper:  7,  thick  part  of  the  ascending 
limb;  8,  spiral  part  of  ascending  limb;  0.  narrow  ascending  limb  in  the  medullary  ray,  10,  the  irreg- 
ular tubule;  11,  the  intercalated  section,  or  the  distal  convoluted  tubule:  12.  the  curved  collecting 
tubule;  13,  the  straight  collecting  tubule  of  the  medullary  ray :  14,  the  collecting  tube  of  the  boundary 
layer;  15,  the  large  collecting  tube  of  the  papillary  part  which,  joining  with  similar  tubes,  forms  the 
duct.    (Klein  and  Noble  Smith,  t 

nucleated  cells.     Passing  vertically  upwards  just  as  the  tube  reaches  the 
boundary  layer   (7),  it  suddenly  enlarges  and  becomes  lined  with  poly- 


356 


HANDBOOK    OF   PHYSIOLOGY. 


hedral  cells.  (8)  About  midway  iu  the  boundary  layer  the  tube  again, 
narrows,  forming  the  ascending  spiral  of  Henle's  loop,  but  is  still  lined, 
with  polyhedral  cells.  At  the  point  where  the  tube  enters  the  cortex  (9) 
the  ascending  limb  narrows,  but  the  diameter  varies  considerably;  here 
and  there  the  cells  are  more  flattened,  but  both  in  this  as  in  (8),  the  cells 
are  in  many  places  very  angular,  branched,  and  imbricated.  It  then 
joins  (10)  the  "  irregular  tubule,"  which  has  a  very  irregular  and  angular 
outline,  and  is  lined  with  angular  and  imbricated  cells.  The  tube  next 
becomes  convoluted  (11),  forming  the  distal  convoluted  tube  or  intercal- 
ated section  of  Sclnveigger-Seidel,  which  is  identical  in  all  respects  with  the 
proximal  convoluted  tube  (12  and  13).     The  curved  and  straight  collect- 


aaaassa 


ipatB   ^^"J-jTTTg^^Binini»i>^T'Tn'"m^~*CTT  j 


Fig.  245.— From  a  vertical  section  through  the  kidney  of  a  dog— the  capsule  of  which  is  supposed 
to  be  on  the  right,  a.  The  capillaries  of  the  Malpighian  corpuscle— viz.,  the  glomerulus,  are  arrang- 
ed in  lobules;  o,  neck  of  capsule;  c,  convoluted  tubes  cut  in  various  directions;  b,  irregular  tubule; 
d,  e,  and  /,  are  straight  tubes  runuing  towards  capsules  forming  a  so-called  medullary  ray,  d,  col- 
lecting tube;  e,  spiral  tube  ;  /,  narrow  section  of  ascending  limb.   X  380.  (Klein  and  Noble  Smith.) 

ing  tubes,  the  former  entering  the  latter  at  right  angles,  and  the  latter 
passing  vertically  downwards,  are  lined  with  polyhedral,  or  spindle- 
shaped,  or  flattened,  or  angular  cells.  The  straight  collecting  tube  now 
enters  the  boundary  layer  (14),  and  passes  on  to  the  papillary  layer, 
and,  joining  with  other  collecting  tubes,  forms  larger  tubes,  which  finally 
open  at  the  apex  of  the  papilla.  These  collecting  tubes  are  lined  with 
transparent  nucleated  columnar  or  cubical  cells  (14,  15). 

The  cells  of  the  tubules,  with  the  exception  of  Henle's  loop  and  all 
parts  of  the  collecting  tubules,  are,  as  a  rule,  possessed  of  the  intra-nu- 


STRUCTURE    AND    FUNCTION    OF    THK    KIDNEYS. 


357 


clear  as  well  as  of  the  intra-cellular  network  of  fibres,  of  which  the  ver- 
tical rods  are  most  conspicuous  parts. 

Heidenhain  observed  that  indigo-sulphate  of  sodium,  and  other  pig- 
ments injected  into  the  jugular  vein  of  an  animal,  were  apparently  ex- 
creted by  the  cells  which  possessed  these  rods,  and  therefore  concluded 
that  the  pigment  passes  through  the  cells,  rods,  and  nucleus  themselves. 
Klein,  however,  believes  that  the  pigment  passes  through  the  intercellu- 
lar substances,  and  not  through  the  cells. 

In  some  places,  it  is  stated  that  a  distinct  membrane  of  flattened 
cells  can  be  made  out  lining  the  lumen  of  the  tubes  {centrotubular  mem- 
brane). 

Blood-supply. — In  connection  with  the  general  distribution  of  blood- 
vessels to  the  kidney,  the  Malpighian  Corpuscles  may  be  further  consid- 


Fig.  246. 


Fig.  247. 


Fig.  246.— Transverse  section  of  a  renal  papilla;  a,  larger  tubes  or  papillary  ducts;  6,  smaller 
tubes  of  Henle;  c,  blood-vessels,  distinguished  by  their  natter  epithelium;  d,  nuclei  of  the  stroma 
(Kolliker).     x  300. 

Fig.  247.  Diagram  showing  the  relation  of  the  Malpighian  body  to  the  uriniferous  ducts  and 
blood-vessels,  a,  one  of  the  interlobular  arteries;  a',  afferent  artery  passing  into  the  glomerulus; 
c,  capsule  of  the  Malpighian  body,  forming  the  termination  of  and  continuous  with  t,  the  uriniferous 
tube;  2,  2,  efferent  vessels  which  subdivide  in  the  plexus,  p,  surrounding  the  tube  and  finally  ter- 
minate in  the  branch  of  the  renal  vein  v  (after  Bowman). 

ered.  They  (Fig.  247)  are  found  only  in  the  cortical  part  of  the  kid- 
ney, and  are  confined  to  the  central  part,  which,  however,  makes  up 
about  seven-eighths  of  the  whole  cortex.  On  a  section  of  the  organ, 
some  of  them  are  just  visible  to  the  naked  eye  as  minute  red  points; 
others  are  too  small  to  be  thus  seen.  Their  average  diameter  is  about 
T£¥  of  an  inch.  Each  of  them  is  composed,  as  we  have  seen  above,  of 
the  dilated  extremity  of  an  uriniferous  tube,  or  Malpighian  capsule, 
which  incloses  a  tuft  of  blood-vessels. 

The  renal  artery  divides  into  several  branches,  which,  passing  in  at 
the  hilus  of  the  kidney,  and  covered  by  a  fine  sheath  of  areolar  tissue 
derived  from  the  capule,  enter  the  substance  of  the  organ  chiefly  in  the 


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HANDBOOK    OF    PHYSIOLOGY. 


intervals  between  the  papillae,  and  at  the  junction  between  the  cortex 
and  the  boundary  layer.  The  main  branches  then  pass  almost  horizon- 
tally, giving  off  branches  upwards  to  the  cortex  and  downwards  to  the 
medulla.  The  former  are  for  the  most  part  straight ;  they  pass  almost 
vertically  to  the  surface  of  the  kidney,  giving  off  laterally  in  all  direc- 
tions longer  or  shorter  branches,  which  ultimately  supply  the  Malpi- 
ghian  bodies. 

The  small  afferent  artery  (Figs.  247  and  249)  which  enters  the  Malpi- 
ghian  corpuscle,  breaks  up  in  the  interior  as  before  mentioned  into  a, 
dense  and  convoluted  and  looped  capillary  plexus,  which  is  ultimately 
gathered  up  again  into  a  single  small  efferent  vessel,  comparable  to  a 
minute  vein,  which  leaves  the  capsule  just  by  the  point  at  which  the 
afferent  artery  enters  it.     On  leaving,  it  does  not  immediately  join  other 


Fig.  248. 


Fig.  249. 


Fig.  248.— Transverse  section  of  a  developing  Malpighian  capsule  and  tuft  (human)  x  300.  From 
a  foetus  at  about  the  fourth  month;  a,  flattened  cells  growing  to  form  the  capsule;  b,  more  rounded 
cells;  continuous  with  the  above,  reflected  round  c,  and  finally  enveloping  it;  c,  mass  of  embryonic 
cells  which  will  later  become  developed  into  blood-vessels.    (W.  Pye.) 

Fig.  249.— Epithelial  elements  of  a  Malpighian  capsule  with  tuft,  with  the  commencement  of  a 
urinary  tubule  showing  the  afferent  and  efferent  vessel ;  a,  layer  of  tesselated  epithelium  forming 
the  capsule;  b,  similar,  but  rather  larger  epithelial  cells,  placed  in  the  walls  of  the  tube;  c,  cells  cov- 
ering the  vessels  of  the  capillary  tuft;  d,  commencement  of  the  tubule,  somewhat  narrower  than 
the  rest  of  it    (W.  Pye.) 


small  veins  as  might  have  been  expected,  but  again  breaking  up  into  a  net- 
work of  capillary  vessels,  is  distributed  on  the  exterior  of  the  tubule, 
from  whose  dilated  end  it  had  just  emerged.  After  this  second  break- 
ing up  it  is  finally  collected  into  a  small  vein,  which,  by  union  with 
others  like  it,  helps  to  form  the  radicles  of  the  renal  vein. 

Thus,  in  the  kidney,  the  blood  entering  by  the  renal  artery,  traverses 
tivo  sets  of  capillaries  before  emerging  by  the  renal  vein,  an  arrangement 
which  may  be  compared  to  the  portal  system  in  miniature. 

The  tuft  of  vessels  in  the  course  of  development  is,  as  it  were,  thrust 


STRUCTURE   AND    FUNCTION    OF   THE   KIDNEYS.  350 

into  the  dilated  extremity  of  the  urinary  tubule,  which  finally  completely 
invests  it  just  as  the  pleura  invests  the  lungs  or  the  tunica  vaginalis 
the  testicle.  Thus  the  Malpighian  capsule  is  lined  by  a  parietal  layer  of 
squamous  cells  and  a  visceral  or  reflected  layer  immediately  covering  the 
vascular  tuft  (Fig.  245),  and  sometimes  dipping  down  into  its  inter- 
stices. This  reflected  layer  of  epithelium  is  readily  seen  in  young  sub- 
jects, but  cannot  always  be  demonstrated  in  the  adult.  (See  Figs.  248 
and  249.) 

The  vessels  which  enter  the  medullary  layer  break  up  into  small  ar- 
terioles, which  pass  through  the  boundary  layer,  and  proceed  in  a 
straight  course  between  the  tubules  of  the  papillary  layer,  giving  off  on 
their  way  branches,  which  form  a  fine  arterial  meshwork  around  the 
tubes,  and  ending  in  a  similar  plexus  from  which  the  venous  radicles 
arise. 

Besides  the  small  afferent  arteries  of  the  Malpighian  bodies,  there 
are,  of  course,  others  which  are  distributed  in  the  ordinary  manner,  for 
the  nutrition  of  the  different  parts  of  the  organ;  and  in  the  pyramids 
between  the  tubes,  there  are  numerous  straight  vessels,  the  vasa  recta, 
some  of  which  are  branches  of  vasa  efferentia  from  Malpighian  bodies, 
and  therefore  comparable  to  the  venous  plexus  around  the  tubules  in  the 
cortical  portion,  while  others  arise  directly  as  small  branches  of  the  renal 
arteries. 

Between  the  tubes,  vessels,  etc.,  which  make  up  the  substance  of  the 
kidney,  there  exists,  in  small  quantity,  a  fine  matrix  of  areolar  tissue. 

Nerves. — The  nerves  of  the  kidney  are  derived  from  the  renal 
plexus. 

The  Ureters. — The  duct  of  each  kidney,  or  ureter,  is  a  tube  about 
the  size  of  a  goose-quill,  and  from  twelve  to  sixteen  inches  in  length, 
which,  continuous  above  with  the  pelvis  of  the  kidney,  ends  below  by 
perforating  obliquely  the  walls  of  the  bladder,  and  opening  on  its  inter- 
nal surface. 

Structure. — It  is  constructed  of  three  principal  coats  (a)  an  outer, 
tough,  fibrous  and  elastic  coat;  (b)  a  middle  muscular  coat,  of  which 
the  fibres  are  unstriped,  and  arranged  in  three  layers — the  fibres  of  the 
central  layer  being  circular,  and  those  of  the  other  two  longitudinal  in 
direction;  and  (c)  an  internal  mucous  lining  continuous  with  that  of 
the  pelvis  of  the  kidney  above,  and  of  the  urinary  bladder  below.  The 
epithelium  of  all  these  parts  (Fig.  250)  is  alike  stratified  and  of  a  some- 
what peculiar  form;  the  cells  on  the  free  surface  of  the  mucous  mem- 
brane being  usually  spheroidal  or  polyhedral  with  one  or  more  spherical 
or  oval  nuclei;  while  beneath  these  are  pear-shaped  cells,  of  which  the 
broad  ends  are  directed  towards  the  free  surface,  fitting  in  beneath  the 
cells  of  the  first  row,  and  the  apices  are  prolonged  into  processes  of  vari- 


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HANDBOOK    OF    PHYSIOLOGY. 


ous  lengths,  among  which,  again,  the  deepest  cells  of  the  epithelium  are 
found  spheroidal,  irregularly  oval,  spindle-shaped  or  conical. 

The  Urinary  Bladder. — The  urinary  bladder,  which  forms  a  re- 
ceptacle for  the  temporary  lodgment  of  the  urine  in  the  intervals  of  its 
expulsion  from  the  body,  is  more  or  less  pyriform,  its  widest  part,  which 
is  situate  above  and  behind,  being  termed  the  fundus:  and  the  narrow 
constricted  portion  in  front  and  below,  by  which  it  becomes  continuous 
with  the  urethra,  being  called  its  cervix  or  neck. 

Structure. — It  is  constructed  of  four  principal  coats — serous,  mus- 
cular, areolar  or  submucous,  and  mucous.  (a)  The  serous  coat,  which 
covers  only  the  posterior  and  upper  half  of  the  bladder,  has  the  same 
structure  as  that  of  the  peritoneum,  with  which  it  is  continuous,  (b)  The 
fibres  of  the  muscular  coat,  which  are  unstriped,  are  arranged  in  three 
principal  layers,  of  which  the  external  and  internal  have  a  general  lon- 
gitudinal, and  the  middle  layer  a  circular  direction.     The  latter  are  es- 


Fig.  250. — Epithelium  of  the  bladder;  a,  one  of  the  cells  of  the  first  row;  b,  a  cell  of  the  second 
row;  c,  cells  in  situ,  of  first,  second,  and  deepest  layers.    (Obersteiner.) 


pecially  developed  around  the  cervix  of  the  organ,  and  are  described  as 
forming  a  sphincter  vesicce.  The  muscular  fibres  of  the  bladder,  like 
those  of  the  stomach,  are  arranged  not  in  simple  circles,  but  in  figure- 
of-8  loops,  (c)  The  areolar  or  submucous  coat  is  constructed  of  con- 
nective tissue  with  a  large  proportion  of  elastic  fibres,  (d)  The  mucous 
membrane,  which  is  rugose  in  the  contracted  state  of  the  organ,  does  not 
differ  in  essential  structure  from  mucous  membranes  in  general.  Its 
epithelium  is  stratified  and  closely  resembles  that  of  the  pelvis  of  the 
kidney  and  the  ureter  (Fig.  250). 

The  mucous  membrane  is  provided  with  mucous  glands,  which  are 
more  numerous  near  the  neck  of  the  bladder. 

The  bladder  is  well  provided  with  blood-  and  lymph-vessels,  and  with 
nerves.  The  latter  are  branches  from  the  sacral  plexus  (spinal)  and 
hypogastric  plexus  (sympathetic).  A  few  ganglion-cells  are  found,  here 
and  there,  in  the  course  of  the  nerve-fibres. 


STRUCTURE    AND    FUNCTION    OF    THE    KIDNEYS. 


361 


The  Urine. 

Physical  Properties. — Healthy  urine  is  a  perfectly  transparent, 
amber-colored  liquid,  with  a  peculiar,  but  not  disagreeable  odor,  a  bit- 
terish taste,  and  a  slight  acid  reaction.  Its  specific  gravity  varies  from 
1015  to  1025.  On  standing  for  a  short  time,  a  little  mucus  appears  in 
it  as  a  flocculent  cloud. 

Chemical  Composition. — The  urine  consists  of  water,  holding  in  so- 
lution certain  organic  and  saline  matters  as  its  ordinary  constituents, 
and  occasionally  various  other  matters;  some  of  the  latter  are  indications 
of  diseased  states  of  the  system,  and  others  are  derived  from  unusual  ar- 
ticles of  food  or  drugs  taken  into  the  stomach. 


Table  of  the  Chemical  Composition  of  the  Urine. 


Water, 

Solids — 

Urea, 

Other  nitrogenous  crystalline  bodies — 
Uric  acid,  principally  in  the  form  of 
alkaline  Urates,  a  trace  only  free. 
Kreatinin,  Xanthin,  Hypoxanthin. 
Hippuric  acid,  Lencin,  Tyrosin,  Tau- 
rin,    Cystin,    etc.,     all    in    small 
amounts  and  not  constant. 
Mucus  and  Pigment. 

Salts:— 

Inorganic — 

Principally   Sulphates,    Phosphates,  ' 
and    Chlorides    of    Sodium,    and 
Potassium,    with    Phosphates    of 
Magnesium  and  Calcium,  traces  of 
Silicates  of  and  Chlorides. 

Organic — 

Lactates,  Hippu  rates,  Acetates,  and 
Formates,  which  only  appear  occa- 
sionally. 
Sugar,      ........ 

Gases  (nitrogen  and  carbonic  acid  principally). 


967 


14.230 


10.635 


8.135 


—    33 

a  trace  sometimes. 


1000 


Reaction. — The  normal  reaction  of  the  urine  is  slightly  acid.  This 
acidity  is  due  to  acid  phosphate  of  sodium,  and  is  less  marked  soon  after 
meals.  The  urine  contains  no  appreciable  amount  of  free  acid,  as  it 
gives  no  precipitate  of  sulphur  with  sodium  hyposulphite.  After  stand- 
ing for  some  time  the  acidity  increases  from  a  kind  of  acid  fermentation. 
due  in  all  probability  to  the  presence  of  mucus  and  fungi,  and  acid 


362  HANDBOOK    OF   PHYSIOLOGY. 

urates  or  free  uric  acid  is  deposited.  After  a  time,  varying  in  length  ac- 
cording to  the  temperature,  the  reaction  becomes  strongly  alkaline  from 
the  change  of  urea  into  ammonium  carbonate,  due  to  the  presence  of 
one  or  more  specific  micro-organisms  (micrococcus  ureas).  The  urea 
takes  up  two  molecules  of  water — a  strong  ammoniacal  and  foetid  odor 
appears,  and  deposits  of  triple  phosphates  and  alkaline  urates  take  place. 
This  does  not  occur  unless  the  urine  is  freely  exposed  to  the  air,  or,  at 
least,  until  air  has  had  access  to  it. 

Reaction  of  Urine  in  different  classes  of  Animals. — In  most  herbivo- 
rous animals  the  urine  is  alkaline  and  turbid.  The  difference  depends, 
not  on  any  peculiarity  in  the  mode  of  secretion,  but  on  the  differences 
in  the  food  on  which  the  two  classes  subsist;  for  when  carnivorous  ani- 
mals, such  as  dogs,  are  restricted  to  a  vegetable  diet,  their  urine  becomes 
pale,  turbid,  and  alkaline,  like  that  of  an  herbivorous  animal,  but  re- 
sumes its  former  acidity  on  the  return  to  an  animal  diet  ;  while  the 
urine  voided  by  herbivorous  animals,  e.g.,  rabbits,  fed  for  some  time  ex- 
clusively upon  animal  substances,  presents  the  acid  reaction  and  other 
qualities  of  the  urine  of  Carnivora,  its  ordinary  alkalinity  being  restored 
only  on  the  substitution  of  a  vegetable  for  the  animal  diet.  Human 
urine  is  not  usually  rendered  alkaline  by  vegetable  diet,  but  it  becomes 
so  after  the  free  use  of  alkaline  medicines,  or  of  the  alkaline  salts  with 
carbonic  or  vegetable  acids;  for  these  latter  are  changed  into  carbonates 
previous  to  elimination  by  the  kidneys. 

Average  daily  quantity  of  the  chief  constituents  of  the  Urine 

{by  healthy  male  adults). 

Water,         ......  52.       fluid  ounces. 

Urea, 512.4    grains. 

Uric  acid,    ......  8.5         " 

Hippuric  acid,  uncertain,     probably  10  to  15.  " 

Sulphuric  acid,        .         .         .         .  31.11 

Phosphoric  acid,  ....  45.  " 

Potassium,  Sodium,  and  Ammonium  )         090  nt       <e 

Chlorides  and  free  Chlorine,     .        J 
Lime,       ......  3.5       " 

Magnesia, 3.  " 

Mucus, 7.  " 

'Kreatinin,  "1 

I  Pigment, 

1  Xanthin,  I  -.~a 

k  Hypoxanthin, 
Eesinous  matter, 
etc., 


Extractives, 


Variations  in  the  Quantity  of  the  Constituents. — From  the 
proportions  given  in  the  above  table,  most  of  the  constituents  are,  even 
in  health,  liable  to  variations.  The  variations  of  the  water  in  diffeient 
seasons,  and  according  to  the  quantity  of  drink  and  exercise,  have  al- 
ready been  mentioned.     The  water  of  the  urine  is  also  liable  to  be  influ- 


STRUCTURE   AND    FUNCTION    OF    THE    KIDNEYS.  3<j5 

enced  by  the  condition  of  the  nervous  system,  being  sometimes  greatly 
increased,  e.  g.,  in  hysteria,  and  in  some  other  nervous  affections;  and 
at  other  times  diminished.  In  some  diseases  it  is  enormously  increased; 
and  its  increase  may  be  either  attended  with  an  augmented  quantity  of 
solid  matter,  as  in  ordinary  diabetes,  or  may  be  nearly  the  sole  change, 
as  in  the  affection  termed  diabetes  insipidus.  In  other  diseases,  e.  g., 
the  various  forms  of  albuminuria,  the  quantity  may  be  considerably  di- 
minished. A  febrile  condition  almost  always  diminishes  the  quantity  of 
water  ;  and  a  like  diminution  is  caused  by  any  affection  which  draws  off 
a  large  quantity  of  fluid  from  the  body  through  any  other  channel  than 
that  of  the  kidneys,  e.  g.,  the  bowels  or  the  skin. 

Method  of  estimating  the  Solids. — A  useful  rule  for  approximately 
estimating  the  total  solids  in  any  given  specimen  of  healthy  urine  is  to 
multiply  the  last  two  figures  representing  the  specific  gravity  by  2.33. 
Thus  in  urine  of  sp.  gr.  1025,  2.33  x  25  =  58.25  grains  of  solids,  are  con- 
tained in  1000  grains  of  the  urine.  In  using  this  method  it  must  be 
remembered  that  the  limits  of  error  are  much  wider  in  diseased  than  in 
healthy  urine. 

Variations  in  the  Specific  Gravity. — The  average  specific  gravity 
of  the  human  urine  is  about  1020.  The  relative  quantity  of  water  and 
of  solid  constituents  of  which  it  is  composed  is  materially  influenced  by 
the  condition  and  occupation  of  the  body  during  the  time  at  which  it  is 
secreted;  by  the  length  of  time  which  has  elapsed  since  the  last  meal; 
and  by  several  other  accidental  cii'cumstances.  The  existence  of  these 
causes  of  difference  in  the  composition  of  the  urine  has  led  to  the  secre- 
tion being  described  under  the  three  heads  of  Urina  sanguinis,  Urina 
potus,  and  Urina  cibi.  The  first  of  these  names  signifies  the  urine,  or 
that  part  of  it  which  is  secreted  from  the  blood  at  times  in  which  neither 
food  nor  drink  has  been  recently  taken,  and  is  applied  especially  to  the 
urine  which  is  evacuated  in  the  morning  before  breakfast.  The  terms 
urina  potus  indicates  the  urine  secreted  shortly  after  the  introduction  of 
any  considerable  quantity  of  fluid  into  the  body;  and  the  urina  cibi,  the 
portions  secreted  during  the  period  immediately  succeeding  a  meal  of 
solid  food.  The  last  kind  contains  a  larger  quantity  of  solid  matter  than 
either  of  the  others;  the  first  or  second,  being  largely  diluted  with  water, 
possesses  a  comparatively  low  specific  gravity.  Of  these  three  kinds  the 
morning  urine  is  the  best  calculated  for  analysis  in  health,  since  it  rep- 
resents the  simple  secretion  unmixed  with  the  elements  of  food  or  drink; 
if  it  be  not  used,  the  whole  of  the  urine  passed  during  a  period  of 
twenty-four  hours  should  be  taken.  Tiie  specific  gravity  of  the  urine 
may  thus,  consistently  with  health,  range  widely  on  both  sides  of  the 
usual  average.  It  may  vary  from  1015  in  the  winter,  to  1025  in  the 
summer  ;  but  variations  of  diet  and  exercise,  and  many  other  circum- 
stances, may  make  even  greater  differences  than  these.     In  disease,  the 


561 


HANDBOOK   OF   PHYSIOLOGY. 


variation  may  be  greater;  sometimes  descending,  in  albuminuria,  to 
1004,  and  frequently  ascending  in  diabetes,  when  the  urine  is  loaded 
with  sugar,  to  1050,  or  even  to  1060. 

Quantity. — The  total  quantity  of  urine  passed  in  twenty-four  hours 
is  affected  by  numerous  circumstances.  On  taking  the  mean  of  many 
observations  by  several  experimenters,  the  average  quantity  voided  in 
twenty-four  hours  by  healthy  male  adults  from  20  to  40  years  of  age  has 
been  found  to  amount  to  about  52£  fluid  ounces  (11  to  2  litres). 

Abnormal  Constituents. — In  disease,  or  after  the  ingestion  of  special 
foods,  various  abnormal  substances  occur  in  urine,  of  which  the  follow- 
ing maybe  mentioned— Serum-albumin,  Globulin,  Ferments  (appar- 
ently present  in  health  also),  Peptone,  Blood,  Sugar,  Bile  acids  and 
pigments,  Casts,  Fats,  various  Salts  taken  as  medicine,  Micro-or- 
ganisms of  various  kinds,  and  other  matters. 

The  Solids  of  the  Urine. 

(1.)  Urea. — (CH4N20.) — Urea  is  the  principal  solid  constituent  of 
the  urine,  forming  nearly  one-half  of  the  whole  quantity  of  solid  matter. 
It  is  also  the  most  important  ingredient,  since  it  is  the  chief   substance 


Fig.  251.— Crystals  of  Urea. 

oy  which  the  nitrogen  of  decomposed  tissue  and  of  any  superfluous  food 
is  excreted  from  the  body.  For  its  removal,  the  secretion  of  urine  seems 
especially  provided;  and  by  its  retention  in  the  blood  the  most  pernicious 
effects  are  produced. 

Properties. — Urea,  like  the  other  solid  constituents  of  the  urine,  ex- 
ists in  a  state  of  solution.  When  in  the  solid  state,  it  appears  in  the 
form  of  delicate  silvery  acicular  crystals,  which,  under  the  microscope, 
appear  as  four-sided  prisms  (Fig.  251).  It  may  be  obtained  in  this  state 
by  evaporating  urine  carefully  to  the  consistence  of  honey,  acting  on  the 
inspissated  mass  with  four  parts  of  alcohol,  then  evaporating  the  alco- 
holic solution  to  dryness,  and  purifying  the  residue  by  repeated  solution 
in  water  or  in  alcohol,  and  finally  allowing  it  to  crystallize.     It  readily 


STRUCTURE    AND    FUNCTION    OF    THE    KIDNEYS.  385 

combines  with  some  acids,  like  a  weak  base;  and  may  thus  be  conveni- 
ently procured  in  the  form  of  crystals  of  nitrate  or  oxalate  of  urea 
(Figs.  252  and  253). 

Urea  is  colorless  when  pure;  when  impure  it  may  be  yellow  or  brown: 
it  is  without  smell,  and  of  a  cooling  nitre-like  taste;  it  has  neither  an 
acid  nor  an  alkaline  reaction,  and  deliquesces  in  a  moist  and  warm  at- 
mosphere. At  59°  F.  (15°  C.)  it  requires  for  its  solution  less  than  its 
own  weight  of  water;  it  is  dissolved  in  all  proportions  by  boiling  water; 
but  it  requires  five  times  its  weight  of  cold  alcohol  for  its  solution.  It 
is  insoluble  in  ether.  At  248°  F.  (120°  C.)  it  melts  without  undergoing 
decomposition;  at  a  still  higher  temperature  ebullition  takes  place,  and 
carbonate  of  ammonium  sublimes;  the  melting  mass  gradually  acquires 
a  pulpy  consistence;  and  if  the  heat  is  carefully  regulated,  leaves  a  gray- 
white  powder,  cyanic  acid. 

Chemical  Nature. — Urea  is  isomeric  with  ammonium  cyanate,  NH4, 
CNO.  It  was  first  of  all  artificially  prepared  from  that  substance.  It  is  usu- 


Fiq.  252.— Crystals  of  Urea  nitrate.  Fig.  253. — Crystals  of  Urea  oxalate. 

ally  considered  to  be  a  diamide  of  carbonic  acid,  in  other  words,  carbonic 
acid,  CO  (OH)'3,  with  two  of  hydroxyl,  (OH)'2  replaced  by  two  of  amido- 
gen  (NHJ'3.  It  may  also  be  written  as  if  it  were  a  monamide  of  carbamic 
acid  (COOHNHJ,  thusCONH2.  NHa;  one  of  amidogen  JSTH9  in  the  latter 
replacing  one  of  hydroxyl  in  the  former.  On  heating,  urea  is  converted 
into  ammonium  carbonate  and  cyanic  acid.  A  similar  decomposition  of 
the  urea  with  development  of  ammonium  carbonate  ensues  spontaneously 
when  urine  is  kept  for  some  days  after  being  voided,  and  explains  the  am- 
moniacal  odor  then  evolved.  The  urea  is  sometimes  decomposed  before 
it  leaves  the  bladder,  when  the  mucous  membrane  is  diseased,  and  the 
mucus  secreted  by  it  is  both  more  abundant,  and,  probably,  more  prone 
to  act  as  a  ferment;  although  the  decomposition  does  not  often  occur 
unless  atmospheric  germs  have  had  access  to  the  urine. 

Variations  in  Quantity  excreted.— The  quantity  of  urea  excreted  is, 
like  that  of  the  urine  itself,  subject  to  considerable  variation.  For  a 
healthy  adult  500  grains  (about  32.5  grms.)  per  diem  may  be  taken  as 
rather  a  high  average.  Its  percentage  in  healthy  urine  is  1.5  to  2.5.  Its 
amount  is  materially  influenced  by  diet,  being  greater  when  animal  food 


366  HANDBOOK    OF   PHYSIOLOGY. 

is  exclusively  used,  less  when  the  diet  is  mixed,  and  least  of  all  with  a 
vegetable  diet.  As  a  rule,  men  excrete  a  larger  quantity  than  women, 
and  persons  in  the  middle  periods  of  life  a  larger  quantity  than  infants 
or  old  people.  The  quantity  of  urea  excreted  by  children,  relatively  to 
their  body-weight,  is  much  greater  than  by  adults.  Thus  the  quantity 
of  urea  excreted  per  kilogram  of  weight  was,  in  a  child,  0.8  grm.  ;  in 
an  adult  only  0.4  grm.  Eegarded  in  this  way,  the  excretion  of  carbonic 
acid  gives  similar  results,  the  proportions  in  the  child  and  adult  being 
as  82  •  34. 

The  quantity  of  urea  does  not  necessarily  increase  and  decrease  with 
that  of  the  urine,  though  on  the  whole  it  would  seem  that  whenever  the 
amount  of  urine  is  much  augmented,  the  quantity  of  urea  also  is  usually 
increased;  and  it  appears  that  the  quantity  of  urea,  as  of  urine,  may  be 
especially  increased  by  drinking  large  quantities  of  water.  In  various 
diseases  the  quantity  is  reduced  considerably  below  the  healthy  standard, 
while  in  other  affections  it  is  above  it. 

Quantitative  Estimation. — There  are  two  chief  methods  of  estimating 
the  amount  of  urea  in  the  urine.  (1.)  By  decomposing  it  by  means  of 
an  alkaline  solution  of  sodium  hypobromite,  or  hypochlorite,  and  calcu- 
lating the  amount  in  a  measured  quantity,  by  collecting  and  measuring 
the  amount  of  nitrogen  evolved  under  such  circumstances.  Urea  con- 
tains nearly  half  its  weight  of  nitrogen,  hence  the  amount  of  the  gas 
collected  may  be  taken  as  a  measure  of  the  urea  decomposed.  The  per- 
centage of  urea  can  of  course  be  readily  calculated  from  the  volume  of 
nitrogen  evolved  from  a  measured  quantity  of  the  urine,  but  this  calcu- 
lation is  avoided  by  graduating  the  tube  in  which  the  nitrogen  is  collected 
with  numbers  which  indicate  the  corresponding  percentage  of  urea.  The 
reaction  is  CON2H4  +  3NaBrO  +  2NaHO=3NaBr  +  3H20  +  Na2C03  +  N3. 
(2.)  By  precipitating  the  urea  by  adding  to  a  given  amount  of  urine, 
freed  from  sulphates  and  phosphates,  a  standard  solution  of  mercuric 
nitrate  from  a  burette,  until  the  whole  of  it  has  been  thrown  down  in  an 
insoluble  form;  then  reading  off  the  exact  amount  of  the  mercuric  ni- 
trate solution,  which  it  was  necessary  to  use.  As  the  amount  of  urea 
which  each  cubic  centimetre  of  the  standard  solution  will  precipitate  is 
previously  known,  it  is  easy  to  calculate  the  amount  in  the  sample  of 
urine  taken.  The  precipitate  which  is  formed  is  generally  said  to  be 
composed  of  mercuric  oxide  and  urea.  Some,  however,  consider  that  it 
is  a  mixture  of  mercuric  nitrate  itself  and  urea. 

(2.) 'Uric  Acid  (C5H4N403). — Uric  or  lithic  acid  is  rarely  absent  from 
the  urine  of  man  or  animals,  though  in  the  feline  tribe  it  seems  to  be 
sometimes  entirely  replaced  by  urea. 

Properties. — Uric  acid  when  pure  is  colorless,  but  when  deposited 
from  the  urine  is  yellowish-brown.  It  crystallizes  in  various  forms  (Fig. 
254).     It  is  odorless  and  tasteless.     It  is  slightly  soluble  in  cold  water, 


STRUCTURE    AND    FUNCTION   OF    THE    KIDNEYS.  S&J 

and  a  little  more  so  in  hot  water,  quite  insoluble  in  alcohol  and  ether. 
It  dissolves  freely  in  solution  of  the  alkaline  carbonates  and  other  salts. 

The  proportionate  quantity  of  uric  acid  varies  considerably  in  differ- 
ent animals.  In  man,  and  Mammalia  generally,  especially  the  Herbi- 
vora,  it  is  comparatively  small.  In  the  whole  tribe  of  birds,  and  of 
serpents,  on  the  other  hand,  the  quantity  is  very  large,  greatly  exceeding 
that  of  the  urea.  In  the  urine  of  granivorous  birds,  indeed,  urea  is 
rarely  if  ever  found,  its  place  being  entirely  supplied  by  uric  acid. 

Variations  in  Quantity. — The  quantity  of  uric  acid,  like  that  of 
urea,  in  human  urine,  is  increased  by  the  use  of  animal  food,  and  de- 
creased by  the  use  of  food  free  from  nitrogen,  or  by  an  exclusively  vege- 
table diet.  In  most  febrile  diseases,  and  in  plethora,  it  is  formed  in 
unnaturally  large  quantities;  and  in  gout  it  is  deposited  in  and  around 
joints,  in  the  form  of  urate  of  soda,  of  which  the  so-called  chalk-stones 
of  this  disease  are  principally  composed.  The  average  amount  secreted 
in  twenty-four  hours  is  8.5  grains  (rather  more  than  half  a  gramme). 

Condition  in  the  Urine. — The  condition  in  which  uric  acid  exists  in 
solution  in  the  urine  has  formed  the  subject  of  some  discussion,  because 
of  its  difficult  solubility  in  water.  The  uric  acid  exists  as  urate  of  soda, 
produced  by  the  uric  acid  as  soon  as  it  it  is  formed  combining  with  part 
of  the  base  of  the  alkaline  sodium  phosphate  of  the  blood.  Hippuric 
acid,  which  exists  in  human  urine  also,  acts  upon  the  alkaline  phosphate 
in  the  same  way,  and  increases  still  more  the  quantity  of  acid  phosphate, 
on  the  presence  of  which  it  is  probable  that  a  part  of  the  natural  acidity 
of  the  urine  depends.  It  is  scarcely  possible  to  say  whether  the  union 
of  uric  acid  with  the  base  sodium,  and  probably  ammonium,  takes  jjlace 
in  the  blood,  or  in  the  act  of  secretion  in  the  kidney:  the  latter  is  more 
likely;  but  the  quantity  of  either  uric  acid  or  urates  in  the  blood  is  proba- 
bly too  small  to  allow  of  this  question  being  solved. 

Owing  to  its  existence  in  combination  in  healthy  urine,  uric  acid  for 
examination  must  generally  be  precipitated  from  its  bases  by  a  stronger 
acid.  Frequently,  however,  when  excreted  in  excess,  it  is  deposited  in 
a  crystalline  form  (Fig.  254),  mixed  with  large  quantities  of  ammonium 
or  sodium  urate.  In  such  cases  it  may  be  procured  for  microscopic  ex- 
amination by  gently  warming  the  portion  of  urine  containing  the  sedi- 
ment; this  dissolves  urate  of  ammonium  and  sodium,  while  the  compara- 
tively insoluble  crystals  of  uric  acid  subside  to  the  bottom. 

The  most  common  form  in  which  uric  acid  is  deposited  in  urine,  is 
that  of  a  brownish  or  yellowish  powdery  substance,  consisting  of  granules 
of  ammonium  or  sodium  urate.  When  deposited  in  crystals,  it  is  most 
frequently  in  rhombic  or  diamond-shaped  lamina?,  but  other  forms  are 
not  uncommon  (Fig.  254).  When  deposited  from  urine,  the  crystals  are 
generally  more  or  less  deeply  colored,  from  being  combined  with  the 
coloring  principles  of  the  urine. 


36S 


HANDBOOK    OF    PHYSIOLOGY. 


Tests. — There  are  two  chief  tests  for  uric  acid  besides  the  microscopic 
evidence  of  its  crystalline  structure:  (1)  The  Murexide  test,  which  con- 
sists of  evaporating  to  dryness  a  mixture  of  strong  nitric  acid  and  uric 
acid  in  a  water  bath.  This  leaves  a  yellowish-red  residue  of  Alloxan 
(C4H„N204)  and  urea,  and  on  addition  of  ammonium  hydrate,  a  beautiful 
purple  color  (ammonium  purpurate,  C8H4  (NH4)N506),  deepened  on 
addition  of  caustic  potash,  takes  place.  (2)  Schiff's  test  consists  of  dis- 
solving the  uric  acid  in  sodium  carbonate  solution,  and  of  dropping  some 
of  it  on  a  filter  paper  moistened  with  silver  nitrate.  A  black  spot 
appears,  which  corresponds  to  the  reduction  of  silver  by  the  uric  acid. 

(3)  Hippuric  Acid  (C9H9NOs)  has  long  been  known  to  exist  in  the 
urine  of  herbivorous  animals  in  combination  with  soda.  It  also  exists 
naturally  in  the  urine  of  man,  in  a  quantity  equal  or  rather  exceeding 
that  of  the  uric  acid. 

The  quantity  of  hippuric  acid  excreted  is  increased  by  a  vegetable 


Fig.  254. 


Fig   S "5 


Fig.  254.— Various  forms  of  uric  acid  crystals. 
Fig.  255.— Crystals  of  hippuric  acid. 

diet.  It  appears  to  be  formed  in  the  body  from  benzoic  acid  or  from 
some  allied  substance.  The  benzoic  acid  unites  with  glycin,  probably  in 
the  kidneys,  and  hippuric  acid  and  water  are  formed  thus,  C7H602  (Ben- 
zoic acid)  +  C2H5N02  (Glycin)  =  C9H9N03  (Hippuric  acid)  +  HaO 
(water).     It  may  be  decomposed  by  acids  into  benzoic  acid  and  glycin. 

Properties. — It  is  a  colorless  and  odorless  substance  of  bitter  taste, 
crystallizes  in  semi-transparent  rhombic  prisms  (Fig.  255).  It  is  more 
soluble  in  cold  water  than  uric  acid,  and  much  more  soluble  in  hot 
water.     It  is  soluble  in  alcohol. 

(4)  Pigments. — The  pigments  of  the  urine  are  the  following: — 1. 
TJroclirome,  a  yellow  coloring  matter,  giving  no  absorption  band;  of 
which  but  little  is  known.  Urine  owes  its  yellow  color  mainly  to  the 
presence  of  this  body.  2.  Urobilin,  an  orange  pigment,  of  which  traces 
may  be  found  in  nearly  all  urines,  and  which  is  especially  abundant  in 
the  urines  passed  by  febrile  patients.     It  is  characterized  by  a  well- 


STRUCTURE    AND    FUNCTION    OF    THE   KIDNEYS.  369 

marked  spectroscopic  absorption  band  at  the  junction  of  green  and 
blue,  best  seen  in  acid  solutions;  and  by  giving  a  green  fluorescence 
when  excess  of  ammonia  with  a  little  chloride  of  zinc  is  added  to  it. 
The  very  vexed  question  of  the  relation  of  the  pigments  of  urine  to  bile 
pigments  turns  largely  upon  the  spectroscopic  appearances  of  urobilin; 
for  orange-colored  solutions  having  the  same  absorption  band  as  urobilin 
may  be  prepared  from  bile  pigments  in  two  different  ways — i.,  by  reduc- 
tion with  sodium  amalgam — Hiidrobilinibia  (Maly);  ii.,  by  oxidation 
with  nitric  acid — Choletelin  (Jaffe),  and  both  these  bile  derivatives  give 
a  fluorescence  with  ammonia  and  a  drop  of  chloride  of  zinc.  It  is  not 
satisfactorily  settled  which  of  these,  if  either,  is  the  same  as  urobilin  of 
urine.  It  is  worth  noting  that  choletelin  may  be  oxidized  a  stage  fur- 
ther; it  then  loses  its  absorption  band,  remaining  however  of  a  yellow 
color.  It  is  very  possible  that  the  urochrome  of  normal  urine  may  be 
this  oxidized  choletelin,  and  that  the  presence  of  the  absorption  band  of 
urobilin  in  urines  may  mean  that  some  of  the  pigment  is  in  the  stage  of 
choletelin;  i.e.,  that  its  oxidation  is  not  quite  completed. 

Those  who  believe  urobilin  to  be  identical  with  hydrobilirubin  sup- 
pose that  the  bilirubin  is  reduced  by  the  putrefactive  processes  in  the 
intestines,  and  is  conveyed  in  its  reduced  form  by  the  blood  stream  to  the 
kidneys. 

3.  Uro-erythrin  is  the  pigment  which  is  found  in  the  pink  deposits 
of  urates  which  are  sometimes  seen  in  urines;  it  communicates  a  rich 
red-orange  color  to  urine  when  in  solution,  and  its  solutions  have  two 
broad  faint  absorption  bands  in  the  green. 

4.  TJromelanin.  When  urine  is  boiled  with  strong  acids  it  darkens 
to  a  reddish-brown  color.  This  change,  once  ascribed  to  the  formation 
of  a  new  pigment  uromelanin,  is  now  believed  to  be  due  to  the  presence 
in  urine  of  pyrocatechin  and  allied  bodies  which  are  capable  of  taking 
up  oxygen  when  boiled  with  acids,  yielding  C02  and  brown  or  black  re- 
sidual products. 

5.  Indigo  is  found  rarely  in  urines,  to  which  it  may  communicate  a 
blue  or  green  color.  Urine  frequently  contains  a  compound  which  is 
either  a  glucoside,  Indican;  or  more  probably  a  salt  of  indoxyl-sulphuric 
acid.  It  yields  indigo  blue  when  treated  with  strong  hydrochloric  acid 
and  left  to  stand  for  some  hours  exposed  to  the  air;  the  indigo  may  be 
separated  by  treatment  with  boiling  chloroform,  which  takes  it  up, 
forming  a  blue  solution. 

There  is  a  similar  compound  of  skatol  and  sulphuric  acid  which  is 
sometimes  recognized  in  the  urine,  by  the  production  of  a  red  color  when 
nitric  acid  is  added  to  it. 

Many  medicinal  substances  color  the  urine,  for  instance:  Rhubarb. 

Santonin,  Senna,  Fuchsine,  Carbolic  Acid. 

Bromides  and   Iodides  vield  Bromine  or  Iodine,  when  nitric  acid  is 
24 


370  HANDBOOK   OF   PHYSIOLOGY. 

added  to  the  urine  of  patients  taking  these  drugs.  In  the  case  of  iodides 
the  liberated  iodine  communicates  a  strong  mahogany  color  to  the  urine 
thus  treated. 

(5)  Mucus. — Mucus  in  the  urine  consists  principally  of  the  epithe- 
lial debris  from  the  mucous  surface  of  the  urinary  passages.  Particles 
of  epithelium,  in  greater  or  less  abundance,  may  be  detected  in  most 
samples  of  urine,  especially  if  it  has  remained  at  rest  for  some  time,  and 
the  lower  strata  are  then  examined  (Fig.  256).  As  urine  cools,  the 
mucus  is  sometimes  seen  suspended  in  it  as  a  delicate  opaque  cloud,  but 
generally  it  falls.  In  inflammatory  affections  of  the  urinary  passages, 
especially  of  the  bladder,  mucus  in  large  quantities  is  poured  forth,  and 
speedily  undergoes  decomposition.  The  presence  of  the  decomposing 
mucus  excites  chemical  changes  in  the  urea,  whereby  carbonate  of  am- 
monium is  formed,  which,  combining  with  the  excess  of  acid  in  the 
superphosphates  in  the  urine,  produces  insoluble  neutral  or  alkaline 


Fig.  256. — Mucus  deposited  from  urine. 

phosphates  of  calcium  and  magnesium,  and  phosphate  of  ammonium 
and  magnesium.  These  mixing  with  the  mucus,  constitute  the  peculiar 
white,,  viscid,  mortar-like  substance  which  collects  upon  the  mucous  sur- 
face of  the  bladder,  and  is  often  passed  with  the  urine,  forming  a  thick 
tenacious  sediment. 

(6)  Extractives. — In  addition  to  those  already  considered,  urine 
contains  a  considerable  number  of  nitrogenous  compounds.  These  are 
usually  described  under  the  generic  name  of  extractives.  Of  these,  the 
chief  are:  (1)  Kreatinin  (C4H7N30),  a  substance  derived,  probably, 
from  the  metamorphosis  of  muscular  tissue,  crystallizing  in  colorless 
oblique  rhombic  prisms;  a  fairly  definite  amount  of  thk  substance,  about 
15  grains  (1  grm.),  appears  in  the  urine  daily,  so  that  it  must  be  looked 
upon  as  a  normal  constituent;  it  is  increased  on  an  increase  of  the  nitro- 
genous constituents  of  the  food;  (2)  Xantliin  (C6lSr4H402),  an  amorph- 
ous powder  soluble  in  hot  water;  (3)  Hypoxanthin,  or  sarkin  (C0H4N4O); 
(4)  Oxaluric  acid  (C3H4N204),  in  combination  with  ammonium  in  the 
urine  of  the  new-born  child;  (5)  Allantoin  (C4H0N4O3).     All  these  ex- 


STRUCTURE    AND    FUNCTION    OF    THE    KIDNEYS.  371 

tractives  are  chiefly  interesting  as  being  closely  connected  with  urea,  and 
mostly  yielding  that  substance  on  oxidation.  Lcucin  and  ty rosin  can 
scarcely  be  looked  upon  as  normal  constituents  of  urine. 

(7)  Saline  Matter. — (a)  The  sulphuric  acid  in  the  urine  is  com- 
bined chiefly  or  entirely  with  sodium  or  potassium;  forming  salts  which 
are  taken  in  very  small  quantity  with  the  food,  and  are  scarcely  found 
in  other  fluids  or  tissues  of  the  body;  for  the  sulphates  commonly  enu- 
merated among  the  constituents  of  the  ashes  of  the  tissues  and  fluids  are 
for  the  most  part,  or  entirely,  produced  by  the  changes  that  take  place 
in  the  burning.  Only  about  one-third  of  the  sulphuric  acid  found  in 
the  urine  is  derived  directly  from  the  food  (Parkes).  Hence  the  greater 
part  of  the  sulphuric  acid  which  the  sulphates  in  the  urine  contain, 
must  be  formed  in  the  blood,  or  in  the  act  of  secretion  of  urine;  the 
sulphur  of  which  the  acid  is  formed  being  probably  derived  from  the  de- 
composing nitrogenous  tissues,  the  other  elements  of  which  are  resolved 
into  urea  and  uric  acid.  It  may  be  in  part  derived  also  from  the  sul- 
phur-holding taurin  and  cyst  in,  which  can  be  found  in  the  liver,  lungs, 
and  other  parts  of  the  body,  but  not  generally  in  the  excretions;  and 
which,  therefore,  must  be  broken  up.  The  oxygen  is  supplied  through 
the  lungs,  and  the  heat  generated  during  combination  with  the  sulphur, 
is  one  of  the  subordinate  means  by  which  the  animal  temperature  is 
maintained. 

Besides  the  sulphur  in  these  salts,  some  also  appears  to  be  in  the 
urine,  uncombined  with  oxygen;  for  after  all  the  sulphates  have  been 
removed  from  urine,  sulphuric  acid  may  be  formed  by  drying  and  burn- 
ing it  with  nitre.  From  three  to  five  grains  of  sulphur  are  thus  daily 
excreted.  The  combination  in  which  it  exists  is  uncertain:  possibly  it 
is  in  some  compound  analogous  to  cystin  or  cystic  oxide  (Fig.  258).  Sul- 
phuric acid  also  exists  normally  in  the  urine  in  combination  with  phenol 
{C6H60)  as  phenol  sulphuric  acid  or  its  corresponding  salts,  with  so- 
dium, etc. 

(b)  The  phosphoric  acid  in  the  urine  is  combined  partly  with  the  al- 
kalies, partly  with  the  alkaline  earths — about  four  or  five  times' as  much 
with  the  former  as  with  the  latter.  In  blood,  saliva,  and  other  alkaline 
fluids  of  the  body,  phosphates  exist  in  the  form  of  alkaline,  neutral,  or 
acid  salts.  In  the  urine  they  are  acid  salts,  viz.,  the  sodium,  ammo- 
nium, calcium,  and  magnesium  phosphates,  the  excess  of  acid  being 
(Liebig)  due  to  the  appropriation  of  the  alkali  with  which  the  phos- 
phoric acid  in  the  blood  is  combined,  by  the  several  new  acids  which  are 
formed  or  discharged  at  the  kidneys,  namely,  the  uric,  hippuric,  and 
sulphuric  acids,  all  of  which  are  neutralized  with  soda. 

The  phosphates  are  taken  largely  in  both  vegetable,  and  animal  food; 
some  thus  taken  are  excreted  at  once;  others,  after  being  transformed 
and  incorporated  with  the  tissues.     Calcium  phosphate  forms  the  prin- 


372 


HANDBOOK    OF    PHYSIOLOGY. 


cipal  earthy  constituent  of  bone,  and  from  the  decomposition  of  the 
osseous  tissue  the  urine  derives  a  large  quantity  of  this  salt.  The  de- 
composition of  other  tissues  also,  but  especially  of  the  brain  and  nerve- 
substance,  furnishes  large  supplies  of  phosphorus  to  the  urine,  which 
phosphorus  is  supposed,  like  the  sulphur,  to  be  united  with  oxygen,  and 
then  combined  with  bases.  This  quantity  is,  however,  liable  to  con- 
siderable variation.  Any  undue  exercise  of  the  brain,  and  all  circum- 
stances producing  nervous  exhaustion,  increase  it.  The  earthy  phos- 
phates are  more  abundant  after  meals,  whether  on  animal  or  vegetable 
food,  and  are  diminished  after  long  fasting.  The  alkaline  phosphates 
are  increased  after  animal  food,  diminished  after  vegetable  food.  Exer- 
cise increases  the  alkaline,  but  not  the  earthy  phosphates.  Phosphorus 
uncombined  with  oxygen  appears,  like  sulphur,  to  be  excreted  in  the 
urine.  When  the  urine  undergoes  alkaline  fermentation,  phosphates  are 
deposited  in  the  form  of  a  urinary  sediment,  consisting  chiefly  of  ammo- 


Fig.  257 


Fig.  258. 


Fig.  257. —Urinary  sediment  of  triple  phosphates  (large  prismatic  crystals)  and  urate  of  am- 
monium, from  urine  which  had  undergone  alkaline  fermentation. 
Fig.  258— Crystals  of  Cystin. 

nio-magnesium  phosphates  (triple  phosphate)  (Fig.  257).  This  com- 
pound does  not,  as  such,  exist  in  healthy  urine.  The  ammonia  is  chiefly 
or  wholly  derived  from  the  decomposition  of  urea. 

(c)  The  Chlorine  of  the  urine  occurs  chiefly  in  combination  with 
sodium  (next  to  urea,  sodium  chloride  is  the  most  abundant  solid  con- 
stituent of  the  urine),  but  slightly  also  with  ammonium,  and,  perhaps, 
potassium.  As  the  chlorides  exist  largely  in  food,  and  in  most  of  the 
animal  fluids,  their  occurrence  in  the  urine  is  easily  understood. 

(8)  Occasional  Constituents.— Cystin  (C3H7NS02)  (Fig.  258)  is 
an  occasional  constituent  of  urine.  It  resembles  taurin  in  containing  a 
large  quantity  of  sulphur — more  than  25  per  cent.  It  does  not  exist  in 
healthy  urine. 

Another  common  morbid  constituent  of  the  urine  is  Oxalic  acid, 
which  is  frequently  deposited  in  combination  with  calcium  (Fig.  259)  as 


STRUCTURE  AND    FUNCTION    OF    THE    KIDNEYS.  373 

a  urinary  sediment.  Like  cystin,  but  much  more  commonly,  it  is  the 
chief  constituent  of  certain  calculi. 

Of  the  other  abnormal  constituents  of  the  urine  which  were  men- 
tioned on  p.  364,  it  will  be  unnecessary  to  speak  at  length  in  this  work. 

(9)  Gases. — A  small  quantity  of  gas  is  naturally  present  in  the  urine 
in  a  state  of  solution.  It  consists  of  carbonic  acid  (chiefly)  and  nitro- 
gen and  a  small  quantity  of  oxygen. 

The  Method  of  the  Excretion  of  Urine. 

The  excretion  of  the  urine  by  the  kidneys  is  believed  to  consist  of 
two,  more  or  less  distinct  processes — viz.,   (1.)  of  Filtration,  by  which 


Fig.  259.— Crystals  of  Calcium  Oxalate. 

the  water  and  the  ready-formed  salts  are  eliminated;  and,  (2.)  of  True 
Secretion,  by  which  certain  substances  forming  the  chief  and  more  im- 
portant part  of  the  urinary  solids  are  removed  from  the  blood.  This 
division  of  function  corresponds  more  or  less  to  the  division  in  the  func- 
tions of  other  glands  of  which  we  have  already  treated.  It  will  be  as 
well  to  consider  them  separately. 

(1.)  Of  Filtration. — This  part  of  the  renal  function  is  performed 
within  the  Malpighian  corpuscles  by  the  renal  glomeruli.  By  it  not 
only  the  water  is  strained  off,  but  also  certain  other  constituents  of  the 
urine,  e.  g.,  sodium  chloride,  are  separated.  The  amount  of  the  fluid 
filtered  off  depends  almost  entirely  upon  the  blood-pressure  in  the  glo- 
meruli. 

The  greater  the  blood-pressure  in  the  arterial  system  generally,  and 
•consequently  in  the  renal  arteries,  the  greater,  cceteris  paribus,  will  be 
the  blood-pressure  in  the  glomeruli,  and  the  greater  the  quantity  of 
urine  separated  ;  but  even  without  increase  of  the  general  blood-pres- 
sure, if  the  renal  arteries  be  locally  dilated,  the  pressure  in  the  glo 
meruli  will  be  increased  aud  with  it  the  secretion  of  urine.  All  the 
numerous  causes  therefore,  which  increase  the  general  blood-pressure 
{p.  151)  will,  as  a  rule,  secondarily  increase  the  secretion  of  urine.  Of 
these — 


374  HANDBOOK    OF  PHYSIOLOGY. 

(1.)  The  heart's  action  is  amongst  the  most  important.  When  the 
cardiac  contractions  are  increased  in  force,  increased  diuresis  is  the  re- 
sult. 

(2. )  Since  the  connection  between  the  general  blood-pressure  and  the 
nervous  system  is  so  close  it  will  be  evident  that  the  amount  of  urine 
secreted  depends  greatly  upon  the  influence  of  the  latter.  This  may  be 
demonstrated  experimentally.  Thus,  division  of  the  spinal  cord,  by 
producing  general  vascular  dilatation,  causes  a  great  diminution  of 
blood-pressure,  and  so  diminishes  the  amount  of  water  passed;  since  the 
local  dilatation  in  the  renal  arteries  is  not  sufficient  to.  counteract  the 
general  diminution  of  pressure.  Stimulation  of  the  cut  cord  produces, 
strangely  enough,  the  same  results — i.  e.,  a  diminution  in  the  amount  of 
the  urine  passed,  but  in  a  different  way,  viz.,  by  constricting  the  arte- 
ries generally,  and,  among  others,  the  renal  arteries ;  the  diminution  of 
blood-pressure  resulting  from  the  local  resistance  in  the  renal  arteries 
being  more  potent  to  diminish  blood-pressure  in  the  glomeruli  than  the 
general  increase  of  blood-pressure  is  to  increase  it.  Section  of  the 
renal  nerves  or  of  any  others  which  produce  local  dilatation  without 
greatly  diminishing  the  general  blood-pressure  will  cause  an  increase  in 
the  quantity  of  fluid  passed. 

(3.)  The  fact  that  in  summer  or  in  hot  weather  the  urine  is  dimin- 
ished may  be  attributed  partly  to  the  copious  elimination  of  water  by 
the  skin  in  the  form  of  sweat  which  occurs  in  summer,  as  contrasted 
with  the  greatly  diminished  functional  activity  of  the  skin  in  winter, 
but  also  to  the  dilated  condition  of  the  vessels  of  the  skin  causing  a 
decrease  in  the  general  blood-pressure.  Thus  we  see  that  in  regard  to- 
the  elimination  of  water  from  the  system,  the  skin  and  kidneys  perform 
similar  functions,  and  are  capable  to  some  extent  of  acting  vicariously, 
one  for  the  other.  Their  relative  activities  are  inversely  proportional  to 
each  other. 

The  intimate  connection  between  the  condition  of  the  kidney  and  the 
blood-pressure  has  been  exceedingly  well  shown  by  means  of  an  instru- 
ment called  the  Oncometer,  recently  introduced  by  Roy,  which  is  a. 
modification  of  the  plethysmograph  (Fig.  260).  By  meaus  of  this  appa- 
ratus any  alteration  in  the  volume  of  the  kidney  is  communicated  to  an 
apparatus  (oncograph)  capable  of  recording  graphically,  with  a  writing 
lever,  such  variations.  It  has  been  found  that  the  kidney  is  extremely 
sensitive  to  any  alteration  in  the  general  blood-pressure,  every  fall  in  the 
general  blood-pressure  being  accompanied  by  a  decrease  in  the  volume 
of  the  kidney,  and  every  rise,  unless  produced  by  considerable  constric- 
tion of  the  peripheral  vessels,  including  those  of  the  kidney,  being 
accompanied  by  a  corresponding  increase  of  volume.  Increase  of  vol- 
ume is  followed  by  an  increase  in  the  amount  of  urine  secreted,  and 
decrease  of  volume  by  a  decrease  in  the  secretion.     In  addition,  how- 


STRUCTURE    AND    FUNCTION    OF    THE    KIDNEYS. 


375 


ever,  to  the  response  of  the  kidney  to  alterations  in  the  general  blood- 
pressure,  it  has  been  further  observed  that  certain  substances,  when 
injected  into  the  blood,  will  also  produce  an  increase  in  volume  of  the 
kidne}7,  and  consequent  increased  flow  of  urine,  without  affecting  the 
general  blood-pressure — such  bodies  as  sodium  acetate  and  other  diuret- 
ics. These  observations  appear  to  prove  that  local  dilatation  of  the 
renal  vessels  may  be  produced  by  alterations  in  the  blood  acting  upon  a 
local  nervous  mechanism,  as  this  happens  when  all  of  the  renal  nerves 
have  been  divided.  The  alterations  are  not  only  produced  by  the  addi- 
tion of  drugs,  but  also  by  the  introduction  of  comparatively  small 
quantities  of  water  or  saline  solution.  To  this  alteration  of  the  blood 
acting  upon  the  renal  vessels  (either  directly  or)  through  a  local  vaso- 
motor mechanism,  and  not  to  any  great  alteration  in  the  general  blood- 


Fig.  260.— Diagram  of  Roy's  Oncometer,  o,  represents  the  kidney  inclosed  in  a  metal  box 
which  opens  by  hinge  /;  6,  the  renal  vessels  and  duct.  Surrounding  the  kidney  are  two  chambers 
formed  by  membranes,  the  edges  of  which  are  firmly  fixed  by  being  clamped  between  the  outside 
metal  capsule,  and  one  (not  represented  in  the  figure)  inside,  the  two  being  firmly  screwed  together 
by  screws  at  h,  and  below.  The  membranous  chamber  below  is  filled  with  a  varying  amount  of 
warm  oil,  according  to  the  size  of  the  kidney  experimented  with,  through  the  opening  then  closed 
with  the  plug  i.  After  the  kidney  has  been  inclosed  in  the  capsule,  the  membranous  chamber 
above  is  filled  with  warm  oil  through  the  tube  e,  which  is  then  closed  by  a  tap  (not  represented  in 
the  diagram) ;  the  tube  d  communicates  with  a  recording  apparatus,  and  any  alteration  in  the 
volume  of  the  kidney  is  communicated  by  the  oil  in  the  tube  to  the  chamber  d  of  the  Oncograph, 
Fig.  261. 

pressure,  must  we  attribute  the  effects  of  meals,  etc.,  observed  by 
Roberts.  "The  renal  excretion  is  increased  after  meals  and  diminished 
during  fasting  and  sleep.  The  increase  began  within  the  first  hour 
after  breakfast,  and  continued  during  the  succeeding  two  or  three 
hours;  then  a  diminution  set  in,  and  continued  until  an  hour  or  two 
after  dinner.  The  effect  of  dinner  did  not  appear  until  two  or  three 
hours  after  the  meal;  and  it  reached  its  maximum  about  the  fourth 
hour.  From  this  period  the  excretion  steadily  decreased  until  bed-time. 
During  sleep  it  sank  still  lower,  and  reached  its  minimum — being  not 


376 


HANDBOOK    OF    PHYSIOLOGY. 


more  than  one-third  of  the  quantity  excreted  during  the  hours  of  diges- 
tion." The  increased  amount  of  urine  passed  after  drinking  large 
quantities  of  fluid  probably  depends  upon  the  diluted  condition  of  the 
blood  thereby  induced. 


h  l 

Fig.  261.— Roy's  Oncograph,  or  apparatus  for  recording  alterations  in  the  volume  of  the  kidney, 
etc.,  as  shown  by  the  oncometer— a,  upright,  supporting  recording  lever  I,  which  is  raised  or  lowered 
by  needle  b,  which  works  through  /,  and  which  is  attached  to  the  piston  e,  working  in  the  cham- 
ber d,  with  which  the  tube  from  the  oncometer  communicates.  The  oil  is  prevented  from  being 
squeezed  out  as  the  piston  descends  by  a  membrane,  which  is  clamped  between  the  ring-shapec 
surfaces  of  cylinder  by  the  screw  i  working  upwards;  the  tube  h  is  for  filling  the  instrument. 

The  following  table '  will  help  to  explain  the  dependence  of  the  fil- 
tration function  upon  the  blood-pressure  and  the  nervous  system: — 


TABLE    OF   THE   RELATION    OF    THE    SECRETION    OF    URINE    TO   ARTERIAL 

PRESSURE. 

A.  Secretion  of  urine  may  be  increased — 

a.  By  increasing  the  general  Mood-pressure;  by 

1.  Increase  of  the  force  or  frequency  of  heart-beat. 

2.  Constriction  of  the  small  arteries  of  areas  other  than  that 

of  the  kidney. 

b.  By  increasing  the  local  blood-pressure,  by  relaxation  of  the  renal 

artery,  without  compensating  relaxation  elsewhere;  by 

1.  Division  of  the  renal  nerves  (causing  polyuria). 

2.  Division  of  the  renal  nerves  and  stimulation  of  the  cord, 

below  the  medulla  (causing  greater  polyuria). 

3.  Division  of  the  splanchnic  nerves;  but  the  polyuria  pro- 

duced is  less  than  in  1  or  2,  as  these  nerves  are  distrib- 
uted to  a  wider  area,  and  the  dilatation  of  the  renal 
artery  is  accompanied  by  dilatation  of  other  vessels,  and 
therefore  with  a  somewhat  diminished  general  blood- 
supply. 

4.  Puncture  of  the  floor  of  fourth  ventricle  or  mechanical 

irritation  of  the  superior  cervical  ganglion  of  the  sympa- 
thetic, possibly  from  the  production  of  dilatation  of  the 
renal  arteries. 


1  Modified  from  M.  Foster. 


STRUCTURE    AND    FUNCTION    OF    THE    KIDNEYS. 

B.  Secretion  of  urine  may  be  diminished — 


S7T 


a.  By  diminishing  the  general  blood-pressure;  by 

1.  Diminution  of  the  force  or  frequency  of  the  heart-beats. 

2.  Dilatation  of  capillary  areas  other  than  that  of  the  kidney. 

3.  Division  of  spinal  cord  below  the  medulla,  which  causes 

dilatation  of  general  abdominal  area,  and  urine  generally 
ceases  being  secreted. 

b.  By  increasing  the  blood-pressure,  by  stimulation  of  the  spinal 

cord  below  the  medulla,  the  constriction  of  the  renal  artery, 
which  follows  not  being  compensated  for  by  the  increase  of 
general  blood-pressure. 

c.  By  constriction  of  the  renal  artery,  by  stimulating  the  renal  or 

splanchnic  nerves,  or  the  spinal  cord. 


Fig.  262.— Curve  taken  by  renal  oncometer  compared  with  that  of  ordinary  blood-pressure, 
a,  Kidney  curve;  6,  blood-pressure  curve.    (Roy.) 

Although  it  is  convenient  to  call  the  processes  which  go  on  in  the 
renal  glomeruli,  filtration,  there  is  reason  to  believe  that  they  are  not 
absolutely  mechanical,  as  the  term  might  seem  to  imply,  since,  when  the 
epithelium  of  the  Malpighian  capsule  has  been,  as  it  were,  put  out  of 
order  by  ligature  of  the  renal  artery,  on  removal  of  the  ligature,  the 
urine  has  been  found  temporarily  to  contain  albumen,  indicating  that  a 
selective  power  resides  in  the  healthy  epithelium,  which  allows  certain 
constituent  parts  of  the  blood  to  be  filtered  off,  and  not  others. 

(2.)  Of  True  Secretion. — That  there  is  a  second  part  in  the  pro- 
cess of  the  excretion  of  urine,  which  is  true  secretion,  is  suggested  bv 
the  structure  of  the  tubuli  uriniferi,  and  the  idea  is  supported  by  various 
experiments.  It  will  be  remembered  that  the  convoluted  portions  of 
the  tubules  are  lined  with  an  epithelium,  which  bears  a  close  resemblance 
to  the  secretory  epithelium  of  other  glands,  whereas  the  Malpighian 
capsules  and  portions  of  the  loops  of  Henle  are  lined  simply  by  endothe- 
lium. The  two  functions  are,  then,  suggested  by  the  differences  of  epi- 
thelium, and  also  by  the  fact  that  the  blood-supply  is  different,  since 
the  convoluted  tubes  are  surrounded  by  capillary  vessels  derived  from 
the  breaking  up  of  the  efferent  vessels  of  the  Malpighian  tufts.  The 
theory  first  suggested  by  Bowman  (1842),  and  still  generally  accepted. 
of  the  function  of  the  two  parts  of  the  tubules,  is  that  the  cells  of  the 
convoluted  tubes,  by  a  process  of  true  secretion,  separate  from  the  blood 


378  HANDBOOK    OF   PHYSIOLOGY. 

substances  such  as  urea,  whereas  from  the  glomeruli  is  separated  the 
water  and  the  inorganic  salts.  Another  theory  suggested  by  Ludwig 
(1844)  is  that  in  the  glomeruli  are  filtered  off  from  the  blood  all  the  con- 
stituents of  the  urine  in  a  very  diluted  condition.  When  this  passes 
along  the  tortuous  uriniferous  tube,  part  of  the  water  is  reabsorbed  into 
the  vessels  surrounding  them,  leaving  the  urine  in  a  more  concentrated 
condition — retaining  all  its  proper  constituents.  This  osmosis  is  pro- 
moted by  the  high  specific  gravity  of  the  blood  in  the  capillaries  sur- 
rounding the  convoluted  tubes,  but  the  return  of  the  urea  and  similar 
substances  is  prevented  by  the  secretory  epithelium  of  the  tubules.  Lud- 
wig's  theory,  however  plausible,  must,  we  think,  give  way  to  the  first 
theory,  which  is  more  strongly  supported  by  direct  experiment. 

By  using  the  kidney  of  the  newt,  which  has  two  distinct  vascular 
supplies,  one  from  the  renal  artery  to  the  glomeruli,  and  the  other  from 
the  renal-portal  vein  to  the  convoluted  tubes,  Nussbaum  has  shown  that 
certain  substances,  e.  g.,  peptones  and  sugar,  when  injected  into  the 
blood,  are  eliminated  by  the  glomeruli,  and  so  are  not  got  rid  of  when 
the  renal  arteries  are  tied;  whereas  certain  other  substances,  e.  g.,  urea, 
when  injected  into  the  blood,  are  eliminated  by  the  convoluted  tubes, 
even  when  the  renal  arteries  have  been  tied.  This  evidence  is  very  direct 
that  urea  is  excreted  by  the  convoluted  tubes. 

Heidenhain  also  has  shown  by  experiment  that  if  a  substance  (sodium 
sulphindigotate),  which  ordinarily  produces  blue  urine,  be  injected  into 
the  blood  after  section  of  the  medulla  which  causes  lowering  of  the 
blood-pressure  in  the  renal  glomeruli,  that  when  the  kidney  is  examined, 
the  cells  of  the  convoluted  tubules  (and  of  these  alone)  are  stained  with 
the  substance,  which  is  also  found  in  the  lumen  of  the  tubules.  This 
appears  to  show  that  under  ordinary  circumstances  the  pigment  at  any 
rate  is  eliminated  by  the  cells  of  the  convoluted  tubules,  and  that  when 
by  diminishing  the  blood-pressure,  the  filtration  of  urine  ceases,  the  pig- 
ment remains  in  the  convoluted  tubes,  and  is  not,  as  it  is  under  ordinary 
circumstances  swept  away  from  them  by  the  flushing  of  them  which  ordi- 
narily takes  place  with  the  watery  part  of  urine  derived  from  the  glomer- 
uli. It  therefore  is  probable  that  the  cells,  if  they  excrete  the  pigment, 
excrete  urea  and  other  substances  also.  But  urea  acts  somewhat  differ- 
ently to  the  pigment,  as  when  it  is  injected  into  the  blood  of  an  animal 
in  which  the  medulla  has  been  divided,  and  the  secretion  of  urine 
stopped,  a  copious  secretion  of  urine  results,  which  is  not  the  case  when 
the  pigment  is  used  instead  under  similar  conditions.  The  flow  of  urine, 
independent  of  the  general  blood-pressure,  might  be  supposed  to  be  due 
to  the  action  of  the  altered  blood  upon  some  local  vaso-motor  mechanism; 
and,  indeed,  the  local  blood-pressure  is  directly  affected  in  this  way,  but 
there  is  reason  for  believing  that  part  of  the  increase  of  the  secretion  is 


STRUCTURE    AND    FUNCTION    OF   THE    KIDNEYS.  379 

due  to  the  direct  stimulation  of  the  cells  by  the  urea  contained  in  the 
blood. 

To  sum  up,  then,  the  relations  of  the  two  functions:  (1.)  The  process 
of  nitration,  by  which  the  chief  part,  if  not  the  whole,  of  the  fluid  is 
eliminated,  together  with  certain  inorganic  salts,  and  possibly  other 
solids,  is  directly  dependent  upon  blood-pressure,  is  accomplished  by  the 
renal  glomeruli,  and  is  accompanied  by  a  free  discharge  of  solids  from 
the  tubules.  (2.)  The  process  of  secretion  proper,  by  which  urea  and 
the  principal  urinary  solids  are  eliminated,  is  only  indirectly,  if  at  all, 
dependent  upon  blood-pressure,  is  accomplished  by  the  cells  of  the  con- 
voluted tubes,  and  is  sometimes  (as  in  the  case  of  the  elimination  of  urea 
and  similar  substances)  accompanied  by  the  elimination  of  copious  fluid, 
produced  by  the  chemical  stimulation  of  the  epithelium  of  the  same 
tubules. 

Sources  of  the  Nitrogenous  Urinary  Solids. 

Urea. — In  speaking  of  the  method  of  the  secretion  of  urine,  it  was 
assumed  that  the  part  played  by  the  cells  of  the  uriniferous  tubules  was 
that  of  mere  separation  of  the  constituents  of  the  urine  which  existed 
ready-formed  in  the  blood  :  there  is  considerable  evidence  to  favor  this 
assumption.  What  may  be  called  the  specially  characteristic  solid  of 
the  urine,  i.  e.,  urea  (as  well  as  most  of  the  other  solids),  may  be  detected 
in  the  blood,  and  in  other  parts  of  the  body,  e.  g.,  the  humors  of  the  eye, 
even  while  the  functions  of  the  kidneys  are  unimpaired:  but  when  from 
any  cause,  especially  extensive  disease  or  extirpation  of  the  kidneys,  the 
separation  of  urine  is  imperfect,  the  urea  is  found  largely  in  the  blood, 
and  in  most  other  fluids  of  the  body. 

It  must,  therefore,  be  clear  that  the  urea  is  for  the  most  part  made 
somewhere  else  than  in  the  kidneys,  and  simply  brought  to  them  by  the 
blood  for  elimination.  It  is  not  absolutely  proved,  however,  that  all  the 
urea  is  formed  away  from  these  organs,  and  it  is  possible  that  a  small 
quantity  is  actually  secreted  by  the  cells  of  the  tubules.  The  sources  of 
the  urea,  which  is  brought  to  the  kidneys  for  excretion,  may  be  stated 
to  be  the  two. 

(1.)  From  the  splitting  up  the  Elements  of  the  Nitrogenous  Food. — 
The  origin  of  urea  from  this  source  is  shown  by  the  increase  which  en- 
sues on  substituting  an  animal  or  highly  nitrogenous  for  a  vegetable  diet ; 
in  the  much  larger  amount — nearly  double — excreted  by  Carnivora  than 
Herbivora,  independent  of  exercise;  and  in  its  diminution  to  about  one- 
half  during  starvation,  or  during  the  exclusion  of  nitrogenous  principles 
of  food.  Part,  at  any  rate,  of  the  increased  amount  of  urea  which  ap- 
pears in  the  urine  soon  after  a  full  meal  of  proteid  material  may  be  attrib- 
uted to  the  production  of  a  considerable  amount  of  leucin  and  tyrosin 
by  the  pancreatic  digestion.     These  substances  are  carried  by  the  portal 


380  HANDBOOK    OF    PHYSIOLOY. 

rein  to  the  liver,  and  it  is  there  that  the  change  in  all  probability  takes 
place,  as  when  the  functions  of  the  organ  are  gravely  interfered  with,  as 
in  the  case  of  acute  yellow  atrophy,  the  amount  of  urea  is  distinctly 
diminished,  and  its  place  appears  to  be  taken  by  leucin  and  tyrosin.  It 
bas  been  found  by  experiment,  too,  that  if  these  substances  be  introduced 
into  the  alimentary  canal,  the  introduction  is  followed  by  a  correspond- 
ing increase  in  the  amount  of  urea,  but  not  by  the  presence  of  the  bodies 
themselves  in  the  urine. 

(2.)  From  the  Nitrogenous  metabolism  of  the  tissues. — This  second 
source  of  urea  is  shown  by  the  fact  that  that  body  continues  to  be  ex- 
creted, though  in  smaller  quantity  than  usual,  when  all  nitrogenous  sub- 
stances are  strictly  excluded  from  the  food,  as,  for  example,  when  the 
diet  consists  for  several  days  of  sugar,  starch,  gum,  oil,  and  similar  non- 
nitrogenous  substances.  It  is  excreted  also,  even  though  no  food  at  all 
is  taken  for  a  considerable  time;  thus  it  is  found  in  the  urine  of  reptiles 
which  have  fasted  for  months;  and  in  the  urine  of  a  madman,  who  had 
fasted  eighteen  days,  Lassaigne  found  both  urea  and  all  the  components 
of  healthy  urine. 

Turning  to  the  muscles,  however,  as  the  most  actively  metabolic  tis- 
sue, we  find  as  a  result  of  their  activity  not  urea,  but  Kreatin;  and  al- 
though it  may  be  supposed  that  some  of  this  latter  body  appears  natu- 
rally in  the  urine,  as  Kreatinin,  or  hydrated  Kreatin,  yet  it  is  not  in 
sufficient  quantity  to  represent  the  large  amount  of  it  formed  by  the 
muscles,  and,  indeed,  by  others  of  the  tissues.  It  is  assumed  that  krea- 
tin, therefore,  is  the  nitrogenous  antecedent  of  urea;  where  its  conver- 
sion into  urea  takes  place  is  doubtful,  but  very  likely  the  liver,  and 
possibly  the  spleen,  may  be  the  seat  of  the  change.  It  is  possible,  how- 
ever, that  part — but  if  so,  a  small  part — reaches  the  kidneys  without 
previous  change,  leaving  it  to  the  cells  of  the  renal  tubules  to  complete 
the  action.  In  speaking  of  kreatin  as  the  antecedent  of  urea,  it  should  be 
recollected  that  other  nitrogenous  products,  suchasxanthin  (C5H4]Sr402), 
appear  in  conjunction  with  it,  and  that  these  may  also  be  converted  into 
urea. 

It  was  formerly  taken  for  granted  that  the  quantity  of  urea  in  the 
urine  is  greatly  increased  by  active  exercise;  but  numerous  observers 
have  failed  to  detect  more  than  a  slight  increase  under  such  circum- 
stances; and  our  notions  concerning  the  relation  of  this  excretory  pro- 
duct to  the  destruction  of  muscular  fibre,  consequent  on  the  exercise  of 
the  latter,  have  undergone  considerable  modification.  There  is  no  doubt, 
of  course,  that  like  all  parts  of  the  body,  the  muscles  have  but  a  limited 
term  of  existence,  and  are  being  constantly,  although  very  slowly,  re- 
newed, at  the  same  time  that  a  part  of  the  products  of  their  disintegra- 
tion appears  in  the  urine  in  the  form  of  urea.  But  the  waste  is  not  so 
fast  as  it  was  formerly  supposed  to  be;  and  the  theory  that  the  amount  of 


STRUCTURE    AND    FUNCTION    OF    THE    KIDNEYS.  36l 

work  done  by  the  muscles  is  expressed  by  the  quantity  of  urea  excreted 
in  the  urine  must  without  doubt  be  given  up. 

Uric  Acid. — Uric  acid  probably  arises  much  in  the  same  way  as  urea, 
either  from  the  disintegration  of  albuminous  tissues,  or  from  the  food. 
The  relation  which  uric  acid  and  urea  bear  to  each  other  is,  however, 
still  obscure;  but  uric  acid  is  said  to  be  a  less  advanced  stage  of  the  oxi- 
dation of  the  products  of  proteid  metabolism.  The  fact  that  they  often 
exist  together  in  the  same  urine  makes  it  seem  probable  that  they  have 
different  origins;  but  the  entire  replacement  of  either  by  the  other,  as 
of  urea  by  uric  acid  in  the  urine  of  birds,  serpents,  and  many  insects, 
and  of  uric  acid  by  urea,  in  the  urine  of  the  feline  tribe  of  Mammalia, 
shows  that  either  alone  may  take  the  place  of  the  two.  At  any  rate,  al- 
though it  is  true  that  one  molecule  of  uric  acid  is  capable  of  splitting  up 
into  two  molecules  of  urea  and  one  of  mes-oxalic  acid,  there  is  no  evi- 
dence for  believing  that  uric  acid  is  an  antecedent  of  urea  in  the  nitro- 
genous metabolism  of  the  body.  Some  experiments  seem  to  show  that 
uric  acid  is  formed,  at  any  rate  in  part,  in  the  kidney. 

Hippuric  Acid  (C9H9N03). — The  source  of  hippuric  acid  is  not 
satisfactorily  determined;  in  part  it  is  probably  derived  from  some  con- 
stituents of  vegetable  diet,  though  man  has  no  hippuric  acid  in  his  food, 
nor,  commonly,  any  benzoic  acid  that  might  be  converted  into  it;  in 
part  from  the  natural  disintegration  of  tissues,  independent  of  vegetable 
food,  for  Weismann  constantly  found  an  appreciable  quantity,  even  when 
living  on  an  exclusively  animal  diet.  Hippuric  acid  arises  from  the  union 
of  benzoic  acid  withglyciu  (C2H5N02  +  C7H602  =  C9H9N03  +  naO),  which 
union  may  take  place  in  the  kidneys  themselves,  as  well  as  in  the 
liver. 

Extractives. — The  source  of  the  extractives  of  the  urine  is  proba- 
bly in  chief  part  the  disintegration  of  the  nitrogenous  tissues,  but  we  are 
unable  to  say  whether  these  nitrogenous  bodies  are  merely  accidental, 
having  resisted  further  decomposition  into  urea,  or  whether  they  are  the 
representatives  of  the  decomposition  of  special  tissues,  or  of  special  forms 
of  metabolism  of  the  tissues.  There  is,  however,  one  exception,  and 
this  is  in  the  case  of  kreatinin ;  there  is  great  reason  for  believing  that 
the  amount  of  this  body  which  appears  in  the  urine  is  derived  from  the 
metabolism  of  the  nitrogenous  food,  as  when  this  is  diminished,  it  di- 
minishes, and  when  stopped,  it  no  longer  appears  in  the  urine. 

The  Passage  of  Urine  into  the  Bladder. 

As  each  portion  of  urine  is  secreted  it  propels  that  which  is  already 
in  the  uriniferous  tubes  onwards  into  the  pelvis  of  the  kidney.  Thence 
through  the  ureter  the  urine  passes  into  the  bladder,  into  which  its  rate 
and  mode  of  entrance  has  been  watched  in  cases  of  ectopia  vesica',  i.  e., 
of  such  fissures  in  the  anterior  or  lower  part  of  the  walls  of  the  abdomen. 


3S2  HANDBOOK    OF    PHYSIOLOGY. 

and  of  the  front  wall  of  the  bladder,  as  expose  to  view  its  hinder  wall  to- 
gether with  the  orifices  of  the  ureters.  The  urine  does  not  enter  the 
bladder  at  any  regular  rate,  nor  is  there  a  synchronism  in  its  movement 
through  the  two  ureters.  During  fasting,  two  or  three  drops  enter  the 
bladder  every  minute,  each  drop  as  it  enters  first  raising  up  the  little 
papilla  on  which,  in  these  cases,  the  ureter  opens,  and  then  passing 
slowly  through  its  orifice,  which  at  once  again  closes  like  a  sphincter.  In 
the  recumbent  posture,  the  urine  collects  for  a  little  time  in  the  ureters, 
then  flows  gently,  and,  if  the  body  be  raised,  runs  from  them  in  a  stream 
till  they  are  empty.  Its  flow  is  increased  in  deep  inspiration,  or  strain- 
ing, and  in  active  exercise,  and  in  fifteen  or  twenty  minutes  after  a  meal. 
The  urine  collecting  is  prevented  from  regurgitation  into  the  ureters  by 
the  mode  in  which  these  pass  through  the  walls  of  the  bladder,  namely, 
by  their  lying  for  between  half  and  three-quarters  of  an  inch  between 
the  muscular  and  mucous  coats  before  they  turn  rather  abruptly  forwards, 
and  open  through  the  latter  into  the  interior  of  the  bladder. 

Micturition. — The  contraction  of  the  muscular  walls  of  the  bladder 
may  by  itself  expel  the  urine  with  little  or  no  help  from  other  muscles. 
In  so  far,  however,  as  it  is  a  voluntary  act,  it  is  performed  by  means  of 
the  abdominal  and  other  expiratory  muscles,  which  in  their  contraction, 
as  before  explained,  press  on  the  abdominal  viscera,  the  diaphragm  being 
fixed,  and  cause  the  expulsion  of  the  contents  of  those  whose  sphincter 
muscles  are  at  the  same  time  relaxed.  The  muscular  coat  of  the  bladder 
co-operates,  in  micturition,  by  reflex  involuntary  action,  with  the  ab- 
dominal muscles;  and  the  act  is  completed  by  the  accelerator  urince 
which,  as  its  name  implies,  quickens  the  stream,  and  expels  the  last  drops 
of  urine  from  the  urethra.  The  act,  so  far  as  it  is  not  directed  by  voli- 
tion, is  under  the  control  of  a  nervous  centre  in  the  lumbar  spinal  cord, 
through  which,  as  in  the  case  of  the  similar  centre  for  defsecation,  the 
various  muscles  concerned  are  harmonized  in  their  action.  It  is  well 
known  that  the  act  may  be  reflexly  induced,  e.  g.,  in  children  who  suffer 
from  intestinal  worms,  or  other  such  irritation.  Generally  the  afferent 
impulse  which  calls  into  action  the  desire  to  micturate  is  excited  by  ovei- 
distention  of  the  bladder,  or  even  by  a  few  drops  of  urine  passing  into 
the  urethra. 


CHAPTER   XIII. 

THE  VASCULAR  GLANDS. 

In  addition  to  the  various  glands  the  structure  and  functions  of  which 
have  been  considered  in  the  preceding  chapters,  and  which  have  been 
shown  either  to  secrete  from  the  blood  materials  of  use  in  digestion  or 
to  excrete  from  the  blood  materials  of  no  further  use  in  the  economy, 
there  are  others  which  have  not  to  do  with  secretion  or  excretion,  at  all 
events  directly.  Those  are  called  Vascular  glands,  and  comprise  the 
Spleen,  the  Thymus  gland,  the,  Tonsils,  and  the  Solitary  and  Agminated 
glands  of  Peyer  in  the  intestine,  all  of  which  are  made  up  chiefly  of 
lymphatic  tissue,  resembling  lymphatic  glands,  and  which  are  evidently 
closely  connected  with  the  lymphatic  system;  the  Supra-renal  capsules 
or  Adrenals;  the  Thyroid  gland;  the  Pineal  and  Pituitary  glands  and 
the  Carotid  and  Coccygeal  glands. 

The  Spleen. 

The  spleen  is  the  largest  of  these  so-called  vascular  glands;  it  is  situ- 
ated to  the  left  of  the  stomach,  between  it  and  the  diaphragm.  It  is  of 
a  deep  red  color,  of  a  variable  shape,  generally  oval,  somewhat  concavo- 
convex.     Vessels  enter  and  leave  the  gland  at  the  inner  side  or  hilus. 

Structure. — The  spleen  is  covered  externally  almost  completely  by  a 
serous  coat  derived  from  the  peritoneum,  while  within  this  is  the  proper 
fibrous  coat  or  capsule  of  the  organ.  The  latter,  composed  of  connective 
tissue,  with  a  large  preponderance  of  elastic  fibres,  and  a  certain  propor- 
tion of  unstriated  muscular  tissue,  forms  the  immediate  investment  of 
the  spleen.  Prolonged  from  its  inner  surface  are  fibrous  processes  or 
trabeculce,  containing  much  unstriated  muscle,  which  enter  the  interior 
of  the  organ,  and,  dividing  and  anastomosing  in  all  parts,  form  a  kind 
of  supporting  frame-work  or  stroma,  in  the  interstices  of  which  the 
proper  substance  of  the  spleen  (spleen  pulp)  is  contained  (Fig.  264).  At 
the  hilus  of  the  spleen,  the  blood-vessels,  nerves,  and  lymphatics  enter, 
and  the  fibrous  coat  is  prolonged  into  the  spleen-substance  in  the  form 
of  investing  sheaths  for  the  arteries  and  veins,  which  sheaths  again  are 
continuous  with  the  trabecules  before  referred  to. 

The  spleen-pulp,  which  is  of  a  dark-red  or  reddish-brown  color,  is 


384 


HANDBOOK    OF    PHYSIOLOGY. 


composed  chiefly  of  cells,  imbedded  in  a  matrix  of  fibres  formed  of  the 
branchings  of  large  flattened  nucleated  endotheloid  cells.  The  spaces  of 
the  network  only  partially  occupied  by  cells  form  a  freely  communicat- 
ing system.  Of  the  cells  some  are  granular  corpuscles  resembling  the 
lymph-corpuscles,  more  or  less  connected  with  the  cells  of  the  meshwork, 
both  in  general  appearance  and  in  being  able  to  perform  anneboid  move- 
ments; others  are  red  blood-  corpuscles  of  normal  appearance  or  variously 
changed;  while  there  are  also  large  cells  containing  either  a  pigment  al- 
lied to  the  coloring  matter  of  the  blood,  or  rounded  corpuscles  like  red 
blood-corpuscles. 


Fig.  263. 


Fig.  264. 


Fig.  263.— Section  of  dog's  spleen  injected:  c,  capsule;  tr,  trabeculae;  m,  two  Malpighian  bodies 
with  numerous  small  arteries  and  capillaries :  a,  artery,  I,  lymphoid  tissue,  consisting  of  closely- 
packed  lymphoid  cells  supported  by  very  delicate  retiform  tissue;  a  light  space  unoccupied  by  ceils 
is  seen  all  around  the  trabeculae,  which  corresponds  to  the  "lymph  path"  in  lymphatic  glands. 
( Schofield.) 

Fig.  261.— Reticulum  of  the  spleen  of  a  Cat,  shown  by  injection  with  gelatin  and  silver  nitrate. 
(Cadiat.) 


The  splenic  artery,  after  entering  the  spleen  by  its  concave  surface, 
divides  and  subdivides,  with  but  little  anastomosis  between  its  branches; 
at  the  same  time  its  branches  are  sheathed  by  the  prolongations  of  the 
fibrous  coat,  which  they,  so  to  speak,  carry  into  the  spleen  with  them. 
The  arteries  send  off  branches  into  the  spleen-pulp  which  end  in  capil- 
laries, and  these  either  communicate,  as  in  other  parts  of  the  body,  with 


THE    VASCULAR    GLANDS.  38l> 

the  radicles  of  the  veins,  or  end  in  lacunar  spaces  in  the  spleen-pulp, 
from  which  veins  arise. 

The  walls  of  the  smaller  veins  are  more  or  less  incomplete,  and 
readily  allow  lymphoid  corpuscles  to  be  swept  into  the  blood-current. 
The  blood  from  the  arterial  capillaries  is  emptied  into  a  system  of  inter- 
mediate passages,  which  are  directly  bounded  by  the  cells  and  fibres  of 
the  network  of  the  pulp,  and  from  which  the  smallest  venous  radicles 
with  their  cribriform  walls  take  origin  (Frey).  The  veins  are  large  and 
very  distensible;  the  whole  tissue  of  the  spleen  is  highly  vascular,  and 
becomes  readily  engorged  with  blood:  the  amount  of  distention  is,  how- 
ever, limited  by  the  fibrous  and  muscular  tissue  of  its  capsule  and 
trabecular,  which  forms  an  investment  and  support  for  the  pulpy  mass 
within. 

On  the  face  of  a  section  of  the  spleeu  can  be  usually  seen  readily  with 
the  naked  eye,  minute,  scattered  rounded  or  oval  whitish  spots,  mostly 
from  ^L-  to  ^V  inch  in  diameter.  These  are  the  Malpighian  corpuscles 
of  the  spleen,  and  are  situated  on  the  sheaths  of  the  minute  splenic  ar- 
teries, of  which,  indeed,  they  may  be  said  to  be  outgrowths  (Fig.  263). 
For  while  the  sheaths  of  the  larger  arteries  are  constructed  of  ordinary 
connective  tissue,  this  has  become  modified  where  it  forms  an  invest- 
ment for  the  smaller  vessels,  so  as  to  be  composed  of  adenoid  tissue,  with 
abundance  of  corpuscles,  like  lymph-corpuscles,  contained  in  its  meshes, 
and  the  Malpighian  corpuscles  are  but  small  outgrowths  of  this  cyto- 
genous  or  cell-bearing  connective  tissue.  They  are  composed  of  cylin- 
drical masses  of  corpuscles,  intersected  in  all  parts  by  a  delicate  fibrillar 
tissue,  which,  though  it  invests  the  Malpighian  bodies,  does  not  form  a 
complete  capsule.  Blood-capillaries  traverse  the  Malpighian  corpuscles 
and  form  a  plexus  in  their  interior.  The  structure  of  a  Malpighian  cor- 
puscle of  the  spleen  is,  therefore,  very  similar  to  that  of  lymphatic-gland 
substance. 

Functions. — With  respect  to  the  office  of  the  spleen,  we  have  the  fol- 
lowing data:  (1.)  The  large  size  which  it  gradually  acquires  towards  the 
termination  of  the  digestive  process,  and  the  great  increase  observed 
about  this  period  in  the  amount  of  the  finely-granular  albuminous  plasma 
within  its  parenchyma,  and  the  subsequent  gradual  decrease  of  this  ma- 
terial, seem  to  indicate  that  this  organ  is  concerned  in  elaborating  the  al- 
buminous materials  of  the  food,  and  for  a  time  storing  them  up,  to  be 
gradually  introduced  into  the  blood,  according  to  the  demands  of  the 
general  system. 

(2.)  It  seems  probable  that  the  spleen,  like  the  lymphatic  glands,  is 
engaged  in  the  formation  of  blood-corpuscles.  For  it  is  quite  certain 
that  the  blood  of  the  splenic  vein  contains  an  unusually  large  amount  of 
white  corpuscles;  and  in  the  disease  termed  leucocythaemia,  in  which  the 
pale  corpuscles  of  the  blood  are  remarkably  increased  in  number,  there 
25 


386  HANDBOOK   OF   PHYSIOLOGY. 

is  almost  always  found  an  hypertrophied  state  of  the  spleen  or  of  the 
lymphatic  glands.  In  Kolliker's  opinion,  the  development  of  colorless 
and  also  colored  corpuscles  of  the  blood  is  one  of  the  essential  functions 
of  the  spleen,  into  the  veins  of  which  the  new-formed  corpuscles  pass, 
and  are  thus  conveyed  into  the  general  current  of  the  circulation. 

(3.)  There  is  reason  to  believe,  that  in  the  spleen  many  of  the  red 
corpuscles  of  the  Mood,  those  probably  which  have  discharged  their  office 
and  are  worn  out,  undergo  disintegration;  for  in  the  colored  portions  of 
the  spleen-pulp  an  abundance  of  such  corpuscles,  in  various  stages  of 
degeneration,  are  found,  while  the  red  corpuscles  in  the  splenic  venous 
hlood  are  said  to  be  relatively  diminished.  This  process  appears  to  be  as 
follows.  The  blood-corpuscles,  becoming  smaller  and  darker,  collect 
together  in  roundish  heaps,  which  may  remain  in  this  condition,  or  be- 
come each  surrounded  by  a  cell-wall.  The  cells  thus  produced  may  con- 
tain from  one  to  twenty  blood-corpuscles  in  their  interior.  These  cor- 
puscles become  smaller  and  smaller;  exchange  their  red  for  a  golden- 
yellow,  brown,  or  black  color;  and  at  length,  are  converted  into  pigment- 
granules,  which  by  degrees  become  paler  and  paler,  until  all  color  is  lost. 
The  corpuscles  undergo  these  changes  whether  the  heaps  of  them  are  en- 
veloped by  a  cell-wall  or  not. 

(4.)  From  the  almost  constant  presence  of  uric  acid,  in  larger  quan- 
tities than  in  other  organs,  as  well  as  of  the  nitrogenous  bodies,  xanthin,' 
hypoxanthin,  and  leucin,  in  the  spleen,  some  special  nitrogenous  meta- 
bolism may  be  fairly  inferred  to  occur  in  it. 

(5.)  Besides  these,  its  supposed  direct  offices,  the  spleen,  is  believed 
to  fulfil  some  purpose  in  regard  to  the  portal  circulation,  with  which  it 
is  in  close  connection.  From  the  readiness  with  which  it  admits  of  being 
distended,  and  from  the  fact  that  it  is  generally  small  while  gastric  di- 
gestion is  going  on,  and  enlarges  when  that  act  is  concluded,  it  is  sup- 
posed to  act  as  a  kind  of  vascular  reservoir,  or  diverticulum  to  the  portal 
system,  or  more  particularly  to  the  vessels  of  the  stomach.  That  it  may 
serve  such  a  purpose  is  also  made  probable  by  the  enlargement  which  it 
undergoes  in  certain  affections  of  the  heart  and  liver,  attended  with  ob- 
struction to  the  passage  of  blood  through  the  latter  organ,  and  by  its 
diminution  when  the  congestion  of  the  portal  system  is  relieved  by  dis~_ 
charges  from  the  bowels,  or  by  the  effusion  of  blood  into  the  stomach. 
This  mechanical  influence  on  the  circulation,  however,  can  hardly  be 
supposed  to  be  more  than  a  very  subordinate  function. 

It  is  only  necessary  to  mention  that  Schiff  believes  that  the  spleen 
manufactures  a  substance  without  which  the  pancreatic  secretion  cannot 
act  upon  proteids,  so  that  when  the  spleen  is  removed  the  digestive  ac- 
tion of  the  pancreatic  juice  is  stopped. 

Influence  of  the  Nervous  System  upon  the  Spleen. — When  the  spleen 


THE    VASCULAR    GLANDS. 


33, 


is  enlarged  after  digestion,  its  enlargement  is  probably  due  to  two  causes, 
(1)  a  relaxation  of  the  muscular  tissue  which  forms  so  large  a  part  of  its 
framework;  (2)  a  dilatation  of  the  vessels.  Both  these  phenomena  are 
doubtless  under  control  of  the  nervous  system.  It  has  been  found  by 
experiment  that  when  the  splenic  nerves  are  cut  the  spleen  enlarges,  and 
that  contraction  can  be  brought  about  (1)  by  stimulation  of  the  spinal 
cord  (or  of  the  divided  nerves);  (2)  reflexly  by  stimulation  of  the  central 
stumps  of  certain  divided  nerves,  e.g.,  vagus  and  sciatic;  (3)  by  local 
stimulation  by  an  electric  current;  (4)  the  exhibition  of  quinine  and 
some  other  drugs.  It  has  been  shown  by  the  oncometer  of  Roy  (Fig. 
260),  that  the  spleen  undergoes  rhythmical  contractions  and  dilatations, 
due  no  doubt  to  the  contraction  and  relaxation  of  the  muscular  tissue  in 
its  capsule  and  trabecular  It  also  shows  the  rhythmical  alteration  of 
the  general  blood-pressure,  but  to  a  less  extent  than  the  kidney. 

The  Thymus. 

This  gland  must  be  looked  upon  as  a  temporary  organ,  as  it  attains 
its  greatest  size  early  after  birth,  and  after  the  second  year  gradually 


A  ■%. 


•^v.-::-:;/  ■■•;■■::..   .i'-;.-;V 

>.'<  "  ' ,    <4 

v  '•:••■.?;•.■•  •  •  ••  ■'  ~, 


Fig.  265.  Fig.  266.        I  Fig.  267. 

Fig.  265.— Transverse  section  of  a  lobule  of  an  injected  infantile  thymus  gland,  a,  capsule  of 
connective  tissue  surrounding  the  lobule;  b,  membrane  of  the  glandular  vesicles;  c.  eavitv  of  the 
lobule,  from  which  the  larger  blood-vessels  are  seen  to  extend  towards  and  ramify  in  the  spheroidal 
masses  of  the  lobule.     \  80.    (KOlliker.") 

Fig.  266.— From  a  horizontal  section  through  superficial  part  of  the  thymus  of  a  calf,  slightly 
.magnified.  Showing  in  the  centre  a  follicle  of  polygonal  shape  with  similarly  shaped  follicles  round 
it.    (Klein  and  Noble  Smith.) 

Fig.  267.—  The  reticulum  of  the  Thymus,  o,  epithelial  elements;  b,  corpuscles  of  Hassall. 
(Cadiat.) 


diminishes,  until  in  adult  life  hardly  a  vestige  remains.     At  its  greatest 
development  it  is  a  long  narrow  body,  situated  in  the  front  of  the  chest 


388  HANDBOOK    OF    PHYSIOLOGY. 

behind  the  sternum  and  partly  in  the  lower  part  of  the  neck.  It  is  of  a 
reddish  or  grayish  color,  distinctly  lobulated. 

Structure. — The  gland  is  surrounded  by  a  fibrous  capsule,  which 
sends  in  processes,  forming  trabecular,  which  divide  the  glands  into 
lobes,  and  carry  the  blood  and  lymph- vessels.  The  large  trabecular 
branch  into  small  ones,  which  divide  the  lobes  into  lobules.  The  gland 
is  incased  in  a  fold  of  the  pleura.  The  lobules  are  further  subdivided 
into  follicles  by  fine  connective  tissue.  A  follicle  (Fig.  266)  is  seen  on 
section  to  be  more  or  less  polyhedral  in  shape,  and  consists  of  cortical 
and  medullary  portions,  both  of  which  are  composed  of  adenoid  tissue, 
but  in  the  medullary  portion  the  matrix  is  coarser,  and  is  not  so  filled 
up  with  lymphoid  corpuscles  as  in  the  cortex.  The  adenoid  tissue  of 
the  cortex,  and  to  a  less  marked  extent  that  of  the  medulla,  consists  of 
two  elements,  one  with  small  meshes  formed  of  fine  fibres  with  thickened 
nodal  points,  and  the  other  inclosed  within  the  first,  composed  of 
branched  connective-tissue  corpuscles  (Watney).  Scattered  in  the  ade- 
noid tissue  of  the  medulla  are  the  concentric  corpuscles  of  Hassall,  which 
are  protoplasmic  masses  of  various  sizes,  consisting  of  a  nucleated  gran- 
ular centre,  surrounded  by  flattened  nucleated  endothelial  cells.  In  the 
reticulum,  especially  of  the  medulla,  are  large  transparent  giant  cells. 
In  the  thymus  of  the  dog  and  of  other  animals  are  to  be  found  cysts, 
probably  derived  from  the  concentric'  corpuscles,  some  of  which  are 
lined  with  ciliated  epithelium,  and  others  with  short  columnar  cells. 
Haemoglobin  is  found  in  the  thymus  of  all  animals,  either  in  these  cysts, 
or  in  cells  near  to  or  of  the  concentric  corpuscles.  In  the  lymph  issuing 
from  the  thymus  are  cells  containing  colored  blood-corpuscles  and  haemo- 
globin granules,  and  in  the  lymphatics  of  the  thymus  there  are  more 
colorless  cells  than  in  the  lymphatics  of  the  neck.  In  the  blood  of  the 
thymic  vein,  there  appears  sometimes  to  be  an  increase  in  the  colorless 
corpuscles,  and  also  masses  of  granular  matter  (corpuscles  of  Zimmer- 
mann)  (Watney).  The  arteries  radiate  from  the  centre  of  the  gland. 
Lymph  sinuses  may  be  seen  occasionally  surrounding  a  greater  or  smaller 
portion  of  the  periphery  of  the  follicles  (Klein).  The  nerves  are  very 
minute. 

Function. — The  thymus  appears  to  take  part  in  producing  colored 
corpuscles,  both  from  the  large  corpuscles  containing  haemoglobin,  and 
also  indirectly  from  the  colorless  corpuscles  (Watney). 

Eespecting  the  thymus  gland  in  the  hybernating  animals,  in  which 
it  exists  throughout  life,  as  each  successive  period  of  hybernation  ap- 
proaches, the  thymus  greatly  enlarges  and  becomes  laden  with  fat, 
which  accumulates  in  it  and  in  fat  glands  connected  with  it,  in  even 
larger  proportions  than  it  does  in  the  ordinary  seats  of  adipose  tissue. 
Hence  it  appears  to  serve  for  the  storing  up  of  materials  which,  being 
reabsorbed  in  inactivity  of  the  hybernating  period,  may  maintain  the 


THE    VASOL'LAR    GLANDS. 


389 


respiration  and  the  temperature  of  the  body  in  the  reduced  state  to 
which  they  fall  during  that  time.  It  has  been  shown  also  to  be  a  source 
of  the  red  blood-corpuscles,  at  any  rate  in  early  life. 

The  Thyroid. 

The  thyroid  gland  is  situated  in  the  neck.  It  consists  of  two  lobes 
one  on  each  side  of  the  trachea  extending  upwards  to  the  thyroid  carti- 
lage, covering  its  inferior  cornu  and  part  of  its  body;  these  lobes  are 
connected  across  the  middle  line  by  a  middle  lobe  or  isthmus.  The  thy- 
roid is  covered  by  the  muscles  of  the  neck.  It  is  highly  vascular,  and 
varies  in  size  in  different  individuals. 

Structure. — The  gland  is  encased  in  a  thin  transparent  layer  of  dense 
areolar  tissue,,  free  from  fat,  containing  elastic  fibres.  This  capsule 
sends  in  strong  fibrous  trabecular,  which  inclose  the  thyroid  vesicles  — 


Fig.  268.— Part  of  a  section  of  the  human  Thyroid,  a,  fibrous  capsule;  b,  thyroid  vesicles  filled 
with,  e,  colloid  substance ;  c,  supporting  fibrous  tissue;  d,  short  columnar  cells  lining  vesicles;  /, 
-arteries;  g,  veins  filled  with  blood  ;h,  lymphatic  vessel  filled  with  colloid  substance.  X  (S.  K  Alcock.  > 

which  are  rounded  or  oblong  irregular  sacs,  consisting  of  a  wall  of  thin 
hyaline  membrane  lined  by  a  single  layer  of  short  cylindrical  or  cubical 
cells.  These  vesicles  are  filled  with  a  coagulable  fluid  or  transparent 
•colloid  material.  The  colloid  substance  increases  with  age,  and  the  cav- 
ities appear  to  coalesce.     In  the  interstitial  connective  tissue  is  a  round- 


390 


HANDBOOK    OF    PHYSIOLOGY. 


meshed  capillary  plexus,  and  a  large  number  of  lymphatics.  The  nerves 
adhere  closely  to  the  vessels. 

In  the  vesicles  there  are  in  addition  to  the  yellowish  glassy  colloid 
material,  epithelium  cells,  colorless  blood-corpuscles,  and  also  colored 
corpuscles  undergoing  disintegration. 

Function. — There  is  little  known  definitely  about  the  function  of  the 
thyroid  body.  It,  however,  produces  colloid  material  of  the  vesicle, 
which  is  carried  off  by  the  lymphatics,  and  discharged  into  the  blood, 
and  so  may  contribute  its  share  to  the  elaboration  of  that  fluid.  The 
destruction  of  red  blood-corpuscles  is  also  supposed  to  go  on  in  the  gland. 
In  certain  animals  its  removal  appears  to  produce  a  peculiar  condition  in 
which  mucin  is  deposited  in  its  tissues.  A  similar  condition,  known  as 
Myxcedema,  and  Cretinism  are  closely  associated  with  disease  or  removal 
of  the  thyroid  gland  in  the  human  subject. 

Supra-renal  Capsules  or  Adrenals. 

These  are  two  flattened,  more  or  less  triangular  or  cocked-hat  shaped 
bodies,  resting  by  their  lower  border  upon  the  upper  border  of  the  kid- 
neys. 


Fig.  269.— Vertical  section  through  part  of  the  cortical  portion  of  supra-renal  of  guinea-pig.  a, 
capsule;  b,  zona  glomerulosa;  c,  zona  fasciculata;  d,  connective  tissue  supporting  the  columns  of  the 
cells  of  the  latter,  and  also  indicating  the  position  of  the  blood-vessels.     X    (S.  K.  Alcock.) 


Structure.—  The  gland  is  surrounded  by  an  outer  sheath  of  connec- 
tive tissue,  which  sometimes  consists  of  two  layers,  sending  in  exceed- 
ingly  fine  prolongations   forming  the  framework   of   the  gland.     The 


THE    VASCULAR    GLANDS. 


391 


gland  tissue  proper  consists  of  an  outside  firmer  cortical  portion,  and  an 
inside  soft  dark  medullary  portion. 

(1.)  The  cortical  portion  is  divided  into  (Fig.  269)  an  external  nar- 
row layer  of  small  rounded  or  oval  spaces,  the  zona  glomerulosa,  made 
by  the  fibrous  trabecular,  containing  multinucleated  masses  of  proto- 
plasm, the  differentiation  of  which  into  distinct  cells,  cannot  be  made 
out.  (b)  A  layer  of  cells  arranged  radially,  the  zona  fasciculata  (c). 
The  substance  of  this  layer  is  broken  up  into  cylinders,  each  of  which 
is  surrounded  by  the  connective-tissue  framework.  The  cylinders  thus 
produced  are  of  three  kinds — one  containing  an  opaque,  resistant,  highly 
refracting  mass  (probably  of  a  fatty  nature);  frequently  a  large  number 
of  nuclei  are  present;  the  individual  cells  can  only  be  made  out  with 
difficulty.  The  second  variety  of  cylinders  is  of  a  brownish  color,  and 
contains  finely  granular  cells,  in  which  are  fat  globules.  The  third 
variety  consists  of  gray  cylinders,  containing  a  number  of  cells  whose 
nuclei  are  filled  with  a  large  number  of  fat  granules.  The  third  layer 
of  the  cortical  portion  is  the  zona  reticularis  (not  shown  in  Fig.  269). 
This  layer  is  apparently  formed  by  the  breaking  up  of  the  cylinders,  the 
elements  being  dispersed  and  isolated.  The  cells  are  finely  granular, 
and  have  no  deposit  of  fat  in  their  interior:  but  in  some  specimens  fat 
may  be  present,  as  well  as  certain  large  yellow  granules,  which  may  be 
called  pigment  granules. 

(2.)  The  medullary  substance  consists  of  a  coarse  rounded  or  ir- 


Fig.  270—  Section  through  a  portion  of  the  medullary  part  of  the  suprarenal  of  guinea-pig. 
The  vessels  are  very  numerous,  and  the  fibrous  stroma  more  distinct  than  in  the  cortex;  and  is 
moreover  reticulated.    The  cells  are  irregular  and  larger,  clean,  and  free  from  oil  globules.     ■ 
(S.  K.  Alcock.) 

regular  meshwork  of  fibrous  tissue,  in  the  alveoli  of  which  are  masses  of 
multinucleated  protoplasm  (Fig.  270);  numerous  blood-vessels;  and  an 
abundance  of  nervous  elements.     The  cells  are   very  irregular  in  shape 


392  HANDBOOK    OF  PHYSIOLOGY. 

and  size,  poor  in  fat,  and  occasionally  branched;  the  nerves  run  through 
the  cortical  substance,  and  anastomose  over  the  medullary  portion. 

Function. — Of  the  function  of  the  supra-renal  bodies,  nothing  can  be 
definitely  stated,  but  they  are  in  all  probability  connected  with  the 
lymphatic  system. 

Addison's  Disease. — The  collection  of  large  numbers  of  cases  in 
which  the  supra-renal  capsules  have  been  diseased,  has  demonstrated  the 
very  close  relation  subsisting  between  disease  of  those  organs  and  brown 
discoloration  of  the  skin  (Addison's  disease);  but  the  explanation  of  this 
relation  is  still  involved  in  obscurity,  and  consequently  does  not  aid 
much  in  determining  the  functions  of  the  supra-renal  capsules. 

Pituitary  Body. 

This  body  is  a  small  reddish-gray  mass,  occupying  the  sella  turcica 
of  the  sphenoid  bone. 

Structure. — It  consists  of  two  lobes — a  small  posterior  one,  consist- 
ing of  nervous  tissue;  an  anterior  larger  one,  resembling  the  thyroid  in 
structure.  A  canal  lined  with  flattened  or  with  ciliated  epithelium, 
passes  through  the  anterior  lobe;  it  is  connected  with  the  infundibulum. 
The  gland  spaces  are  oval,  nearly  round  at  the  periphery,  spherical  to- 
wards the  centre  of  the  organ;  they  are  filled  with  nucleated  cells  of 
various  sizes  and  shapes  not  unlike  ganglion  cells,  collected  together  into 
rounded  masses,  filling  the  vesicles,  and  contained  in  a  semi-fluid  gran- 
ular substance.  The  vesicles  are  inclosed  by  connective  tissue,  rich  in 
capillaries. 

Function. — Nothing  is  known  of  the  function  of  the  pituitary  body. 

Pineal  Gland. 

This  gland,  which  is  a  small  reddish  body,  is  placed  beneath  the  back 
part  of  the  corpus  callosum,  and  rests  upon  the  corpora  quadrigemina. 

Structure. — It  contains  a  central  cavity  lined  with  ciliated  epithe- 
lium. The  gland  substance  proper  is  divisible  into — (1.)  An  outer  cor- 
tical layer,  analogous  in  structure  to  the  anterior  lobe  of  the  pituitary 
body;  and  (2.)  An  inner  central  layer,  wholly  nervous.  The  cortical 
layer  consists  of  a  number  of  closed  follicles,  containing  (a)  cells  of  va- 
riable shape,  rounded,  elongated,  or  stellate;  (b)  fusiform  cells.  There 
is  also  present  a  gritty  matter  (acervulus  cerebri),  consisting  of  round 
particles  aggregated  into  small  masses.  The  central  substance  consists 
of  white  and  gray  matter.  The  blood-vessels  are  small,  and  form  a  very 
delicate  capillary  plexus. 

Function. — Of  this  there  is  nothing  known. 


THE    VASCULAR   GLANDS.  393 

The  Coccygeal  and  Carotid   Glands. 

These  so-called  glands  are  situated,  the  one  in  front  of  the  tip  of  the 
coccyx,  and  the  other  at  the  point  of  bifurcation  of  the  common  carotid 
artery  on  each  side.  They  are  made  up  of  a  plexus  of  small  arteries, 
are  inclosed  and  supported  by  a  capsule  of  fibrous  tissue,  which  contains 
connective-tissue  corpuscles.  The  blood-vessels  are  surrounded  by  one 
or  more  layers  of  cells  like  secreting-cells,  which  are  said  to  be  modified 
plasma-cells  of  the  connective  tissue.  The  function  of  these  bodies  is 
unknown. 

Functions  of  the  Vascular  Glands  in  General. 

The  opinion  that  the  vascular  glands  serve  for  the  higher  organiza- 
tion of  the  blood,  is  supported  by  their  being  all  especially  active  in  the 
discharge  of  their  functions  during  fcetal  life  and  childhood,  when,  for 
the  development  and  growth  of  the  body,  the  most  abundant  supply  of 
highly  organized  blood  is  necessary.  The  bulk  of  the  thymus  gland,  in 
proportion  to  that  of  the  body,  appears  to  bear  almost  a  direct  propor- 
tion to  the  activity  of  the  body's  development  and  growth,  and  when,  at 
the  period  of  puberty,  the  development  of  the  body  may  be  said  to  be 
complete,  the  gland  wastes,  and  finally  disappears.  The  thyroid  gland 
and  supra-renal  capsules,  also,  though  they  probably  never  cease  to  dis- 
charge some  function,  yet  are  proportionally  much  smaller  in  childhood 
than  in  fcetal  life  and  infancy;  and  with  the  years  advancing  to  the  adult 
period,  they  diminish  yet  more  in  proportionate  size  and  apparent  ac- 
tivity of  function.  The  spleen  more  nearly  retains  its  proportionate 
size,  and  enlarges  nearly  as  the  whole  body  does. 

Although  the  functions  of  all  the  vascular  glands  may  be  similar,  in 
so  far  as  they  may  all  alike  serve  for  the  elaboration  and  maintenance  of 
the  blood,  yet  each  of  them  probably  discharges  a  peculiar  office,  in  re- 
lation either  to  the  whole  economy,  or  to  that  of  some  other  organ. 
Eespecting  any  special  office  of  the  thyroid  gland,  nothing  reasonable 
has  been  hitherto  suggested;  nor  is  there  auy  certain  evidence  concern- 
ing that  of  the  supra-renal  capsules.  Bergman  believed  that  they 
formed  part  of  the  sympathetic  nervous  system  from  the  richness  of 
their  nervous  supply.  Kolliker  looked  upon  the  two  parts  as  function- 
ally distinct,  the  cortical  part  belonging  to  the  blood  vascular  system, 
and  the  medullary  to  the  nervous  svstem. 


CHAPTER  XIV. 

THE    MUSCULAR    SYSTEM. 

I.  Structure  of  Muscular  Tissue. 

There  are  two  chief  kinds  of  muscular  tissue,  differing  both  in 
minute  structure  as  well  as  in  mode  of  action,  viz.  (1.)  the  plain  or  non- 
striated,  and  (2.)  the  striated.  The  striped  form  of  muscular  fibre  is 
sometimes  called  voluntary  muscle,  because  all  muscles  under  the  con- 
trol of  the  will  are  constructed  of  it.  The  plain  or  unstriped  variety  is 
often  termed  involuntary,  because  it  alone  is  found  in  the  greater  num- 
ber of  the  muscles  over  which  the  will  has  no  power. 

(i.)  Unstriped  or  Plain  Muscle. 

Distribution. — Unstriped  muscle  forms  the  proper  muscular  coats 
(1.)  of  the  digestive  canal  from  the  middle  of  the  oesophagus  to  the  in- 


Fig.  271.— Vertical  section  through  the  scalp  with  two  hair  sacs;  a,  epidermis;  b,  cutis;  c,  mus- 
cles of  the  hair-follicles.    (Kolliker. ) 

ternal  sphincter  ani;  (2.)  of  the  ureters  and  urinary  bladder;  (3.)  of  the 
trachea  and  bronchi;  (4.)  of  the  ducts  of  glands;  (5.)  of  the  gall-blad- 
der; (6.)  of  the  vesiculae  seminales;  (7.)  of  the  pregnant  uterus;  (8.)  of 
the  blood-vessels  and  lymphatics;  (9.)  of  the  iris,  and  some  other  parts. 
This  form  of  tissue  also  enters  largely  into  the  composition  (10.)  of  the 
tunica  dartos,  the  contraction  of  which  is  the  principal  cause  of  the 
wrinkling  and  contraction  of  the  scrotum  on  exposure  to  cold.  Un- 
striped muscular  tissue  occurs  largely  also  in  the  cutis  generally,  being 
especially  abundant  in  the  interspaces  between  the  bases  of  the  papillae. 


THE   MUSCULAR    SYSTEM. 


395 


Hence  when  it  contracts  under  the  influence  of  cold,  fear,  electricity,  or 
any  other  stimulus,  the  papillae  are  made  unusually  prominent,  and  give 
rise  to  the  peculiar  roughness  of  the  skin  termed  cutis  anserina,  or 
goose  skin.  It  occurs  also  in  the  superficial  portion  of  the  cutis,  in  all 
parts  where  hairs  occur,  in  the  form  of  flattened  roundish  bundles,  which 
lie  alongside  the  hair-follicles  and  sebaceous  glands.     They  pass  obliquely 


Fig.  272.— A,  unstriped  muscle  cells  from  the  mesentery  of  a  newt.  The  sheath  exhibits  trans- 
verse markings,  x  180.  B,  from  a  similar  preparation,  showing  that  each  muscle  cell  consists  of  a 
central  bundle  of  fibrils,  F  (contractile  part),  connected  with  the  intra-nuclear  network,  N,  and  a 
sheath  with  annular  thickenings,  St.  The  cells  show  varicosities  due  to  local  contraction  and  on 
these  the  annular  thickenings  are  most  marked.    X  460.    (FJein  and  Noble  Smith.) 

from  without  inwards,  embrace  the  sebaceous  glands,  and  are  attached  to 
the  hair-follicles  near  their  base  (Fig.  271). 

Structure. — Unstriated  muscles  are  made  up  of  elongated,  spindle- 


Fig.  273.— Plexus  of  bundles  of  unstriped  muscle  cells  from  the  pulmonary  pleura  of  the  guinea- 
pig.     X  180.    (Klein  and  Noble  Smith.)    A,  branching  fibres;  B,  their  long  central  nuclei. 

shaped,  nucleated  cells  (Fig.  272),  which  in  their  perfect  form  are  flat, 
from  about  j^Vtt  to  g-gVir  °^  an  iQCn  broad,  and  -^\s  to  ^^  of  an  inch  in 
length — very  clear,  granular,  and  brittle,  so  that  when  they  break  they 
often  have  abruptly  rounded  or  square  extremities.  Each  cell  of  these 
consists  of  a  fine  sheath,  probably  elastic;  of  a  central  bundle  of  fibrils 
representing  the  contractile  substance;  and  of  an  oblong  nucleus,  which 


396 


HANDBOOK    OF    PHYSIOLOGY. 


includes  within  a  membrane  a  fine  network  anastomosing  at  the  poles  of 
the  nucleus  with  the  contractile  fibrils.  The  ends  of  fibres  are  usually 
single,  sometimes  divided.  Between  the  fibres  is  an  albuminous  cementing 
material  or  endomysium  in  which  are  found  connective-tissue  corpuscles, 
and  a  few  fibres.  The  perimysium  is  continuous  with  the  endomysium 
in  the  fibrous  connective  tissue  surrounding  and  separating  the  bundles 
of  muscle  cells. 

(2.)  Striated  or  Striped  Muscles. 

Distribution. — The  striated  muscles  include  the  whole  of  the  volun- 
tary muscles  of  the  body,  the  heart,  and  those  muscles  neither  completely 
voluntary  nor  involuntary,  which  form  part  of  the  walls  of  the  pharynx, 
and  exist  in  certain  other  parts  of  the  body,  as  the  internal  ear,  urethra, 
etc. 

Structure. — All  these  muscles  are  composed  of  fleshy  bundles  called 
fasciculi,  inclosed  in  coverings  of  fibro-cellular  tissue  or  perimysium,  by 


Fig.  274. 


Fig.  275. 


Fig.  274.— A  small  portion  of  muscle  natural  size,  consisting  of  larger  and  smaller  fasciculi,  seen 
in  a  transverse  section,  and  a.  the  same  magnified  5  diameters.    (Sharpey.) 

Fig.  275.— Muscular  fibre  torn  across;  the  sarcolemma  still  connecting  the  two  parts  of  the 
fibre.    (Todd  and  Bowman.) 

which  each  is  at  once  connected  with  and  isolated  from  those  adjacent  to 
it  (Fig.  274).  Each  fasciculus  is  made  up  of  several  smaller  bundles, 
similarly  ensheathed.  A  bundle  is  made  up  of  muscle  fibres  with  small 
processes  and  connective-tissue  cells  between  them  or  endomysium. 

Each  muscular  fibre  is  thus  constructed: — Externally  is  a  fine,  trans- 
parent, structureless  membrane,  called  the  sarcolemma,  which  in  the 
form  of  a  tubular  investing  sheath  forms  the  outer  wall  of  the  fibre,  and 
is  filled  up  by  the  contractile  material  of  which  the  fibre  is  chiefly  made 
np.  Sometimes,  from  its  comparative  toughness,  the  sarcolemma  will 
remain  untorn,  when  by  extension  the  contained  part  can  be  broken 
(Fig.  275),  and  its  presence  is  in  this  way  best  demonstrated.  The 
fibres,  which  are  cylindriform  or  prismatic,  with  an  average  diameter  of 
about  -ji^  of  an  inch,  are  of  a  pale  yellow  color,  and  apparently  marked 
by  fine  stria?,  which  pass  transversely  round  them,  in  slightly  curved  or 


THE    MUSCULAR    SYSTEM. 


o  J  i 


wholly  parallel  lines.  Each  fibre  is  found  to  consist  of  broad  dim  bands 
of  highly  refractive  substance  representing  the  contractile  portion  of  the 
muscle  fibre— the  contractile  discs— alternating  with  narrow  bright  bands 
of  a  less  refractive  substance  —the  interstitial  discs.  After  hardening, 
each  contractile  disc  becomes  longitudinally  striated,  the  thin  oblong 
rods  thus  formed  being  the  sarcous  elements  of  Bowman.  The  sarcous 
elements  are  not  the  optical  units,  since  each  consists  of  minute  doubly- 
refracting  elements— the  disdiaclasts  of  Brucke.  When  seen  in  trans- 
verse section  the  contractile  discs  appear  to  be  subdivided  by  clear  lines 
into  polygonal  areas  Cohnheim's  fields  (Fig.  278),  each  corresponding  to 
one  sarcous  element  prism.     The  clear  lines  are  due  to  a  transparent  in- 


FIQ.  276. 


Fig.  277. 


Fig.  276.  Part  of  a  striped  muscle-fibre  of  a  water  beetle  prepared  with  absolute  alcohol.  A, 
sarcolemma;  B.  Krause's  membrance.  The  sarcolemma  shows  regular  bulgings.  Above  and  below 
Krause's  membrane  are  seen  the  transparent  "  lateral  discs."  The  chief  mass  of  a  muscular  com- 
partment is  occupied  by  the  contractile  disc  composed  of  sarcous  elements.  The  substance  of  the 
individual  sarcous  elements  has  collected  more  at  the  extremity  than  in  the  centre:  hence  this  latter 
is  more  transparent.  The  optical  effect  of  this  is  that  the  contractile  disc  appears  to  possess  a 
"  median  disc  "  (Disc  of  Hensen).  Several  nuclei  of  muscle  corpuscles,  C  and  D,  are  shown,  and  in 
them  a  minute  network.     X  300.    (Klein  and  Noble  Smith.) 

Fig.  277.  A.  Portion  of  a  medium-sized  human  muscular  fibre.  X  800.  B.  Separated  bundles 
of  fibrils  equally  magnified ;  a,  a,  larger,  and  b,  b,  smaller  collections;  c,  still  smaller;  d,  d,  the 
smallest  which  could  be  detached,  possibly  representing  a  single  series  of  sarcous  elements. 
(Sharpey.) 

terstitial  fluid  substance  pressed  out  of  the  sarcous  elements  when  they 
coagulate.  The  sarcolemma  is  a  transparent  structureless  elastic  sheath 
of  great  resistance  which  surrounds  each  fibre  (Fig.  275).  There  is  still 
some  doubt  regarding  the  nature  of  the  fibrils.  Each  of  them  appears 
to  be  composed  of  a  single  row  of  minute  dark  quadrangular  particles, 
called  sarcous  elements,  which  are  separated  from  each  other  by  a  bright 


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HANDBOOK    OF   PHYSIOLOGY. 


space  formed  of  a  pellucid  substance  continuous  with  them.  According 
to  Sharpey,  even  in  a  fibril  so  constituted,  the  ultimate  anatomical  ele- 
ments of  the  fibre  are  not  isolated.  His  view  was  that  each  fibril  with 
quadrangular  sarcous  elements  is  composed  of  a  number  of  other  fibrils 
still  finer,  so  that  the  sarcous  element  of  an  ultimate  fibril  would  be 
not  quadrangular  but  as  a  streak.  In  either  case  the  appearance  of 
striation  in  the  whole  fibre  would  be  produced  by  the  arrangement, 
side  by  side,  of  the  dark  and  light  portions  respectively  of  the  fibrils 
(Fig.  277). 

A  fine  black  streak  can  usually  be  discerned  passing  across  the  inter- 
stitial disc  between  the  sarcous  elements:  this  streak  is  termed  Krause's 
membrane:  it  is  continuous  at  each  end  with  the  sarcolemma  investing 
the  muscular  fibre  (Fig.  276  B). 

Thus  the  space  inclosed  by  the  sarcolemma  is  divided  into  a  series  of 
compartments  by  the  transverse   partitions  known  as  Krause's  mem- 


Fiq.  278.  Fig.  279. 

Fig.  278.— Three  muscular  fibres  running  longitudinally,  and  two  bundles  of  fibres  in  transverse 
section,  M,  from  the  tongue.    The  capillaries,  C,  are  injected,    x  150.    (Klein  and  Noble  Smith.) 

Fig.  279.  —Transverse  section  through  muscular  fibres  of  human  tongue.  The  muscle-corpuscles 
are  indicated  by  their  deeply-stained  nuclei  situated  at  the  inside  of  the  sarcolemma.  Each  muscle- 
fibre  shows  the  "  Cohnheim's  fields,"  that  is,  the  sarcous  elements  in  transverse  section  separated 
by  clear  (apparently  linear)  interstitial  substance,    x  450.    (Klein  and  Noble  Smith.) 

Cranes;  these  compartments  being  occupied  by  the  true  muscle  substance. 
On  each  side  (above  and  below)  of  this  membrane  is  a  bright  border 
(lateral  disc).  In  the  centre  of  the  dark  zone  of  sarcous  elements  a 
lighter  band  can  sometimes  be  dimly  discerned:  this  is  termed  the  middle 
disc  of  Hensen  (see  Fig.  276,  A). 

In  some  fibres,  chiefly  those  from  insects,  each  lateral  disc  contains  a 
row  of  bright  granules  forming  the  granular  layer  of  Flogel.  The 
fibres  contain  nuclei,  which  are  roundish  ovoid,  or  spindle-shaped  in 
different  animals.  These  nuclei  are  situated  close  to  the  sarcolemma, 
their  long  axes  being  parallel  to  the  fibres  which  contain  them.  Each 
nucleus  is  composed  of  a  uniform  network  of  fibrils,  and  is  imbedded  in 
a  thin,  more  or  less  branched  film  of  protoplasm.  The  nucleus  and  pro- 
toplasm together  form  the  muscle  cell  or  muscle-corpuscle  of  Max 
£>chultze. 


THE    MUSCULAK    SYSTEM.  399 

The  sarcous  elements  and  Krause's  membranes  are  doubly  refracting, 
the  rest  of  the  fibre  singly  refracting.     (Briicke.) 

According  to  Schafer,  the  granules,  which  have  been  mentioned  on 
either  side  of  Krause's  membrane,  are  little  knobs  attached  to  the  ends 
of  "  muscle-rods;"  and  these  muscle-rods,  knobbed  at  each  end,  and  im- 
bedded in  a  homogeneous  protoplasmic  ground-substance,  form  the  sub- 
stance of  the  muscles.  This  view  of  the  structure  of  muscle  requires 
further  confirmation. 

Although  each  muscular  fibre  may  be  considered  to  be  formed  of  a 
number  of  longitudinal  fibrils,  arranged  side  by  side,  it  is  also  true  that 
they  are  not  naturally  separate  from  each  other,  there  being  lateral  cohe- 
sion, if  not  fusion,  of  each  sarcous  element  with  those  around  and  in  con- 
tact with  it;  so  that  it  happens  that  there  is  a  tendency  for  a  fibre  to 
split,  not  only  into  separate  fibrils,  but  also  occasionally  into  plates  or 


I 


Fig.  280. — From  a  preparation  of  the  nerve-termination  in  the  muscular  fibres  of  a  snake,  a. 
End  plate  seen  only  broad  surfaced,    b,  End  plate  seen  as  narrow  surface.    (Lingard  and  Klein.  | 

discs,  each  of  which  is  composed  of  sarcous  elements  laterally  adherent 
one  to  another. 

Muscular  Fibres  of  the  Heart  (Figs.  92  and  93)  form  the  chief, 
though  not  the  only  exception  to  the  rule,  that  involuntary  muscles  are 
constructed  of  plain  fibres;  but  although  striated  and  so  far  resembling 
those  of  the  voluntary  muscles,  they  present  these  distinctions: — Each 
muscular  fibre  is  made  up  of  elongated,  nucleated,  and  branched  cells, 
the  nuclei  or  muscle-corpuscles  being  centrally  placed  in  the  fibre.  The 
fibres  are  finer  and  less  distinctly  striated  than  those  of  the  voluntary 
muscles;  and  no  sarcolemma  can  be  usually  discerned. 

Blood  and  Nerve  Supply. — The  voluntary  muscles  are  freely  supplied 
with  blood-vessels;  the  capillaries  form  a  network  with  oblong  meshes 
around  the  fibres  on  the  outside  of  the  sarcolemma.  No  vessels  pene- 
trate the  sarcolemma  to  enter  the  interior  of  the  fibre.  Nerves  also  are 
supplied  freely  to  muscles;  the  voluntary  muscles  receiving  them  from 


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HANDBOOK    OF    PHYSIOLOGY. 


the  cerebro-spinal  system,  and  the  unstriped  muscles  from  the  sympa- 
thetic or  ganglionic  system. 

The  nerves  terminate  in  the  muscular  fibre  in  the  following  ways: — 
(1.)  In  xmstriped  muscle,  the  nerves  first  of  all  form  a  plexus,  called  the 
ground  plexus  (Arnold),  corresponding  to  each  group  of  muscle  bun- 
dles; the  plexus  is  made  by  the  anastomosis  of  the  primitive  fibrils  of 
the  axis-cylinders.  From  the  ground  plexus,  branches  pass  of,  and 
again  anastomosing,   form  plexuses  which  correspond  to  each  muscle 


Fig.  281— Two  striped  muscle-fibres  of  the  hyoglossus  of  frog,  a,  Nerve  end-plate ;  b,  nerve- 
fibres  leaving  the  end-plate;  c,  nerve-fibres,  terminating  after  dividing  into  branches  d,  a  nucleus  in 
which  two  nerve-fibres  anastomose.     X  600.     (Arndt .) 

bundle — intermediary  plexuses.  From  these  plexuses  branches  consist- 
ing of  primitive  fibrils  pass  in  between  the  individual  fibres  and  anasto- 
mose. These  fibrils  either  send  off  finer  branches,  or  terminate  them- 
selves in  the  nuclei  of  the  muscle  cells. 

(2.)  In  striped  muscle  the  nerves  end  in  motorial  end-plates,  having 
first  formed,  as  in  the  case  of  unstriped  fibres,  ground  and  intermediary 
plexuses.     The  fibres  are,  however,  medullated,  and  when  a  branch  of 


THE    MUSCULAK    SYSTEM.  401 

the  intermediary  plexus  passes  to  enter  a  muscle- fibre,  its  primitive 
sheath  becomes  continuous  with  the  sarcolemma,  and  the  axis-cylinder 
forms  a  network  of  its  fibrils  on  the  surface  of  the  fibre.  This  network 
lies  imbedded  in  a  flattened  granular  mass  containing  nuclei  of  several 
kinds;  this  is  the  motorial  end-plate  (Fig.  281).  In  batrachia,  besides 
end-plates,  there  is  another  way  in  which  the  nerves  end  in  the  muscle- 
fibres,  viz.,  by  rounded  extremities,  to  which  oblong  nuclei  are  attached. 

Development. — (1.)  Unstriped. — The  cells  of  unstriped  muscle  are 
derived  directly  from  embryonic  cells,  by  an  elongation  of  the  cell,  and 
its  nucleus;  the  latter  changing  from  a  vesicular  to  a  rod  shape. 

(2.)  Striped. — Formerly  it  was  supposed  that  striated  fibres  were 
formed  by  the  coalescence  of  several  cells,  but  recently  it  has  been  proved, 
that  each  fibre  is  formed  from  a  single  cell,  the  process  involving  an  enor- 
mous increase  in  size,  a  multiplication  of  the  nucleus  by  fission,  and  a 
differentiation  of  the  cell-contents.  This  view  differs  but  little  from  the 
other,  that  the  muscular  fibres  is  produced,  not  by  multiplication  of 
cells,  but  by  arrangement  of  nuclei  in  a  growing  mass  of  protoplasm 
(answering  to  the  cell  in  the  theory  just  referred  to),  which  becomes 
gradually  differentiated  so  as  to  assume  the  characters  of  a  fully  devel- 
oped muscular  fibre. 

Growth  of  Muscle.— The  growth  of  muscles  both  striated  and  non- 
striated,  is  the  result  of  an  increase  both  in  the  number  and  size  of  the 
individual  elements.  In  the  pregnant  uterus  the  fibre  cells  may  become 
enlarged  to  ten  times  their  original  length.  In  involution  of  the  uterus 
after  parturition  the  reverse  changes  occur,  accompanied  generally  by 
some  fatty  infiltration  of  the  tissue  and  degeneration  of  the  fibres. 

II.  The  Chemical  Composition"  of  Muscle. 

A.  Proteids. — The  principal  substance  which  can  be  extracted  from 
muscle,  when  examined  after  death,  is  a  proteid  body,  called  Myosin. 
This  body  appears  to  bear  the  same  relation  to  the  living  muscle,  as 
fibrin  does  to  the  living  blood,  since  the  coagulation  of  muscle  after  death 
is  due  to  the  formation  of  myosin.  Thus  if  coagulation  be  delayed  in 
muscles  removed  immediately  from  recently  killed  animals,  by  subjecting 
them  to  a  temperature  below  0°  C,  it  is  possible  to  obtain  from  them  by 
expression  a  viscid  fluid  of  slightly  alkaline  reaction,  called  muscle  plasma, 
(Kuhne,Halliburton).  And  muscle  plasma,  if  exposed  to  the  ordinary 
temperature  of  the  air  (and  more  quickly  at  37-40°  C),  undergoes  coag- 
ulation much  in  the  same  way  as  does  blood  plasma,  separated  from  the 
blood  by  the  action  of  a  low  temperature,  under  similar  circumstances. 
The  appearances  presented  by  the  fluid  during  the  process  are  also  very 
similar  to  the  phenomena  of  blood-clotting,  viz.,  that  first  of  all  an  in- 
creased viscidity  on  the  surface  of  the  fluid,  and  at  the  sides  of  the  con- 
taining vessel,  appears,  which  gradually  extends  throughout  the  entire 
mass,  until  a  fine  transparent  clot  is    obtained.     In  the  course  of  some 

hours  the  clot  begins  to  contract,  and  to  squeeze  out  of  its  meshes  a  fluid 
36 


402  HANDBOOK    OF    PHYSIOLOGY. 

corresponding  to  blood-serum.  In  the  course  of  coagulation,  therefore, 
muscle  plasma  separates  into  muscle  clot  and  muscle  serum.  The  mus- 
cle clot  is  the  substance  myosin.  It  differs  from  fibrin  in  being  easily 
soluble  in  a  2  per  cent  solution  of  hydrochloric  acid,  and  a  10  per  cent 
solution  of  sodium  chloride.  It  is  insoluble  in  distilled  water,  and  its 
solutions  coagulate  on  application  of  heat.  It  is  a  body,  therefore, 
belonging  to  the  globulin  class  of  proteids.  During  the  process  the  re- 
action of  the  fluid  becomes  distinctly  acid. 

The  coagulation  of  muscle  plasma  can  not  only  be  prevented  by  cold, 
but  also,  as  Halliburton  has  shown,  by  the  presence  of  neutral  salts  in 
certain  proportions;  for  example,  of  sodium  chloride,  of  magnesium  sul- 
phate, or  of  sodium  sulphate.  It  will  be  remembered  that  this  is  also 
the  case  with  blood  plasma.  Dilution  of  the  salted  muscle  plasma  will 
produce  its  slow  coagulation,  which  is  prevented  by  the  presence  of  neu- 
tral salts  if  in  strong  solution. 

It  is  highly  probable  that  the  formation  of  muscle-clot  is  a  ferment 
action  {myosin  ferment).  The  antecedent  of  myosin  in  living  muscle 
has  received  the  name  of  myosinogen,  in  the  same  way  as  the  fibrin- 
forming  element  in  the  blood  is  called  fibrinogen.  Myosinogen  is,  how- 
ever, made  up  of  two  globulins,  which  coagulate  at  the  temperatures 
47°  C.  and  56°  C.  respectively.  Myosin  may  also  be  obtained  from  dead 
muscle  by  subjecting  it,  after  all  the  blood,  fat,  and  fibrous  tissue,  and 
substances  soluble  in  water  have  been  removed,  to  a  10  per  cent  solution 
of  sodium  chloride,  or  5  per  cent  solution  of  magnesium  sulphate,  or  10 
to  15  per  cent  solution  of  ammonium  chloride,  filtering  and  allowing  the 
filtrate  to  drop  into  a  large  quantity  of  water,  when  myosin  separates  out 
as  a  white  flocculent  precipitate. 

A  very  remarkable  fact  with  regard  to  the  properties  of  myosin  has 
been  demonstrated  by  Halliburton,  namely,  that  a  solution  of  muscle 
which  has  undergone  rigor  mortis,  in  strong  neutral  saline  solution,  pos- 
sesses very  much  the  same  properties  as  muscle  plasma,  and  that  if  di- 
luted with  twice  or  three  times  its  bulk  of  water,  myosin  will  separate 
out  as  a  clot,  which  clot  can  be  again  dissolved  in  a  strong  neutral  saline 
solution,  and  the  solution  can  be  again  made  to  clot  on  dilution.  This 
process  can  be  often  repeated;  but  in  the  fluid  which  exudes  from  the 
clot  there  is  no  proteid  present.  Myosin  then  when  dissolved  in  neutral 
saline  fluids  is  converted  into  myosinogen,  but  reappears  on  dilution  of 
the  fluid. 

Muscle  clot  is  almost  pure  myosin;  but  it  appears  to  be  combined 
with  a  certain  amount  of  salts,  for  if  it  be  freed  from  salts,  especially  of 
those  of  calcium,  by  prolonged  dialysis,  it  loses  its  solubility.  If  a  small 
amount  of  calcium  salts  be  added,  however,  it  regains  that  property. 

Muscle  serum  is  acid  in  reaction,  and  almost  colorless.  It  contains 
three  proteid  bodies,  viz. — (a.)  A  globulin  {myo-globulin),  which  can  be 


I'HE    MUSCULAE    SYSTEM.  403 

precipitated  by  saturation  with  sodium  chloride,  or  magnesium  sulphate, 
and  which  can  be  coagulated  at  G3°  C.  (b.)  Serum-albumin,  which 
coagulates  at  73°  C,  but  is  not  precipitated  by  saturation  with  either  of 
those  salts.  And  (c.)  Myo-albumin,  which  is  neither  precipitated  by 
heat,  nor  by  saturation  with  sodium  chloride  or  magnesium  sulphate, 
but  may  be  by  saturation  with  ammonium  sulphate.  It  is  closely  con- 
nected with,  even  if  it  is  not  itself,  myosin  ferment.  Xeither  casein  nor 
peptone  has  been  found  by  Halliburton  in  muscle  extracts.  In  extracts 
of  muscles,  especially  of  red  muscles,  there  is  a  certain  amount  of  ffce- 
moglobin,  and  also  of  a  pigment  special  to  muscle,  called  by  McMunn 
Mijo-hcematin,  which  has  a  spectrum  quite  distinct  from  haemoglobin, 
viz.,  a  narrow  baud  just  before  D,  two  very  narrow  between  D  and  E, 
and  two  other  faint  bands,  near  the  violet,  E  b,  and  between  E  and  F 
close  to  P  (McMunn). 

B.  Ferments. — In  addition  to  muscle  ferments,  already  mentioned, 
muscle  extracts  contain  certain  small  amounts  oi  pepsin  and  fibrin  fer- 
ment, and  also  of  an  amyloly  tic  ferment. 

C.  Acids,  particularly  sarco-lactic,  also  acetic  and  formic. 

D.  Glycogen  and  Glucose,  also  Inosite. 

E.  Nitrogenous  crystalline  bodies,  such  as  Kreatin,  Hypoxanthin, 
or  carnin,  Taurin  and  Urea,  the  last  in  very  small  amount. 

F.  Salts,  the  chief  of  which  is  potassium  phosphate. 

III.  Physiology  of  Muscle. 

Muscle  may  exist  in  three  different  conditions:  A.  during  rest;  B. 
during  activity;  and  C.  in  rigor. 

A.  Rest. 

Physical  condition. — During  rest  or  inactivity  a  muscle  has  a  slight 
but  very  perfect  Elasticity;  it  admits  of  being- considerably  stretched  ; 
but  returns  readily  and  completely  to  its  normal  condition.  In  the  liv- 
ing body  the  muscles  are  always  stretched  somewhat  beyond  their  natural 
length;  they  are  always  in  a  condition  of  slight  tension;  an  arrangement 
which  enables  the  whole  force  of  the  contraction  to  be  utilized  in  ap- 
proximating the  points  of  attachment.  It  is  obvious  that  if  the  muscles 
were  lax,  the  first  part  of  the  contraction  until  the  muscle  became  tight 
would  be  wasted. 

There  is  no  doubt  that  even  in  a  condition  of  rest  Oxygen  is  abstract- 
ed from  the  blood,  and  carbonic  acid  is  given  out  by  a  muscle;  for  the 
blood  becomes  venous  in  the  transit,  and  since  the  muscles  form  by  far 
the  largest  element  in  the  composition  of  the  body,  chemical  changes 
must  be  constantly  going  on  in  them  as  in  other  tissues  and  organs,  al- 
though not  necessarily  accompanied   by  contraction.     When  cut  out  of 


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HANDBOOK    OF   PHYSIOLOGY. 


the  body  such  muscles  retain  their  contractility  longer  in  an  atmosphere 
of  oxygen  than  in  an  atmosphere  of  hydrogen  or  carbonic  acid,  and  dur- 
ing life,  an  amount  of  oxygen  is  no  doubt  necessary  to  the  manifestation 
of  energy  as  well  as  for  the  metabolism  going  on  in  the  resting  condi- 
tion. 

The  reaction  of  living  muscle  in  a  resting  or  inactive  condition  is 
neutral  or  faintly  alkaline. 

In  muscles  which  have  been  removed  from  the  body,  it  has  been 
found  that  for  some  little  time  electrical  currents  can  be  demonstrated 
passing  from  point  to  point  on  their  surface;  but  as  soon  as  the  muscles 
die  or  enter  into  rigor  mortis,  these  currents  disappear. 

The  Method  of  Demonstration  usually  employed  is  as  follows: — 
The  frog's  muscles  are  the  most  convenient  for  experiment;  and  a  muscle 
of  regular  shape,  in  which  the  fibres  are  parallel,  is  selected.     The  ends 


Fig.  282.— Diagram  of  Du  Bois  Reymond's  non-polarizable  electrodes,  a,  glass  tube  filled  with 
a  saturated  solution  of  zinc  sulphate,  in  the  end,  c,  of  which  is  china  clay  drawn  out  to  a  point;  in 
the  solution  a  well  amalgamated  zinc  rod  is  immersed  and  connected,  by  means  of  the  wire  which 
passes  through  a,  with  the  galvanometer.  The  remainder  of  the  apparatus  is  simply  for  conveni- 
ence of  application.    The  muscle  and  the  end  of  the  second  electrode  are  to  the  right  of  the  figure. 

are  cut  off  by  clean  vertical  cuts,  and  the  resulting  piece  of  muscle  is 
called  a  regular  muscle  prism.  The  muscle  prism  is  insulated,  and  a 
pair  of  non-polarizable  electrodes  connected  with  a  very  delicate  galva- 
nometer is  applied  to  various  points  of  the  prism,  and  by  a  deflection  of 
the  needle  to  a  greater  or  less  extent  in  one  direction  or  another,  the 
strength  and  direction  of  the  currents  in  the  piece  of  muscle  can  be  esti- 
mated. It  is  necessary  to  use  non-polarizable  and  not  metallic  electrodes 
in  this  experiment,  as  otherwise  there  is  no  certainty  that  the  whole  of 
the  current  observed  is  communicated  from  the  muscle  itself,  and  is  not 
derived  from  the  metallic  electrodes,  in  consequence  of  the  action  of  the 
saline  juices  of  the  tissues  upon  them.  The  form  of  the  non-polarizable 
electrodes  is  a  modification  of  du  Bois  Eeymond's  apparatus  (Fig.  282), 
which  consists  of  a  somewhat  flattened  glass  cylinder  a,  drawn  abruptly 
to  a  point,  and  fitted  to  a  socket  capable  of  movement,  and  attached  to 
a  stand  A,  so  that  it  can  be  raised  or  lowered  as  required.  The  lower 
portion  of  the  cylinder  is  filled  with  china  clay  moistened  with  saline  so- 


THE    MUSCULAR.  SYSTEM. 


405 


lution,  part  of  which  projects  through  its  drawn-out  point;  the  rest  of 
the  cylinder  is  fitted  with  a  saturated  solution  of  zincsulphateinto  which 
dips  a  well  amalgamated  piece  of  zinc  which  is  connected  by  means  of  a 
wire  with  the  galvanometer.  In  this  way  the  zinc  sulphate  forms  a 
homogeneous  and  non-polarizable  conductor  between  the  zinc  and  the 
china  clay.  A  second  electrode  of  the  same  kind  is,  of  course,  neces- 
sary. 

In  a  regular  muscle  prism  the  currents  are  found  to  be  as  follows: — 
If  from  a  point  on  the  surface  a  line — the  equator — be  drawn  across 
the  muscle  prism  equally  dividing  it,  currents  pass  from  this  point  to 
points  away  from  it,  which  are  weak  if  the  points  are  near,  and  increase 
in  strengtb  as  the  points  are  further  and  further  away  from  the  equator; 
the  strongest  passing  from  the  equator  to  a  point  representing  the  mid- 
dle of  the  cut  ends  (Fig.  283,  2);  currents  also  pass  from  points  nearer 
the  equator  to  those  more  remote  (Fig.  283,  1,  3,  4),  but  not  from  points 
equally  distant,  or  isoelectric  points  (Fig.  283,  6,  7,  8).     The  cut  ends 


Fig.  233.—  Diagram  of  the  currents  in  a  muscle  prism.    (Du  Bois  Reymond.) 


are  always  negative  to  the  equator.  These  currents  are  constant  for 
some  time  after  removal  of  the  muscle  from  the  body,  and  in  fact  re- 
main as  long  as  the  muscle  retains  its  life.  They  are  in  all  probability 
due  to  chemical  changes  going  on  in  the  muscles. 

The  currents  are  diminished  by  fatigue  and  are  increased  by  an  in- 
crease of  temperature  within  natural  limits.  If  the  uninjured  tendon 
be  used  as  the  end  of  the  muscle,  and  the  muscle  be  examined  without 
removal  from  the  body,  the  currents  are  very  feeble,  but  they  are  at 
once  much  increased  by  injuring  the  muscle,  as  by  cutting  off  its  tendon. 
The  last  observation  appears  to  show  that  they  are  right  who  believe  that 
the  currents  do  not  exist  in  muscles  uninjured  in  situ,  but  that  injury, 
either  mechanical,  chemical  or  thermal,  will  render  the  injured  part 
electrically  negative  to  other  points  on  the  muscle.  In  a  frog's  heart  it 
has  been  shown,  too,  that  no  currents  exist  during  its  inactivity,  but 
that  as  soon  as  it  is  injured  in  any  way  they  are  developed;  the  injured 
part  being  negative  to  the  rest  of  the  muscle.     The  currents  which  have 


406  HANDBOOK    OF    PHYSIOLOGY. 

been  above  described  are  called  either  natural  muscle  currents  or  cur- 
rents of  rest,  according  as  they  are  looked  upon  as  always  existing  in 
muscle  or  as  developed  when  a  part  of  the  muscle  is  subjected  to  injury; 
in  either  case,  up  to  a  certain  point,  it  is  agreed  that  the  strength  of  the 
currents  is  in  direct  proportion  to  the  injury. 

B.   Activity. 

The  property  of  muscular  tissue,  by  which  its  peculiar  functions 
are  exercised,  is  its  Contractility,  which  is  excited  by  all  kinds  of 
stimuli  applied  either  directly  to  the  muscles,  or  indirectly  to  them 
through  the  medium  of  their  motor  nerves.  This  property,  although 
commonly  brought  into  action  through  the  nervous  system,  is  inherent 
in  the  muscular  tissue.  For — (1.)  it  may  be  manifested  in  a  muscle 
which  is  isolated  from  the  influence  of  the  nervous  system  by  division 
of  the  nerves  supplying  it,  so  long  as  the  natural  tissue  of  the  muscle  is 
duly  nourished;  and  (2.)  it  is  manifest  in  a  portion  of  muscular  fibre,  in 
which,  under  the  microscope,  no  nerve-fibre  can  be  traced.  (3.)  Sub- 
stances such  as  urari,  which  paralyze  the  nerve-endings  in  muscles,  do 
not  at  all  diminish  the  irritability  of  the  muscle.  (4.)  When  a  muscle 
is  fatigued,  a  local  stimulation  is  followed  by  a  contraction  of  a  small 
part  of  the  fibre  in  the  immediate  vicinity  without  any  regard  to  the  dis- 
tribution of  nerve-fibres. 

If  the  removal  of  nervous  influence  be  long  continued,  as  by  division 
of  the  nerves  supplying  a  muscle,  or  in  cases  of  paralysis  of  long-stand- 
ing, the  irritability,  i.  e.,  the  power  of  both  perceiving  and  responding 
to  a  stimulus,  may  be  lost;  but  probably  this  is  chiefly  due  to  the  im- 
paired nutrition  of  the  muscular  tissue,  which  ensues  through  its  inac- 
tion. The  irritability  of  muscles  is  also  of  course  soon  lost,  unless  a 
supply  of  arterial  blood  to  them  is  kept  up.  Thus,  after  ligature  of  the 
main  arterial  trunk  of  a  limb,  the  power  of  moving  the  muscles  is  par- 
tially or  wholly  lost,  until  the  collateral  circulation  is  established;  and 
when,  in  animals,  the  abdominal  aorta  is  tied,  the  hind  legs  are  ren- 
dered almost  powerless. 

The  same  fact  may  be  readily  shown  by  compressing  the  abdominal 
aorta  in  a  rabbit  for  about  10  minutes;  if  the  pressure  be  released  and 
the  animal  be  placed  on  the  ground,  it  will  work  itself  along  with  its 
front  legs,  while  the  hind  legs  sprawl  helplessly  behind.  Gradually  the 
muscles  recover  their  power  and  become  quite  as  efficient  as  before. 

So,  also,  it  is  to  the  imperfect  supply  of  arterial  blood  to  the  muscu- 
lar tissue  of  the  heart,  that  the  cessation  of  the  action  of  this  organ  in 
asphyxia  is  in  some  measure  due. 

Besides  the  property  of  contractility,  the  muscles,  especially  the 
striated,  possess  Sensibility  by  means  of  the  sensory  nerve-fibres  distrib- 


THE   MUSCULAR    SYSTEM.  407 

uted  to  them.  The  amount  of  common  sensibility  in  muscles  is  not 
great;  for  they  maybe  cut  or  pricked  without  giving  rise  to  severe  pain, 
at  least  in  their  healthy  condition.  But  they  have  a  peculiar  sensibility, 
or  at  least  a  peculiar  modification  of  common  sensibility,  which  is  shown 
in  that  their  nerves  can  communicate  to  the  mind  an  accurate  knowl- 
edge of  their  states  and  positions  when  in  action.  By  this  sensibility  we 
are  not  only  made  conscious  of  the  morbid  sensations  of  fatigue  and 
cramp  in  muscles,  but  acquire,  through  muscular  action,  a  knowledge 
of  the  distance  of  bodies  and  their  relation  to  each  other,  and  are  en- 
abled to  estimate  and  compare  their  weight  and  resistance  by  the  effort 
of  which  we  are  conscious  in  measuring,  moving,  or  raising  them. 

The  Phenomena  of  Muscular  Contraction. 

The  power  which  muscles  possess  of  contraction  may  then  be  called 
forth  by  stimuli  of  various  kinds,  and  these  stimuli  may  also  be  applied 
directly  to  the  muscle  or  indirectly  to  the  nerve  supplying  it.  There 
are  distinct  advantages,  however,  in  applying  the  stimulus  through  the 
nerves,  as  it  is  more  convenient,  as  well  as  more  potent.  The  stimuli 
are  of  four  kinds,  viz. : — 

(1.)  Mechanical  stimuli,  as  by  a  blow,  pinch,  prick  of  the  muscle  or 
its  nerves,  will  produce  a  contraction,  repeated  on  the  repetition  of  the 
stimulus;  but  if  applied  to  the  same  point  for  a  limited  number  of  times 
only,  as  such  stimuli  will  soon  destroy  the  irritability  of  the  preparation. 

(2.)  TJiermal  stimuli. — If  a  needle  be  heated  and  applied  to  a  muscle 
or  its  nerve,  the  muscle  will  contract.  A  temperature  of  over  100°  F. 
(37.8°  C.)  will  cause  the  muscles  of  a  frog  to  pass  into  a  condition 
known  as  heat  rigor. 

(3.)  Chemical  stimuli. — A  great  variety  of  chemical  substances  will 
3xcite  the  contraction  of  muscles,  some  substances  being  more  potent  in 
irritating  the  muscle  itself,  and  other  substances  having  more  effect  upon 
the  nerve.  Of  the  former  may  be  mentioned,  dilute  acids,  salts  of  cer- 
tain metals,  e.  g.,  zinc,  copper  and  iron;  to  the  latter  belong  strong 
glycerin,  strong  acids,  ammonia  and  bile  salts  in  strong  solution. 

(4.)  Electrical  Stimuli. — For  the  purpose  of  experiment  electrical 
stimuli  are  most  frequently  used,  as  the  strength  of  the  stimulus  may  be 
more  conveniently  regulated.  Any  form  of  electrical  current  may  be 
employed  for  this  purpose,  but  galvanism  or  the  induced  current  is  usually 
chosen. 

(1.)  Galvanic  currents  are  usually  obtained  by  the  employment  of  a 
continuous  current  battery  such  as  that  of  Daniell,  by  which  an  elec- 
trical current  which  varies  but  little  in  intensity  is  obtained.  The  bat- 
tery (Fig.  284)  consists  of  a  positive  plate  of  well-amalgamated  zinc  im- 
mersed in  a  porous  cell,  containing  dilute  sulphuric  acid;  and  this  cell 
is  again  contained  within  a  larger  copper  vessel  (forming  the  negative 


408  HANDBOOK    OF    PHYSIOLOGY. 

plate),  containing  besides  a  saturated  solution  of  copper  sulphate.  The 
electrical  current  is  made  continuous  by  the  use  of  the  two  fluids  in  the 
following  manner.  The  action  of  the  dilute  sulphuric  acid  upon  the 
zinc  plate  partly  dissolves  it,  and  liberates  hydrogen,  and  this  gas  passes 
through  the  porous  vessel,  and  decomposes  the  copper  sulphate  into  cop- 
per and  sulphuric  acid.  The  former  is  deposited  upon  the  copper  plate, 
and  the  latter  passes  through  the  porous  vessel  to  renew  the  sulphuric 
acid  which  is  being  used  up.  The  copper  sulphate  solution  is  renewed 
by  spare  crystals  of  the  salt,  which  are  kept  on  a  little  shelf  attached  to 
the  copper  plate,  and  slightly  below  the  level  of  the  solution  in  the 
vessel.  The  current  of  electricity  supplied  by  this  battery  will  continue 
without  variation  for  a  considerable  time.  Other  continuous  current 
batteries,  such  as  Grove's,  may  be  used  in  place  of  Daniell's.  The  way 
in  which  the  apparatus  is  arranged  is  to  attach  wires  to  the  copper  and 
zinc  plates,  and  to  bring  them  to  a  hey,  which  is  a  little  apparatus  for 
connecting  the  wires  of  a  battery.  One  often  employed  is  Du  Bois  Rey- 
mond's   (Fig.  287,   d);  it  consists  of  two  pieces  of  brass  about  an  inch 


Fig.  384.— Diagram  of  a  Daniell's  battery. 

long,  in  each  of  which  are  two  holes  for  wires  and  binding  screws  to  hold 
them  tightly;  these  pieces  of  brass  are  fixed  upon  a  vulcanite  plate,  to 
the  under  surface  of  which  is  a  screw  clamp  by  which  it  can  be  secured 
to  the  table.  The  interval  between  the  pieces  of  brass  can  be  bridged 
over  by  means  of  a  third  thinner  piece  of  similar  metal  fixed  by  a  screw 
to  one  of  the  brass  pieces,  and  capable  of  movement  by  a  handle  at  right 
angles,  so  as  to  touch  the  other  piece  of  brass.  If  the  wires  from  the 
battery  are  brought  to  the  inner  binding  screws,  and  the  bridge  connects 
them,  the  current  passes  across  it  and  back  to  the  batterv.  Wires  are 
connected  with  the  outer  binding  screws,  and  the  other  ends  are  approxi- 
mated for  about  two  inches,  but,  being  covered  except  at  their  points, 
are  insulated,  the  uncovered  points  are  about  an  eighth  of  an  inch  apart. 
These  wires  are  the  electrodes,  and  the  electrical  stimulus  is  applied  to 
the  muscle,  if  they  are  placed  behind  its  nerve,  and  the  connection  be- 
tween the  two  brass  plates  of  the  key  be  broken  by  depressing  the  handle 
of  the  bridge,  and  so  raising  the  connecting  piece  of  metal.  The  key  is 
then  said  to  be  opened. 

(2.)  An  induced  current  is  developed  by  means  of  an  apparatus, 
called  an  induction  coil,  and  the  oneemployed  for  physiological  purposes 
is  mostly  Du  Bois  Eeymond's,  the  one  seen  in  Fig.  285. 


THE    MUSCULAR    SYSTEM. 


400 


Wires  from  a  battery  are  brought  to  the  two  binding  screws  cl  and  d, 
a  key  intervening.  These  binding  screws  are  the  ends  of  a  coil  of  coarse 
covered  wire  c,  called  the  primary  coil.  The  ends  of  a  coil  of  finer 
covered  wire  g,  are  attached  to  two  binding  screws  to  the  left  of  the 
figure,  one  only  of  which  is  visible.  This  is  the  secondary  coil,  and  is 
capable  of  being  moved  nearer  to  c  along  a  grooved  and  graduated  scale. 
To  the  binding  screws  to  the  left  of  g,  the  wires  of  electrodes  used  to 
stimulate  the  muscle  are  attached.  If  the  key  in  the  circuit  of  wires 
from  the  battery  to  the  primary  coil  (primary  circuit)  be  closed,  the  cur- 
rent from  the  battery  passes  through  the  primary  coil,  and  across  the 
key  to  the  battery,  and  continues  to  pass  as  long  as  thekey  continues 
closed.  At  the  moment  of  closure  of  the  key,  at  the  exact  instant  of 
the  completion  of  the  primary  circuit,  an  instantaneous  current  of  elec- 
tricity is  induced  in  the  secondary  coil  g,  if  it  be  sufficiently  near;  and 
the  nearer  it  is  to  c,  the  stronger  is  the  current  induced.  The  current  is 
only  momentary  in  duration,  and  does  not  continue  during  the  whole 
of  the  period  whilst  the  primary  circuit  is  complete.     When,  however, 


Fig.  285.— Du  Bois  Reymond's  induction  coil. 


the  primary  current  is  broken  by  opening  the  key,  a  second,  also  momen- 
tary, current  is  induced  in  g.  The  former  induced  current  is  called  the 
nmking,  and  the  latter  the  breaking  shock;  the  former  is  in  the  opposite 
direction  to,  and  the  latter  in  the  same  as,  the  primary  current. 

The  induction  coil  may  be  used  to  produce  a  rapid  series  of  shocks 
by  means  of  another  and  accessory  part  of  the  apparatus  at  the  right  of 
the  fig.,  called  the  magnetic  interrupter.  If  the  wires  from  a  battery  are 
connected  with  the  two  pillars  by  the  binding  screws,  one  below  c,  and 
the  other,  a,  the  course  of  the  current  is  indicated  in  Fig.  286,  the  direc- 
tion being  indicated  by  the  arrows.  The  current  passes  up  the  pillar  from 
c,  and  along  the  springs  if  the  end  of  d'  is  close  to  the  spring,  the  cur- 
rent passes  to  the  primary  coil  c,  and  to  wires  covering  two  upright  pillars 
of  soft  iron,  from  them  to  the  pillar  a,  and  out  by  the  wires  to  the 
battery;  in  passing  along  the  wire,  b,  the  soft  iron  is  converted  into  a 
magnet,  and  so  attracts  the  hammer,/,  of  the  spring,  breaks  the  connec- 
tion of  the  spring  with  d' ,  and  so  cuts  off  the  current  from  the  primary 
coil,  and  also  from  the  electro-magnet.     As  the  pillars,  b,  are  no  longer 


410 


HANDBOOK    OF    PHYSIOLOGY. 


magnetized  the  spring  is  released,  and  the  current  passes  in  the  first  di- 
rection, and  is  in  like  manner  interrupted.  At  each  make  and  break  of 
the  primary  current,  currents  corresponding  are  induced  in  the  secon- 
dary coil.  These  currents  are  opposite  in  direction,  but  are  not  equal  in 
intensity,  the  break  shock  being  greater.  In  order  that  the  shocks 
should  be  nearly  equal  at  the  make  and  break,  a  wire  (Fig.  286  ef)  con- 
nects e  and  d' ,  and  the  screw  d'  is  raised  out  of  reach  of  the  spring,  and 
d  is  raised  (as  in  Fig.  286),  so  that  part  of  the  current  always  passes 
through  the  primary  coil  and  electro-magnet.  When  the  spring  touches 
d,  the  current  in  b  is  diminished,  but  never  entirely  withdrawn,  and  the 
primary  current  is  altered  in  intensity  at  each  contact  of  the  spring  with 
d,  but  never  entirely  broken. 

Record  of  Muscular  Contraction  under  Stimuli. — The  muscles 
of  the  frog  are  most  convenient  for  the  purpose  of  recording  contractions. 
The  frog  is  pithed,  that  is  to  say,  its  central  nervous  system  is  entirely 
destroyed  by  the  insertion  of  a  stout  needle  into  the  spinal  cord,  and  the 
parts  above  it.  One  of  its  lower  extremities  is  used  in  the  following 
manner.  The  large  trunk  of  the  sciatic  nerve  is  dissected  out  at  the 
back  of  the  thigh,  and  a  pair  of  electrodes  is  inserted  behind  it.     The 


Fig.  286.— Diagram  of  the  course  of  the  current  in  the  magnetic  interrupter  of  Du  Bois  Key- 
mond's  induction  coil.    (Helmholz's  modification.) 

tendo  Achillis  is  divided  from  its  attachment  to  the  os  calcis,  and  a  liga- 
ture is  tightly  tied  round  it.  This  tendon  is  part  of  the  broad  muscle 
of  the  thigh  (gastrocnemius),  which  arises  from  above  the  condyles  of 
the  femur.  The  femur  is  now  fixed  to  a  board  covered  with  cork,  and 
the  ligature  attached  to  the  tendon  is  tied  to  the  upright  of  a  piece  of 
metal  bent  at  right  angles  (Fig.  287,  b),  which  ir  capable  of  movement 
about  the  pivot  at  its  knee,  the  horizontal  portion  carrying  a  writing 
lever  (myograph).  When  the  muscle  contracts,  the  lever  is  raised.  It 
is  necessary  to  attach  a  small  weight  to  the  lever.  In  this  arrangement 
the  muscle  is  in  situ,  and  the  nerve  disturbed  from  its  relations  as  little 
as  possible. 

The  muscle  may,  however,  be  detached  from  the  body  with  the  lower 
end  of  the  femur  from  which  it  arises,  and  the  nerve  going  to  it  may  be 
taken  away  with  it.  The  femur  is  divided  at  about  the  lower  third.  The 
bone  is  held  in  a  firm  clamp,  the  nerve  is  placed  upon  two  electrodes  con- 
nected with  an  induction  apparatus,  and  the  lower  end  of  the  muscle  is 
connected  by  means  of  a  ligature  attached  to  its  tendon  with  a  lever 
which  can  write  on  a  recording  apparatus. 

To  prevent  evaporation  this  so-called  nerve-muscle  preparation  is 


THE    MUSCULAR    SYSTEM. 


411 


placed  under  a  glass  shade,  the  air  in  which  is  kept  moist  by  means  of 
blotting  paper  saturated  with  saline  solution. 

Effects  of  a  Single  Induction  Shock. — With  a  nerve-muscle  pre- 
paration arranged  in  either  of  the  above  ways,  on  closing  or  opening  the 
key  in  the  primary  circuit,  we  obtain  and  can  record  a  contraction,  and 
if  we  use  the  clockwork  apparatus  revolving  rapidly,  a  curve  is  traced 
such  as  is  shown  in  Fig.  288. 

Another  way  of  recording  the  contraction  is  by  the  pendulum  myo- 
graph (Fig.  289).  Here  the  movement  of  the  pendulum  along  a  certain 
arc  is  substituted  for  the  clockwork  movement  of  the  other  apparatus. 
The  pendulum  carries  a  smoked  glass  plate  upon  which  the  writing  lever 
of  a  myograph  is  made  to  mark.     The  opening  or  breaking  shock  is  sent. 


Fig.  287.— Arrangement  of  the  apparatus  necessary  for  recording  muscle  contractions  with  a 
revolving  cylinder  carrying  smoked  paper.  A,  revolving  cylinder;  B,  the  frog  arranged  upon  a 
cork-covered  board  which  is  capable  of  being  raised  or  lowered  on  the  upright,  which  also  can  be 
moved  along  a  solid  triangular  bar  of  metal  attached  to  the  base  of  the  recording  apparatus — the 
tendon  of  the  gastrocnemius  is  attached  to  the  writing  lever,  properly  weighted,  oy  a  ligature. 
The  electrodes  from  the  secondary  coil  pass  to  the  apparatus — being,  for  the  sake  of  conveni- 
ence, first  of  all  brought  to  a  key,  D  (Du  Bois  Reymond'si ;  C.  the  induction  coil;  F,  the  battery  (in 
this  fig.  a  bichromate  one ) ;  E,  the  key  <  Morse's)  in  the  primary  circuit. 

into  the  nerve-muscle  preparation  by  the  pendulum  in  its  swing  opening 
a  key  (Fig.  289,  C.)  in  the  primary  circuit. 

Single  Muscle  Contraction. — The  tracing  obtained  of  a  single 
muscle  contraction  {muscle  curve)  is  seen  in  Fig.  288,  and  may  be  thus 
explained. 

The  upper  line  (m)  represents  the  curve  traced  by  the  end  of  the  lever 
after  stimulation  of  the  muscle  by  a  single  induction-shock:  the  middle 


412  HANDBOOK    OF    PHYSIOLOGY. 

line  (1)  is  that  described  by  trie  marking-lever,  and  indicates  by  a  sudden 
drop  the  exact  instant  at  which  the  induction-shock  was  given.  The 
lower  wavy  line  (t)  is  traced  by  a  vibrating  tuning-fork,  and  serves  to 
measure  precisely  the  intervals  of  time  occupied  in  each  part  of  the  con- 
traction. 

It  will  be  observed  that  after  the  stimulus  has  been  applied,  as  indi- 
cated by  the  vertical  line  s,  there  is  an  interval  before  the  contraction 
commences,  as  indicated  by  the  line  c.  This  interval,  termed  (a)  the 
latent  period,  when  measured  by  the  number  of  vibrations  of  the  tun- 
ing-fork between  the  lines  s  and  c,  is  found  to  be  about  T^-  sec.  The 
latent  period  is  longer  in  some  muscles  than  in  others,  and  differs  also 
according  to  the  condition  of  the  muscle,  being  longer  in  fatigued  mus- 
cles, and  the  kind  of  stimulus  employed.  During  the  latent  period  there 
is  no  apparent  change  in  the  muscle. 


Fig.  288. — Muscle  curve  obtained  by  means  of  the  pendulum  myograph,  s.  indicates  the  exact 
instant  of  the  induction  shock;  c,  commencement;  and  m  x,  the  maximum  elevation  of  lever;  t, 
the  line  of  a  vibrating  tuning-fork.    (M.  Foster.) 

The  second  part  is  the  (b)  stage  of  contraction  proper.  The  lever 
is  raised  by  the  sudden  contraction  of  the  muscle.  The  contraction  ist 
at  first  very  rapid,  but  then  progresses  more  slowly  to  its  maximum,  in- 
dicated by  the  line  m  x,  drawn  through  its  highest  point.  It  occupies  in 
the  figure  T^  sec.  (c)  The  next  stage,  stage  of  elongation.  After 
reaching  its  highest  point,  the  lever  begins  to  descend,  in  consequence 
of  the  elongation  of  the  muscle.  At  first  the  fall  is  rapid,  but  then  be- 
comes more  gradual  until  the  lever  reaches  the  abscissa  or  base  line,  and 
the  muscle  attains  its  precontraction  length,  indicated  in  the  figure  by 
the  line  c'.  This  stage  occupies  Tf„  second.  Very  often  after  the  main 
contraction  the  lever  rises  once  or  twice  to  a  slight  degree,  producing 
curves,  one  of  which  is  seen  in  Fig.  290.  These  contractions,  due  to  the 
elasticity  of  the  muscle,  are  called  most  properly  (d)  Stage  of  elastic 
after-vibration,  or  contraction  remainder. 


THE    MUSCULAR    SYSTEM. 


41* 


The  muscle  curve  obtained  from  the  heart  resembles  that  of  unstriped 
muscles  in  the  long  duration  of  the  effect  of  stimulation;  the  descending 
curve  also  is  very  much  prolonged. 

The  greater  part  of  the  latent  period  is  taken  up  by  changes  in  the 
muscle  itself,  and  the  remainder  occupied  in  the  propagation  of  the 
shock  along  the  nerve. 

Tetanus. — If  we  stimulate  the  nerve-muscle  preparation  with  two 
induction  shocks,  one  immediately  after  the  other,  when  the  point  of 
stimulation  of  the  second  one  corresponds  to  the  maximum  of  the  first, 
a  second  curve  (Fig.  290)  will  occur,  which  will  commence  at  the  highest 
point  of  the  first  and  will  rise  nearly  as  high,  so  that  the  sum  of  the 


Fig.  289.— Simple  form  of  pendulum  myograph  and  accessory  parts.  A,  pivot  upon  which  pen- 
dulum swings;  B,  catch  on  lower  end  of  myograph  opening  the  key,  C,  in  its  swing:  D,  a  spring- 
catch  which  retains  myograph,  as  indicated  by  dotted  lines,  and  on  pressing  down  the  handle  of 
which  the  pendulum  swings  along  the  arc  to  D  on  the  left  of  figure,  and  is  caught  by  its  spring. 


height  of  the  two  curves  almost  exactly  equals  twice  the  height  of  the 
first.  If  a  third  and  a  fourth  shock  be  passed,  a  similar  effect  will  ensue, 
and  curves  one  above  the  other  will  be  traced,  the  third  being  slightly 
less  than  the  second,  and  the  fourth  than  the  third.  If  a  more  numerous 
series  of  shocks  occur,  however,  the  lever  after  a  time  ceases  to  rise  any 
further,  and  the  contraction,  which  has  reached  its  maximum,  is  main- 
tained. The  condition  which  ensues  is  called  Tetanus.  A  tetanus  is 
really  a  summation  of  contractions,  and  unless  the  stimuli  become  very 
rapid  indeed,  the  muscle  will  be  then  in  a  condition  of  vibratory  con- 
traction and  not  of  unvarying  contraction. 


41i  HANDBOOK    OF    PHYSIOLOGY. 

If  the  shocks,  however,  be  repeated  at  very  short  intervals,  being  15 
per  second  for  the  frog's  muscle,  but  varying  in  each  animal,  the  muscle 
contracts  to  its  utmost  suddenly  and  continues  at  its  maximum  contrac- 


Fig.  290.— Tracing  of  a  double  muscle-curve.  To  be  read  from  left  to  right.  While  the  muscle 
'was  engaged  in  the  first  contraction  (whose  complete  course,  had  nothing  intervened,  is  indicated 
by  the  dotted  line),  a  second  induction-shock  was  thrown  in,  at  such  a  time  that  the  second  contrac- 
tion began  just  as  the  first  was  beginning  to  decline.  The  second  curve  is  seen  to  start  from  the 
first,  as  does  the  first  from  the  base  line.    (M.  Foster.) 

tion  for  some  time  and  the  lever  rises  almost  perpendicularly,  and  then 
describes  a  straight  line  (Fig.  292).     If  the   stimuli  are  not   quite  so 


Fig.  291  —Curve  of  tetanus,  obtained  from  the  gastrocnemius  of  a  frog,  where  the  shocks  were 
sent  in  from  an  induction  coil,  about  sixteen  times  a  second,  by  the  interruption  of  the  primary 
current  by  means  of  a  vibrating  spring,  which  dipped  into  a  cup  of  mercury,  and  broke  the  primary 
current  at  each  vibration. 

rapid  the  line  of  maximum  contraction  becomes  somewhat  wavy,  indi- 


Fig.  292.— Curve  of  tetanus,  from  a  series  of  very  rapid  shocks  from  a  magnetic  interrupter. 

eating  a  slight  tendency  of  the  muscle  to  relax  during  the  intervals  be- 
tween the  stimuli  (Fig.  291). 


THE   MUSCULAR    SYSTEM.  4 1 ."» 

Muscular  Work. — We  have  seen  that  work  is  estimated  hy  multi- 
plying the  weight  raised,  by  the  height  through  which  it  has  been  lifted. 
It  has  been  found  that  in  order  to  obtain  the  maximum  of  work,  a  muscle 
must  be  moderately  loaded:  if  the  weight  is  increased  beyond  a  certain 
jioint,  the  muscle  becomes  strained  and  raises  the  weight  through  so 
small  a  distance  that  less  work  is  accomplished.  If  the  load  is  still  fur- 
ther increased  the  muscle  is  completely  overtaxed,  and  cannot  raise  the 


m 

|B1 

■III 

Fig.  293.— Diagram  of  fatigue  muscle-curves.    (Ray  Lankester. ) 

weight.     No  work  is  then  done  at  all.     Practical  illustrations  of  these 
facts  must  be  familiar  to  every  one. 

The  power  of  a  muscle  is  usually  measured  by  the  maximum 
weight  which  it  will  support  without  stretching.  In  man  this  is  readily 
determined  by  weighting  the  body  to  such  an  extent,  that  it  can  no 
longer  be  raised  on  tiptoe:  thus  the  power  of  the  calf-muscles  is  deter- 
mined. The  power  of  muscle  thus  estimated  depends  of  course  upon  its 
cross  section.  The  power  of  a  human  muscle  is  from  two  to  three  times 
as  great  as  a  frog's  muscle  of  the  same  sectional  area. 

Fatigue  of  Muscle. — A  muscle  becomes  rapidly  exhausted  from  re- 
peated stimulation,  and  the  more  rapidly,  the  more  quickly  the  induc- 
tion-shocks succeed  each  other.  This  is  indicated  by  the  diminished 
height  of  the  muscular  contractions. 

It  will  be  seen  in  Fig.  293  that  the  vertical  lines,  which  indicate  the 
extent  of  the  muscular  contraction,  decrease  in  length  from  left  to  right. 
The  line  a  b  drawn  along  the  tops  of  these  lines  is  termed  the  "'  fatigue 
curve."    It  is  usually  a  straight  line. 

In  the  first  diagram  the  effects  of  a  short  rest  are  shown:  there  ifl  a 
pause  of  three  minutes,  and  when  the  muscle  is  again  stimulated,  it 
contracts  up  to  A',  but  the  recovery  is  only  temporary,  and  the  fatigue 


416  HANDBOOK   OF   PHYSIOLOGY. 

curve,  after  a  few  more  contractions,  becomes  continuous  with  that  be- 
fore the  rest. 

In  the  second  diagram  is  represented  the  effect  of  a  stream  of  oxy- 
genated blood.  Here  we  have  a  sudden  restoration  of  energy:  the 
muscle  in  this  case  makes  an  entirely  fresh  start  from  a,  and  the  new 
fatigue  curve  is  parallel  to,  and  never  coincides  with  the  old  one. 

A  fatigued  muscle  has  a  much  longer  latent  period  than  a  fresh  one. 
The  slowness  with  which  muscles  respond  to  the  will  when  fatigued 
must  be  familiar  to  every  one. 

In  a  muscle  which  is  exhausted,  stimulation  only  causes  a  contraction 
producing  a  local  bulging  near  the  point  irritated.  A  similar  effect  may 
be  produced  in  a  fresh  muscle  by  a  sharp  blow,  as  in  striking  the  biceps 
smartly  with  the  end  of  the  hand,  when  a  hard  muscular  swelling  is  in- 
stantly formed. 

Accompaniments  of  Muscular  Contraction. 

(1.)  Heat  is  developed  in  the  contraction  of  muscles.  Becquerel 
and  Breschet  found,  with  the  thermo-multiplier,  about  1°  Fahr.  of  heat 
produced  by  each  forcible  contraction  of  a  man's  biceps;  and  when  the 
actions  were  long  continued,  the  temperature  of  the  muscle  increased 
2°.  This  estimate  is  probably  high,  as  in  the  frog's  muscle  a  consider- 
able contraction  has  been  found  to  produce  an  elevation  of  temperature 
equal  on  an  average  to  less  than  |°  0.  It  is  not  known  whether  this 
development  of  heat  is  due  to  chemical  changes  ensuing  in  the  muscle, 
or  to  the  friction  of  its  fibres  vigorously  acting:  in  either  case  we  may 
refer  to  it  a  part  of  the  heat  developed  in  active  exercise. 

(2. )  Sound  is  said  to  be  produced  when  muscles  contract  forcibly, 
as  mentioned  above.  Wollaston  showed  that  this  sign  might  be  easily 
heard  by  placing  the  tip  of  the  little  finger  in  the  ear,  and  then  making 
some  muscles  contract,  as  those  of  the  ball  of  the  thumb,  whose  sound 
may  be  conducted  to  the  ear  through  the  substance  of  the  hand  and 
finger.  A  low  shaking  or  rumbling  sound  is  heard,  the  height  and  loud- 
ness of  the  note  being  in  direct  proportion  to  the  force  and  quickness  of 
the  muscular  action,  and  to  the  number  of  fibres  that  act  together,  or, 
as  it  were,  in  time. 

(3.)  Changes  in  Shape. — The  mode  of  contraction  in  the  trans- 
versely striated  muscular  tissue  has  been  much  disputed.  The  most 
probable  account  is,  that  the  contraction  is  effected  by  an  approxima- 
tion of  the  constituent  parts  of  the  fibrils,  which,  at  the  instant  of  con- 
traction, without  any  alteration  in  their  general  direction,  become  closer, 
natter,  and  wider;  a  condition  which  is  rendered  evident  by  the  approx- 
imation of  the  transverse  striae  seen  on  the  surface  of  the  fasciculus,  and 
by  its  increased  breadth  and  thickness.  The  appearance  of  the  zigzag 
lines  into  which  it  was  supposed  the  fibres  are  thrown  in  contraction,. 


THE    MUSCULAR    SYSTEM.  41 7 

is  due  to  the  relaxation  of  a  fibre  which  has  been  recently  contracted, 
and  is  not  at  once  stretched  again  by  some  antagonist  fibre,  or  whose 
extremities  are  kept  close  together  by  the  contractions  of  other  fibres. 
The  contraction  is  therefore  a  simple,  and,  according  to  Ed.  Weber,  a 
uniform,  simultaneous,  and  steady  shortening  of  each  fibre  and  its  con- 
tents. What  each  fibril  or  fibre  loses  in  length,  it  gains  in  thickness: 
the  contraction  is  a  change  of  form  not  of  size;  it  is,  therefore,  not  at- 
tended with  any  diminution  in  bulk,  from  condensation  of  the  tissue. 
This  has  been  proved  for  entire  muscles,  by  making  a  mass  of  muscle, 
or  many  fibres  together,  contract  in  a  vessel  full  of  water,  with  which  a 
fine,  perpendicular,  graduated  tube  communicates.  Any  diminution  of 
the  bulk  of  the  contracting  muscle  would  be  attended  by  a  fall  of  fluid 
in  the  tube;  but  when  the  experiment  is  carefully  performed,  the  level 
of  the  water  in  the  tube  remains  the  same,  whether  the  muscle  be  con- 
tracted or  not. 

In  thus  shortening,  muscles  appeal'  to  sioell  up,  becoming  rounder, 
more  prominent,  harder,  and  apparently  tougher.     But  this  hardness  of 


Fig.  294.— The  microscopic  appearances  during  a  muscular  contraction  in  the  individual  fibrillar 
after  Engelmann.  1.  A  passive  muscle  fibre;  c  to  d  =  doubly  refractive  discs,  with  median  disc  a  b 
in  it;  h  and  g  are  lateral  discs;  f  and  e  are  secondary  discs,  only  slightly  doubly  refractive;  fig. 
on  right  same  fibre  in  polarized  light;  bright  part  is  doubly  refracted,  black  ends  not  so.  2.  Transi- 
tion stage ;  and  3.  Stage  of  entire  contraction ;  in  each  ease  the  right-hand  figure  represents  the 
effect  of  polarized  light.    (Landois  after  Engelmann.) 

muscle  in  the  state  of  contraction,  is  not  due  to  increased  firmness  or 
condensation  of  the  muscular  tissue,  but  to  the  increased  tension  to 
which  the  fibres,  as  well  as  their  tendons  and  other  tissues,  are  subjected 
from  the  resistance  ordinarily  opposed  to  their  contraction.  When  no 
resistance  is  offered,  as  when  a  muscle  is  cut  off  from  its  tendon,  not 
only  is  no  hardness  perceived  during  contraction,  but  the  muscular  tis- 
sue is  even  softer,  more  extensile,  and  less  elastic  than  in  its  ordinarv 
uncontracted  state.  During  contraction  in  each  fibre  it  is  said  that  the 
anisotropous  or  doubly  refractive  elements  become  less  refractive  and  the 
singly  refractive  more  so  (Fig.  294). 

(4.)  Chemical  changes.— (a)  The  reaction  of  the  muscle  which  is 
normally  alkaline  or  neutral  becomes  decidedly  acid,  from  the  develop- 
ment of  sarcolactic  acid,  (b)  The  muscle  gives  out  carbonic  acid  gas 
and  takes  up  oxygen,  the  amount  of  the  COa  given  out  not  appearing  to 

be  entirely  dependent  upon  the  0  taken  in,   and  so  doubtless  in  part 

27 


418 


HANDBOOK    OF    PHYSIOLOGY. 


arising  from  some  other  source.  (6')  Certain  imperfectly  understood 
chemical  changes  occur,  in  all  probability  connected  with  (a)  and  (&). 
Glycogen  is  diminished,  and  glucose,  or  muscle  sugar  (inosite)  appears; 
the  extractives  are  increased. 

(5.)  Electrical  changes. — When  a  muscle  contracts  the  natural 
muscle  current  or  currents  of  rest  undergo  a  distinct  diminution,  which 
is  due  to  the  appearance  in  the  actively  contracting  muscle  of  currents  in 
an  opposite  direction  to  those  existing  in  the  muscle  at  rest.  This  causes 
a  temporary  deflection  of  the  needle  of  a  galvanometer  in  a  direction  op- 
posite to  the  original  current,  and  is  called  by  some  the  negative  varia- 
tion of  the  muscle  current,  and  by  others  a  current  of  action. 

Conditions  of  Contraction.— (a)  The  irritability  of  muscle,  as  in- 
dicated by  length  of  latent  period,  velocity  and  extent  of  contraction, 
is  greatest  at  a  certain  mean  temperature;  (b)  after  a  number  of  contrac- 
tions a  muscle  gradually  becomes  exhausted;  (c)  the  activity  of  muscles 
after  a  time  disappears  altogether  when  they  are  removed  from  the  body 
or  the  arteries  are  tied;  (d)  oxygen  is  used  up  in  muscular  contraction, 


Fig.  295.— Muscle-curves  from  the  gastrocnemius  of  a  frog,  illustrating  effects  of  alterations  in 
temperature. 

but  a  muscle  will  act  for  a  time  in  vacuo  or  in  a  gas  which  contains  no 
oxygen:  in  this  case  it  is  of  course  using  up  the  oxygen  already  in  store; 
(e)  the  contraction  is  greater  if  the  stimulus  is  applied  to  the  nerve,  than 
if  it  be  applied  to  the  muscle  directly. 

Response  to  Stimuli. — The  two  kinds  of  fibres,  the  striped  and 
the  unstriped,  have  characteristic  differences  in  the  mode  in  which  they 
act  on  the  application  of  the  same  stimulus;  differences  which  may  be 
ascribed  in  great  part  to  the  respective  differences  of  structure,  but  to 
some  degree,  possibly,  to  their  respective  modes  of  connection  with  the 
nervous  system.  When  irritation  is  applied  directly  to  a  muscle  with 
striated  fibres,  or  to  the  motor  nerve  supplying  it,  contraction  of  the 
part  irritated,  and  of  that  only,  ensues;  and  this  contraction  is  instanta- 
neous, and  ceases  on  the  instant  of  withdrawing  the  irritation.  But 
when  any  part  with  unstriped  muscular  fibres,  e.  g.,  the  intestines  or 
bladder,  is  irritated,  the  subsequent  contraction  ensues  more  slowly,  ex- 
tends beyond  the  part  irritated,  and,  with  alternating  relaxation,  con- 
tinues for  some  time  after  the  withdrawal  of  the  irritation.  The  differ- 
ence in  the  modes  of  contraction  of  the  two  kinds  of  muscular  fibres 
may  be  particularly  illustrated  by  the  effects  of  the  repeated  stimuli 


THE    MUSOULAB    SYSTEM.  41'.' 

with  the  magnetic  interrupter.  The  rapidly  succeeding  shocks  given  by 
this  means  to  the  nerves  of  muscles  excite  in  all  the  transversely-striated 
muscles,  except  in  the  case  of  the  heart,  a  fixed  state  of  tetanic  contrac- 
tion as  previously  described,  which  lasts  as  long  as  the  stimulus  is  con- 
tinued, and  on  its  withdrawal  instantly  ceases;  but  in  the  muscles  with 
unstriped  fibres  they  excite  a  slow  vermicular  movement;  which  is  com- 
paratively slight  and  alternates  with  rest.  It  continues  for  a  time  after 
the  stimulus  is  withdrawn. 

In  their  mode  of  responding  to  these  stimuli,  all  the  skeletal  muscles, 
or  those  with  transverse  strise,  are  alike;  but  among  those  with  unstriped 
fibres  there  are  many  differences — a  fact  which  tends  to  confirm  the 
opinion  that  their  peculiarity  depends  as  well  on  their  connection  with 
nerves  and  ganglia  as  on  their  own  properties.  The  ureters  and  gall- 
bladder are  the  parts  least  excited  by  stimuli;  they  do  not  act  at  all  till 
the  stimulus  has  been  long  applied,  and  then  contract  feebl}T,  and  to  a 
small  extent.  The  contractions  of  the  cfecum  and  stomach  are  quicker 
and  wider-spread:  still  quicker  those  of  the  iris,  and  of  the  urinary  blad- 
der if  it  be  not  too  full.  The  actions  of  the  small  and  large  intestines, 
of  the  vas  deferens,  and  pregnant  uterus,  are  yet  more  vivid,  more  regu- 
lar, and  more  sustained;  and  they  require  no  more  stimulus  than  that  of 
the  air  to  excite  them.  The  heart,  on  account,  doubtless,  of  its  striated 
muscle,  is  the  quickest  and  most  vigorous  of  all  the  muscles  of  organic 
life  in  contracting  upon  irritation,  and  appears  in  this,  as  in  nearly  all 
others  respects,  to  be  the  connecting  member  of  the  two  classes  of 
muscles. 

All  the  muscles  retain  their  property  of  contracting  under  the  influ- 
ence of  stimuli  applied  to  them  or  to  their  nerves  for  some  time  after 
death,  the  period  being  longer  in  cold-blooded  than  in  warm-blooded 
Vertebrata,  and  shorter  in  Birds  than  in  Mammalia.  It  would  seem  as 
if  the  more  active  the  respiratory  process  in  the  living  animal,  the 
shorter  is  the  time  of  duration  of  the  irritability  in  the  muscles  after 
death:  and  this  is  confirmed  by  the  comparison  of  different  species  in 
the  same  order  of  Vertebrata.  But  the  period  during  which  this  irri- 
tability lasts,  is  not  the  same  in  all  persons,  nor  in  all  the  muscles  of 
the  same  persons.  In  a  man  it  ceases,  according  to  Nysten,  in  the  fol- 
lowing order: — first  in  the  left  ventricle,  then  in  the  intestines  and 
stomach,  the  urinary  bladder,  right  ventricle,  oesophagus,  iris;  then  in 
the  voluntary  muscles  of  the  trunk,  lower  and  upper  extremities;  lastly, 
in  the  right  and  left  auricle  of  the  heart. 

C.  Rigor  Mortis. 

After  the  musclesof  the  dead  body  have  lost  their  irritability  or  capa- 
bility of  being  excited  to  contraction  by  the  application  of  a  stimulus, 
they  spontaneously  pass  into  a  state  of  contraction,  apparently  identical 
with  that  which  ensues  during  life.  It  affects  all  the  muscles  of  the 
body;  and,  where  external  circumstances  do  not  prevent  it,  commonly 
fixes  the  limbs  in  that  which  is  their  natural  posture  of  equilibrium  or 
rest.     Hence,  and  from  the  simultaneous  contraction  of  all  the  muscles 


420  HANDBOOK    OF  PHYSIOLOGY. 

of  the  trunk,  is  produced  a  general  stiffening  of  the  body,  constituing 
the  rigor  mortis  or  post-mortem  rigidity. 

When  this  condition  has  set  in,  the  muscle  (a)  becomes  acid  in  reaction, 
(due  to  development  of  sarco-lactic  acid),  (b)  gives  off  carbonic  acid  in 
great  excess,  (c)  Its  volume  is  slightly  diminished;  (d)  the  muscular  fibres 
become  shortened  and  opaque,  and  their  substance  sets  firm.  It  comes 
on  much  more  rapidly  after  muscular  activity,  and.  is  hastened  by 
warmth.  It  may  be  brought  on,  in  muscles  exposed  for  experiment,  by 
the  action  of  distilled  water  and  many  acids,  also  by  freezing  and  thaw- 
ing again. 

Cause. — The  immediate  cause  of  rigor  seems  to  be  a  chemical  one, 
namely,  the  coagulation  of  the  muscle  plasma.  We  may  distinguish 
three  main  stages — (1.)  Gradual  coagulation.  (2.)  Contraction  of  coagu- 
lated muscle-clot  (myosin),  and  squeezing  out  of  muscle-serum.  (3.) 
Putrefaction.  After  the  first  stage,  restoration  is  possible  through  the 
circulation  of  arterial  blood  through  the  muscles,  and  even  when  the 
second  stage  has  set  in,  vitality  may  be  restored  by  dissolving  the  coagu- 
lum  of  the  muscle  in  salt  solution,  and  passing  arterial  blood  through  its 
vessels.     In  the  third  stage  recovery  is  impossible. 

Order  of  Occurrence. — The  muscles  are  not  affected  simultaneously 
by  rigor  mortis.  It  affects  the  neck  and  lower  jaw  first;  next,  the  upper 
extremities,  extending  from  above  downwards;  and  lastly,  reaches  the 
lower  limbs;  in  some  rare  instances  only,  it  affects  the  lower  extremities 
before,  or  simultaneously  with,  the  upper  extremities.  It  usually  ceases 
in  the  order  in  which  it  began:  first  at  the  head,  then  in  the  upper  ex- 
tremities, and  lastly,  in  the  lower  extremities.  It  never  commences 
earlier  than  ten  minutes,  and  never  later  than  seven  hours,  after  death; 
and  its  duration  is  greater  in  proportion  to  the  lateness  of  its  accession. 
Heat  is  developed  during  the  passage  of  a  muscular  fibre  into  the  condi- 
tion of  rigor  mortis. 

Since  rigidity  does  not  ensue  until  muscles  have  lost  the  capacity  of 
being  excited  by  external  stimuli,  it  follows  that  all  circumstances  which 
cause  a  speedy  exhaustion  of  muscular  irritability,  induce  an  early  occur- 
rence of  the  rigidity,  while  conditions  by  which  the  disappearance  of  the 
irritability  is  delayed,  are  succeeded  by  a  tardy  onset  of  this  rigidity. 
Hence  its  speedy  occurrence,  and  equally  speedy  departure  in  the  bodies 
of  persons  exhausted  by  chronic  diseases;  and  its  tardy  onset  and.  long 
continuance  after  sudden  death  from  acute  diseases.  In  some  cases  of 
sudden  death  from  lightning,  violent  injuries,  or  paroxysms  of  passion, 
rigor  mortis  has  been  said  not  to  occur  at  all;  but  this  is  not  always  the 
case.  It  may,  indeed,  be  doubted  whether  there  is  really  a  complete 
absence  of  the  post-mortem  rigidity  in  any  such  cases;  for  the  experi- 
ments   of    Brown-Sequard  make    it    probable  that    the    rigidity   may 


THE    MUSCULAR    SYSTEM.  421 

supervene  immediately  after  death,  and  then  pass  away  with  such  rapidity 
as  to  be  scarcely  observable. 

Experiments. — Brown-Sequard  took  five  rabbits,  and  killed  them  by 
removing  their  hearts.  In  the  first,  rigidity  came  on  in  10  hours,  and 
lasted  192  hours;  in  the  second,  which  was  feebly  electrified,  it  com- 
menced in  7  hours,  and  lasted  144;  in  the  third,  which  was  more  strongly 
•electrified,  it  came  on  in  two,  and  lasted  72  hours;  in  the  fourth,  which 
was  still  more  strongly  electrified,  it  came  on  in  one  hour,  and  lasted  20; 
while,  in  the  last  rabbit,  which  was  submitted  to  a  powerful  electro-gal- 
vanic current,  the  rigidity  ensued  in  seven  minutes  after  death,  and 
passed  away  in  25  minutes.  From  this  it  appears  that  the  more  powerful 
the  electric  current,  the  sooner  does  the  rigidity  ensue,  and  the  shorter 
is  its  duration;  and  as  the  lightning  shock  is  so  much  more  powerful 
than  any  ordinary  electric  discharge,  the  rigidity  may  ensue  so  early 
after  death,  and  pass  away  so  rapidly  as  to  escape  detection.  The  in- 
fluence exercised  upon  the  onset  and  duration  of  post-mortem  rigidity 
by  causes  which  exhaust  the  irritability  of  the  muscles,  was  well  illus- 
trated in  further  experiments  by  the  same  physiologist,  in  which  he  found 
that  the  rigor  mortis  ensued  far  more  rapidly,  and  lasted  for  a  shorter 
period  in  those  muscles  which  had  been  powerfully  electrified  just  before 
death  thau  those  which  had  not  been  thus  acted  upon. 

The  occurrence  of  rigor  mortis  is  not  prevented  by  the  previous  exist- 
ence of  paralysis  in  a  part,  provided  the  paralysis  has  not  been  attended 
with  very  imperfect  nutrition  of  the  muscular  tissue. 

The  rigidity  affects  the  involuntary  as  well  the  voluntary  muscles, 
whether  they  be  constructed  of  striped  or  unstriped  fibres.  The  rigidity 
of  involuntary  muscles  with  striped  fibres  is  shown  in  the  contraction  of 
the  heart  after  death.  The  contraction  of  the  muscles  with  unstriped 
fibres  is  shown  by  an  experiment  of  Valentin,  who  found  that  if  a  gradu- 
ated tube  connected  with  a  portion  of  intestine  taken  from  a  recently- 
killed  animal,  be  filled  with  water,  and  tied  at  the  opposite  end,  the 
water  will  in  a  few  hours  rise  to  a  considerable  height  in  the  tube,  owing 
to  the  contraction  of  the  intestinal  walls.  It  is  still  better  shown  in  the 
arteries,  of  which  all  that  have  muscular  coats  contract  after  death,  and 
thus  present  the  roundness  and  cord-like  feel  of  the  arteries  of  a  limb 
lately  removed,  or  those  of  a  body  recently  dead.  Subsequently  they 
relax,  as  do  all  the  other  muscles,  and  feel  lax  and  flabby,  and  lie  as  if 
flattened,  and  with  their  walls  nearly  in  contact. 

Actions  of  the  Voluntary  Muscles. 

The  greater  part  of  the  voluntary  musclss  of  the  body  act  as  sources 
of  power  for  removing  levers — the  latter  consisting  of  the  various  bones  to 
which  the  muscles  are  attached. 

Examples  of  the  three  orders  of  levers  in  the  Human  Body. — 

All  levers  have  been  divided  into  three  kinds,  according  to  the  relative 


422 


HANDBOOK    OF    PHYSIOLOGY. 


position  of  the  power,  the  weight  to  be  removed,  and  the  axis  of  motion 
ox  fulcrum.  In  a  lever  of  the  first  kind  the  power  is  at  one  extremity  of 
the  lever,  the  weight  at  the  other,  and  the  fulcrum  between  the  two. 
If  the  initial  letters  only  of  the  power,  weight,  and  fulcrum  be  used,  the 
arrangement  will  stand  thus: — P.F.W.  A  poker  as  ordinarily  used,  or 
the  bar  in  Fig.  296,  may  be  cited  as  an  example  of  this  variety  of  lever; 
while,  as  an  instance  in  which  the  bones  of  the  human  skeleton  are  used 
as  a  lever  of  the  same  kind,  may  be  mentioned  the  act  of  raising  the  body 


Fig.  296. 


from  the  stooping  posture  by  means  of  the  hamstring  muscles  attached 
to  the  tuberosity  of  the  ischium  (Fig.  296). 

In  a  lever  of  the  second  kind,  the  arrangement  is  thus: — P.W.F. ; 
and  this  leverage  is  employed  in  the  act  of  raising  the  handles  of  a  wheel- 
barrow, or  in  stretching  an  elastic  band,  as  in  Fig.  297.     In  the  human 


P      .  TV 


w-3Ls 


EuasticIiBand 


Fig.  297. 


body  the  act  of  opening  the  mouth  by  depressing  the  lower  jaw  is  an  ex- 
ample of  the  same  kind — the  tension  of  the  muscles  which  close  the  jaw 
representing  the  weight  (Fig.  297).  t 

In  a  lever  of  the  third  kind  the  arrangement  is — F.P.W.,  and  the  act 
of  raising  a  pole,  as  in  Fig.  298,  is  an  example.  In  the  human  body 
there  are  numerous  examples  of  the  employment  of  this  kind  of  leverage. 
The  act  of  bending  the  fore-arm  may  be  mentioned  as  an  instance  (Fig- 
298).     The  act  of  biting  is  another  example. 


THE    MUSCULAR    SYSTEM. 


423 


At  the  ankle  we  have  examples  of  all  three  kinds  of  lever.  1st  kind 
— Extending  the  foot.  3d  kind — Flexing  the  foot.  In  both  these  cases 
the  foot  represents  the  weight:  the  ankle  joint  the  fnlcrnm,  the  power 
being  the  calf  muscles  in  the  first  case  and  the  tibialis  anticus  in  the 
second  case.  ■  2d  kind— When  the  body  is  raised  on  tip-toe.  Here  the 
ground-  is  the  fulcrum,  the  weight  of  the  body  acting  at  the  ankle  joint 
the  weight,  and  the  calf  muscles  the  power. 

In  the  human  body,  levers  are  most  frequently  used  at  a  disadvantage 
as  regards  power,  the  latter  being  sacrificed  for  the  sake  of  a  greater 
range  of  motion.  Thus  in  the  diagrams  of  the  first  and  third  kinds  it  is 
evident  that  the  power  is  so  close  to  the  fulcrum,  that  great  force  must 
be  exercised  in  order  to  produce  motion.  It  is  also  evident,  however, 
from  the  same  diagrams,  that  by  the  closeness  of  the  power  to  the  ful- 
crum a  great  range  of  movement  can  be  obtained  by  means  of  a  com- 
paratively slight  shortening  of  the  muscular  fibres. 

The  greater  number  of  the  more  important  muscular  actions  of  the 
human  body — those,  namely,  which  are  arranged  harmoniously  so  as  to 


Fig.  298. 


subserve  some  definite  purpose  or  other  in  the  animal  economy — are  de- 
scribed in  various  parts  of  this  work,  in  the  sections  which  treat  of  the 
physiology  of  the  processes  by  which  these  muscular  actions  are  resisted 
or  carried  out.  There  are,  however,  one  or  two  very  important  and 
somewhat  complicated  muscular  acts  which  may  be  described  in  this 
place. 

Walking. — In  the  act  of  walking,  almost  every  voluntary  muscle  in 
the  body  is  brought  into  play,  either  directly  for  purposes  of  progres- 
sion, or  indirectly  for  the  proper  balancing  of  the  head  and  trunk.  The 
muscles  of  the  arms  are  least  concerned;  but  even  these  are  for  the  most 
part  instinctively  in  action  also  to  some  extent. 

Among  the  chief  muscles  engaged  directly  in  the  act  of  walking  are 
those  of  the  calf,  which,  by  pulling  up  the  heel,  pull  up  also  the  astrag- 
alus, and  with  it,  of  course,  the  whole  body,  the  weight  of  which  is 
transmitted  through  the  tibia  to  this  bone  (Fig.  298).  When  starting 
to  walk,  say  with  the  left  leg,  this  raising  of  the  body  is  not  left  entirely 
to  the  muscles  of  the  left  calf,  but  the  trunk  is  thrown  forward  in  such 
a  way,  that   it  would  fall  prostrate  were  it  not   that  the  right  foot  is 


424 


HANDBOOK    OF    PHYSIOLOGY. 


brought  forward  and  planted  on  the  ground  to  support  it.  Thus  the 
muscles  of  the  left  calf  are  assisted  in  their  action  by  those  muscles  on 
the  front  of  the  trunk  and  legs  which,  by  their  contraction,  pull  the 
body  forwards;  and,  of  course,  if  the  trunk  form  a  slanting  line,  with 
the  inclination  forwards,  it  is  plain  that  when  the  heel  is 'raised  by  the 
calf-muscles,  the  whole  body  will  be  raised,  and  pushed  obliquely  for- 
wards and  upwards.  The  successive  acts  in  taking  the  first  step  in  walk- 
ing are  represented  in  Fig.  299,  1,  2,  3. 

Now  it  is  evident  that  by  the  time  the  body  has  assumed  the  position 
No.  3,  it  is  time  that  the  right  leg  should  be  brought  forward  to  support 
it  and  prevent  it  from  falling  prostrate.  This  advance  of  the  other  leg 
(in  this  case  the  right)  is  effected  partly  by  its  mechanically  swinging 
forwards,  pendulum-wise,  and  partly  by  muscular  action;  the  muscles 
used  being — 1st,  those  on  the  front  of  the  thigh,  which  bend  the  thigh 
forwards  on  the  pelvis,  especially  the  rectus  femoris,  with  the  psoas  and 
the  iliacus;  %dly,  the  hamstring  muscles,  which  slightly  bend  the  leg 
on  the  thigh;  and  Mly,  the  muscles  on  the  front  of  the  leg,  which 
raise  the  front  of  the  foot  and  toes,  and  so  prevent  the  latter  in  swinging 
forwards  from  hitching  in  the  ground. 

The  second  part  of  the  act  of  walking,  which  has  been  just  described 
is  shown  in  the  diagram  (4,  Fig.  299). 


When  the  right  foot  has  reached  the  ground  the  action  of  the  left 
leg  has  not  ceased.  The  calf-muscles  of  the  latter  continue  to  act,  and 
by  pulling  up  the  heel,  throw  the  body  still  more  forwards  over  the  right 
leg,  now  bearing  nearly  the  whole  weight,  until  it  is  time  that  in  its  turn 
the  left  leg  should  swing  forwards,  and  the  left  foot  be  planted  on  the 
ground  to  prevent  the  body  from  falling  prostrate.  As  at  first,  while 
the  calf  muscles  of  one  leg  and  foot  are  preparing,  so  to  speak,  to  push 
the  body  forward  and  upward  from  behind  by  raising  the  heel,  the  mus- 
cles on  the  front  of  the  trunk  and  of  the  same  leg  (and  of  the  other  leg, 
except  when  it  is  swinging  forwards)  are  helping  the  act  by  pulling  the 
legs  and  trunk,  so  as  to  make  them  incline  forward,  the  rotation  in  the 
inclining  forwards  being  effected  mainly  at  the  ankle  joint.  Two  main 
kinds  of  leverage  are,  therefore,  employed  in  the  act  of  walking,  and  if 
this  idea  be  firmly  grasped,  the  details  will  be  understood  with  compara- 
tive ease.  On  kind  of  leverage  employed  in  walking  is  essentially  the 
same  with  that  employed  in  pulling  forward  the  pole,  as  in  Fig.  298. 
And  the  other,  less  exactly,  is  that  employed  in  raising  the  handles  of  a 
wheelbarrow.  Now,  supposing  the  lower  end  of  the  pole  to  be  placed 
in  the  barrow,  we  should  have  a  very  rough  and  inelegant,  but  not  alto- 
gether bad  lepresentation  of  the  two  main  levers  employed  in  the  act  of 
walking.     The  body  is  pulled  forward  by  the  muscles  in  front,  much  in 


THE   MUSCULAR    SYSTEM. 


425 


the  same  way  that  the  pole  might  be  by  the  force  applied  at  p.  (Fig. 
298),  while  the  raising  of  the  heel  and  pushing  forwards  of  the  trunk  by 
the  calf-muscles  is  roughly  represented  on  raising  the  handles  of  the  bar- 
row. The  manner  in  which  these  actions  are  performed  alternately  by 
each  leg,  so  that  one  after  the  other  is  swung  forwards  to  support  the 
trunk,  which  is  at  the  same  timepushed  and  pulled  forwards  by  the  mus- 
cles of  the  other,  may  be  gathered  from  the  previous  description. 

There  is  one  more  thing  to  be  noticed  especially  in  the  act  of  walk- 
ing. Inasmuch  as  the  body  is  being  constantly  supported  and  balanced 
on  each  leg  alternately,  and  therefore  on  only  one  at  the  same  moment, 
it  is  evident  that  there  must  be  some  provision  made  for  throwing  the 
centre  of  gravity  over  the  line  of  support  formed  by  the  bones  of  each 
leg,  as,  in  its  turn,  it  supports  the  weight  of  the  body.  This  may  be 
done  in  various  way,  and  the  manner  in  which  it  is  effected  is  one  ele- 


If  Inn 

\/ 

if  ill 

Vv 

• 

Fig.  300. 


ment  in  the  differences  which  exist  in  the  walking  of  different  people. 
Thus  it  may  be  done  by  an  instinctive  slight  rotation  of  the  pelvis  on  the 
head  of  each  femur  in  turn,  in  such  a  manner  that  the  centre  of  grav- 
ity of  the  body  shall  fall  over  the  foot  of  this  side.  Thus  when  the 
body  is  pushed  onwards  and  upwards  by  the  raising,  say,  of  the  right 
heel,  as  in  Fig.  299,  3,  the  pelvis  is  instinctively  by  various  muscles, 
made  to  rotate  on  the  head  of  the  left  femur  at  the  acetabulum,  to  the 
left  side,  so  that  the  weight  may  fall  over  the  line  of  support  formed  by 
the  left  leg  at  the  time  that  the  right  leg  is  swinging  forwards,  and  leav- 
ing all  the  work  of  support  to  fall  on  its  fellow.  Such  a  "rocking" 
movement  of  the  trunk  and  pelvis,  however,  is  accompanied  by  a  move- 
ment of  the  whole  trunk  and  leg  over  the  foot  wrhich  is  being  planted  on 
the  ground  (Fig.  300);  the  action  being  accompanied  with  a  compensa- 
tory outward  movement  at  the  hip,  more  easily  appreciated  by  looking 
at  the  figure  (in  which  this  movement  is  shown  exaggerated)  than  de- 
scribed. 


426  HANDBOOK   OF    PHYSIOLOGY. 

Thus  the  body  in  walking  is  continually  rising  and  swaying  alter- 
nately from  one  side  to  the  other,  as  its  centre  of  gravity  has  to  be 
brought  alternately  over  one  or  other  leg;  and  the  curvatures  of  the  spine 
are  altered  in  correspondence  with  the  varying  position  of  the  weight 
which  it  has  to  support.  The  extent  to  which  the  body  is  raised  or 
swayed  differs  much  in  different  people. 

In  walking,  one  foot  or  the  other  is  always  on  the  ground.  The  act 
of  leaping  or  jumping,  consists  in  so  sudden  a  raising  of  the  heels  by 
the  sharp  and  strong  contraction  of  the  calf-muscles,  that  the  body  is 
jerked  off  the  ground.  At  the  same  time  the  effect  is  much  increased 
by  first  bending  the  thighs  on  the  pelvis,  and  the  legs  on  the  thighs,  and 
then  suddenly  straightening  out  the  angles  thus  formed.  The  share 
which  this  action  has  in  producing  the  effect  may  be  easily  known  by 
attempting  to  leap  in  the  upright  posture,  with  the  legs  quite  straight. 

Running  is  performed  by  a  series  of  rapid  low  jumps  with  each  leg 
alternately;  so  that,  during  each  complete  muscular  act  concerned,  there 
is  a  moment  when  both  feet  are  off  the  ground. 

In  all  these  cases,  however,  the  description  of  the  manner  in  which 
any  given  effect  is  produced,  can  give  but  a  very  imperfect  idea  of  the 
infinite  number  of  combined  and  harmoniously  arranged  muscular  con- 
tractions which  are  necessary  for  even  the  simplest  acts  of  locomotion. 

Action  of  the  Involuntary  Muscles.— The  involuntary  muscles 
are  for  the  most  part  not  attached  to  bones  arranged  to  act  as  levers,  but 
enter  into  the  formation  of  such  hollow  parts  as  require  a  diminution  of 
their  calibre  by  muscular  action,  under  particular  circumstances.  Ex- 
amples of  this  action  are  to  be  found  in  the  intestines,  urinary  bladder, 
heart  and  blood-vessels,  gall-bladder,  gland-ducts,  etc. 

The  difference  in  the  manner  of  contraction  of  the  striated  and  non- 
striated  fibres  has  been  already  referred  to  (p.  418);  and  the  peculiar 
vermicular  or  peristaltic  action  of  the  latter  fibres  has  been  described  at 
p.  419. 

Source  of  Muscular  Action. — It  was  formerly  supposed  that  each 
act  of  contraction  on  the  part  of  a  muscle  was  accompanied  by  a  correla- 
tive waste  or  destruction  of  its  own  substance;  and  that  the  quantity  of 
the  nitrogenous  excreta,  especially  of  urea,  presumably  the  expression  of 
this  waste,  was  in  exact  proportion  to  the  amount  of  muscular  work  per- 
formed. It  has  been  found,  however,  both  that  the  theory  itself  is  erro- 
neous, and  that  the  supposed  facts  on  which  it  was  founded  do  not  exist. 

It  is  true  that  in  the  action  of  muscles,  as  of  all  other  parts,  there  is 
a  certain  destruction  of  tissue  or,  in  other  words,  a  certain  '  wear  and 
tear*  which  may  be  represented  by  a  slight  increase  in  the  quantity  of 
urea  excreted;  but  it  is  not  the  correlative  expression  or  only  source  of 
the  power  manifested.  The  increase  in  the  amount  of  urea  which  is 
excreted  after  muscular  exertion  is  by  no  means  so  great  as  was  formerly 
supposed;  indeed,  it  is  very  slight.  And  as  there  is  no  reason  to  believe 
that  the  waste  of  muscle-substance  can  be  expressed,  with  unimportant  ex- 
ceptions, in  any  other  way  than  by  an  increased  excretion  of  urea,  it  is 


THE    MUSCULAR    SYSTEM.  427 

evident  that  we  must  look  elsewhere  than  in  destruction  of  muscle,  for 
the  source  of  muscular  action.  For,  it  need  scarcely  be  said,  all  force 
manifested  in  the  living  body  must  be  the  correlative  expression  of  force 
previously  latent  in  the  food  eaten  or  the  tissue  formed;  and  evidences 
of  force  expended  in  the  body  must  be  found  in  the  excreta.  If,  therefore 
the  nitrogenous  excreta,  represented  chiefly  by  urea,  are  not  in  sufficient 
quantity  to  account  for  the  work  done,  Ave  must  look  to  the  non-nitro- 
genous excreta,  as  carbonic  acid  and  water,  which,  presumably,  cannot 
be  the  expression  of  wasted  muscle-substance. 

The  quantity  of  these  non-nitrogenous  excreta  is  undoubtedly 
increased  by  active  muscular  efforts,  and  to  a  considerable  extent;  and 
whatever  may  be  the  source  of  the  water,  the  carbonic  acid,  at  least,  is 
the  result  of  chemical  action  in  the  system,  and  especially  of  the  com- 
bustion of  non-nitrogenous  food,  although,  doubtless,  of  nitrogenous 
food  also.  We  are,  therefore,  driven  to  the  conclusion — that  the  sub- 
stance of  muscles  is  not  wasted  in  proportion  to  the  work  they  perform: 
and  that  the  non-nitrogenous  as  well  as  the  nitrogenous  foods  may,  in 
their  combustion,  afford  the  requisite  conditions  for  muscular  action. 
The  urgent  necessity  for  nitrogenous  food,  especially  after  exercise,  is 
probably  due  more  to  the  need  of  nutrition  by  the  exhausted  muscles  and 
other  tissues  for  which,  of  course,  nitrogen  is  essential,  than  to  such  food 
being  superior  to  non-nitrogenous  substances  as  a  source  of  muscular 
power. 

Electrical  Currents  in"  Nerves. 

The  electrical  condition  of  Nerves  is  so  closely  connected  with  the 
phenomena  of  muscular  contraction,  that  it  will  be  convenient  to  con- 
sider it  in  the  present  chapter. 

If  a  piece  of  nerve  be  removed  from  the  body  and  subjected  to  exam- 
ination in  a  way  similar  to  that  adopted  in  the  case  of  muscle  which  has 
been  described  (p.  404),  electrical  currents  are  found  to  exist  which  cor- 
respond exactly  to  the  natural  muscle  currents,  and  which  are  called 
natural  nerve  currents  or  currents  of  rest,  according  as  one  or  other 
theory  of  their  existence  be  adopted,  as  in  the  case  with  muscle.  One 
point  (equator)  on  the  surface  being  positive  to  all  other  points  nearer 
to  the  cut  ends,  and  the  greatest  deflection  of  the  needle  of  the  galvano- 
meter taking  place  when  one  electrode  is  applied  to  the  equator  and  the 
other  to  the  centre  of  either  cut  end.  As  in  the  case  of  muscle,  these 
nerve-currents  undergo  a  negative  variation  when  the  nerve  is  stimulated, 
the  variation  being  momentary  and  in  the  opposite  direction  to  the 
natural  currents;  and  are  similarly  known  as  the  currents  of  action. 
The  currents  of  action  are  propagated  in  both  directions  from  the  point 
of  the  application  of  the  stimulus,  and  are  of  momentary  duration. 

Rheoscopic  Frog. — This  negative  variation  may  be  demonstrated 


428  HANDBOOK    OF    PHYSIOLOGY. 

by  means  of  the  following  experiment. — The  new  current  produced  by 
stimulating  the  nerve  of  one  nerve-muscle  preparation  may  be  used  to 
stimulate  the  nerve  of  a  second  nerve-muscle  preparation.  The  foreleg 
of  a  frog  with  the  nerve  going  to  the  gastrocnemius  cut  long  is  placed 
upon  a  glass  plate,  and  arranged  in  such  way  that  its  nerve  touches  in 
two  places  the  sciatic  nerve,  exposed  but  preserved  in  situ,  in  the 
opposite  thigh  of  the  frog.  The  electrodes  from  an  induction  coil  are 
placed  behind  the  sciatic  nerve  of  the  second  preparation,  high  up.  On 
stimulating  it  with  a  single  induction  shock,  the  muscles  not  only  of  the 
same  leg  are  found  to  undergo  a  twitch,  but  also  those  of  the  first  prepa- 
ration, although  this  is  not  near  the  electrodes,  and  so  the  stimulation 
cannot  be  clue  to  an  escape  of  the  current  into  the  first  nerve.  This  ex- 
periment is  known  under  the  name  of  the  rheoscopic  frog. 

Nerve-stimuli. — Nerve-fibres  require  to  be  stimulated  before  they 
can  manifest  any  of  their  properties,  since  they  have  no  power  of  them- 
selves of  generating  force  or  of  originating  impulses.  The  stimuli  which 
are  capable  of  exciting  nerves  to  action,  are,  as  in  the  case  of  muscle, 
very  diverse.  They  are  very  similar  in  each  case.  The  mechanical, 
chemical,  thermal,  and  electric  stimuli  which  may  be  used  in  the  one 
case  are  also,  with  certain  differences  in  the  methods  employed,  effica- 
cious in  the  other.  The  chemical  stimuli  are  chiefly  these:  withdrawal 
of  water,  as  by  drying,  strong  solutions  of  neutral  salts  of  potassium, 
sodium,  etc.,  free  inorganic  acids,  except  phosphoric;  some  organic  acids; 
ether,  chloroform,  and  bile  salts.  The  electrical  stimuli  employed  are 
the  induction  and  continuous  currents  concerning  which  the  observations 
in  reference  to  muscular  contraction  should  be  consulted,  p.  406. 
Weaker  electrical  stimuli  will  excite  nerve  than  will  excite  muscle;  the 
nerve  stimulus  appears  to  gain  strength  as  it  descends,  and  a  weaker 
stimulus  applied  far  from  the  muscle  will  have  the  same  effect  as  a 
stronger  one  applied  to  the  nerve  near  the  muscle. 

It  will  be  only  necessary  here  to  add  some  account  of  the  effect  of  a 
constant  electrical  current,  such  as  that  obtained  from  DanielFs  battery, 
upon  a  nerve.  This  effect  may  be  studied  with  the  apparatus  described 
before.  A  pair  of  electrodes  are  placed  behind  the  nerve  of  the  nerve- 
muscle  preparation,  with  a  Du  Bois  Eeymond's  key  arranged  for  short 
circuiting  the  battery  current,  in  such  a  way  that  when  the  key  is 
opened  the  current  is  sent  into  the  nerve,  and  when  closed  the  current 
is  cut  off.  It  will  be  found  that  with  a  current  of  moderate  strength 
there  will  be  a  contraction  of  the  muscle  both  at  the  opening  and  at  the 
closing  of  the  key  (called  respectively  making  and  breaking  contrac- 
tions), but  that  during  the  interval  between  these  two  events  the  muscle 
remains  flaccid,  provided  the  battery  current  continues  of  constant  in- 
intensity.  If  the  current  be  a  very  weak  or  a  very  strong  one  the  effect 
is  not  quite  the  same;  one  or  other  of  the  contractions  may  be  absent. 
Which  of  these  contractions  is  absent  depends  upon  another  circum- 


THE    MUSCULAR    SYSTEM. 


429 


stance,  viz.,  the  direction  of  the  current.  The  direction  of  the  current 
may  be  ascending  or  descending;  if  ascending,  the  anode  or  positive- 
pole  is  nearer  the  muscle  than  the  kathode  or  negative  pole,  and  the 
current  to  return  to  the  battery  has  to  pass  up  the  nerve;  if  descend- 
ing, the  position  of  the  electrodes  is  reversed.  It  will  be  necessary 
before  considering  this  question  further  to  return  to  the  apparent  want 
of  effect  of  the  constant  current  during  the  interval  between  the  make 
and  break  contraction:  to  all  appearances  no  effect  is  produced  at  all, 
but  in  reality  a  very  important  change  is  brought  about  in  the  nerve  by 
the  passage  of  this  constant  (polarizing)  current.  This  may  be  shown  in 
two  ways,  first  of  all  by  the  galvanometer.  If  a  piece  of  nerve  be  taken, 
and  if  at  either  end  an  arrangement  be  made  to  test  the  electrical  condi- 
tion of  the  nerve  by  means  of  a  pair  of  non-polarizable  electrodes  con- 
nected with  a  galvanometer,  while  to  the  central  portion  a  pair  of  elec- 
trodes connected  with  a  Daniell's  battery  be  applied,  it  will  be  found  that 
natural  nerve-currents  are  profoundly  altered  on  the  passage  of  the  con- 


Fig.  301.— Diagram  illustrating  the  effects  of  curious  intensities  of  the  polarizing  currents,  n,  »'. 
nerve;  a.  anode;  k,  kathode;  the  curves  above  indicate  increase,  and  those  below  decrease  of 
irritability,  and  when  the  current  is  small  the  increase  and  decrease  are  both  small,  with  the  neutral 
point  near  a,  and  so  on  as  the  current  is  increased  in  strength. 

stant  current  in  the  neighborhood.  If  the  polarizing  current  be  in  the 
same  direction  as  the  latter  the  natural  current  is  increased,  but  if  in  the- 
direction  opposite  to  it,  the  natural  current  is  diminished.  This  change, 
produced  by  the  continual  passage  of  the  battery-current  through  a  por- 
tion of  the  nerve,  is  to  be  distinguished  from  the  negative  variation  of 
the  natural  current  to  which  allusion  has  been  already  made,  and  which 
is  a  momentary  change  occurring  on  the  sudden  application  of  the  stim- 
ulus. The  condition  produced  by  the  passage  of  a  constant  current  is 
known  by  the  name  of  Electrotonus. 

The  other  way  of  showing  the  effect  of  the  same  polarizing  current  is 
by  taking  a  nerve-muscle  preparation  and  applying  to  the  nerve  a  pair 
of  electrodes  from  an  induction  coil  whilst  at  a  point  further  removed 
from  the  muscle,  electrodes  from  a  Daniell's  battery  are  arranged  with  a 
key  for  short  circuiting  and  an  apparatus  (reverser)  by  which  the  bat- 
tery current  may  be  reversed  in  direction.  If  the  exact  point  be  ascer- 
tained to  which  the  secondary  coil  should  be  moved  from  the  primary 


430 


HANDBOOK    OF    PHYSIOLOGY. 


coil  in  order  that  a  minimum  contraction  be  obtained  by  the  induction 
shock,  and  the  secondary  coil  be  removed  slightly  from  the  primary,  the 
induction  current  cannot  now  produce  a  contraction;  but  if  the  polariz- 
ing current  be  sent  in  a  descending  direction,  that  is  to  say,  with  the 
kathode  nearest  the  other  electrodes,  the  induction  current,  which  was 
before  insufficient,  will  prove  sufficient  to  cause  a  contraction;  whereby 
indicating  that  with  a  descending  current  the  irritability  of  the  nerve  is 
increased.  By  means  of  a  somewhat  similar  experiment  it  may  be  shown 
that  an  ascending  current  will  diminish  the  irritability  of  a  nerve.  Sim- 
ilarly, if  instead  of  applying  the  induction  electrodes  below  the  other 
electrodes  they  are  applied  between  them,  like  effects  are  demonstrated, 
indicating  that  in  the  neighborhood  of  the  kathode  the  irritability  of  the 
nerve  is  increased  by  a  constant  current,  and  in  the  neighborhood  of  the 
anode  diminished.  This  increase  in  irritability  is  called  Tcathelectrotonus, 
and  similarly  the  decrease  is  called  anelectrotonus.  As  there  is  between 
the  electrodes  both  an  increase  and  a  decrease  of  irritability  on  the  pas- 
sage of  a  polarizing  current,  it  must  be  evident  that  the  increase  must 
shade  off  into  the  decrease,  and  that  there  must  be  a  neutral  point  where 
there  is  neither  increase  nor  decrease  of  irritability.  The  position  of  the 
neutral  point  is  found  to  vary  with  the  intensity  of  the  polarizing  cur- 
rent— when  the  current  is  weak  the  point  is  nearer  the  anode,  when 
strong  nearer  the  kathode  (Fig.  301);  when  a  constant  current  passes 
into  a  nerve,  therefore,  if  a  contraction  result,  it  may  be  assumed  that 
it  is  due  to  the  increased  irritability  produced  in  the  neighborhood  of 
the  kathode,  but  the  breaking  contraction  must  be  produced  by  a  rise  in 
irritability  from  a  lowered  state  to  the  normal  in  the  neighborhood  of 
the  anode.  The  contractions  produced  in  the  muscle  of  a  nerve-muscle 
preparation  by  a  constant  current  have  been  arranged  in  a  table  which 
is  known  as  Pfliiger's  Law  of  Contractions.  It  is  really  only  a  state- 
ment as  to  when  a  contraction  may  be  expected: — 


Descending  Current. 

Ascending  Current. 

Make. 

Break. 

Make. 

Break. 

Weak 

Yes. 

No. 

Yes. 

No. 

Moderate 

Yes. 

Yes. 

Yes. 

Yes. 

Yes. 

No. 

No. 

Yes. 

The  difficulty  in  this  table  is  chiefly  in  the  effect  of  a  weak  current, 
but  the  following  statement  will  explain  it.  The  increase  of  irritability 
at  the  kathode  is  more  potent  to  produce  a  contraction  than  the  rise  of 
irritability  at  the  anode,  and  so  with  weak  currents  the  only  effect  is  a 
contraction  at  the  make  of  both  currents,  and  the  descending  current  is 


THE    MUSCULAR    SYSTEM.  431 

more  potent  than  the  ascending  (and  with  still  weaker  currents  is  the 
only  one  which  produces  any  effect),  since  the  kathode  is  near  the  mus- 
cle; whereas  in  the  case  of  the  ascending  current  the  stimulus  has  to 
pass  through  a  district  of  diminished  irritability,  which  with  a  very 
strong  current  acts  as  a  block,  but  with  a  weak  only  slightly  affects  the 
contraction.  As  the  current  is  stronger  recovery  from  anelectrotonus 
is  able  to  produce  a  contraction  as  well  as  kathelectrotonus,  a  contrac- 
tion occurs  both  at  the  make  and  the  break  of  the  current.  The  absence 
of  contraction  with  a  very  strong  current  at  the  break  of  the  ascending 
current  may  be  explained  by  supposing  that  the  region  of  fall  in  irrita- 
bility at  the  kathode  blocks  the  stimulus  of  the  rise  in  irritability  a 
the  anode. 

Thus  we  have  seen  that  two  circumstances  influence  the  effect  of  the 
constant  current  upon  the  nerve,  viz.,  the  strength  and  direction  of  the 
current.  It  is  also  necessary  that  the  stimulus  should  be  applied  sud- 
denly and  not  gradually,  and  that  the  irritability  of  the  nerve  be  normal 
and  not  increased  or  diminished.  Sometimes  (when  the  nerve  is  spe- 
cially irritable  ?)  instead  of  a  simple  contraction  a  tetanus  occurs  at  the 
make  or  break  of  the  constant  current.  This  is  especially  liable  to  oc- 
cur at  the  break  of  a  strong  ascending  current  which  has  been  passing 
for  some  time  into  the  preparation;  this  is  called  Ritter's  tetanus,  and 
may  be  increased  by  passing  a  current  in  an  opposite  direction  or  stopped 
by  passing  a  current  in  the  same  direction. 


CHAPTER  XV. 

NUTRITION ;  THE  INCOME  AND  EXPENDITURE  OF  THE  HUMAN 

BODY. 

The  various  physiological  processes  which  occur  in  the  human  body 
have,  with  the  exception  of  those  in  the  nervous  and  generative  systems, 
which  will  be  considered  in  succeeding  chapters,  now  been  dealt  with, 
and  it  will  be  as  well  to  give  in  this  chapter  a  summary  of  what  has 
been  considered  more  at  length  before. 

The  subject  may  be  considered  under  the  following  heads.  (1.)  The 
Evidence  and  Amount  of  Expenditure.  (2.)  The  Sources  and  Amount 
of  Income.     (3.)  The  Sources  and  Objects  of  Expenditure. 

1.  Evidence  and  Amount  of  Expenditure. — There  is  complete 
evidence  of  Expenditure  by  the  living  body. 

From  the  table  (p.  208)  it  will  be  seen  how  the  various  amounts  of 
the  excreta  are  calculated. 

a.  From  the  Lungs  there  is  exhaled  every  24  hours, 

Of  Carbonic  Acid,  about      .         .         .       15,000  grains. 
Of  Water,  .....  5,000       " 

Traces  of  organic  matter. 

b.  From  the  Skin — 

Water, 11,500  grains. 

Solid  and  gaseous  matter,     .         .         .  250       " 

c.  From  the  Kidneys — 

Water, 23,000  grains. 

Organic  matter, 680       " 

Minerals  and  salines,       ....         420       " 

d.  From  the  Intestines — 

Water, 2,000  grains. 

Various  organic  and  mineral  substances,         800      " 

In  the  account  of  Expenditure,  must  be  remembered  in  addition  the 
milk  (during  the  period  of  suckling),  and  the  products  of  secretion  from 
the  generative  organs  (ova,  menstrual  blood,  semen);  but,  from  their 
variable  and  uncertain  amounts,  these  cannot  be  reckoned  with  the  pre- 
ceding. 

Altogether,  the  expenditure  of  the  body  represented  by  the  sum  of 
these  various  excretory  products  amounts  every  24  hours  to— 


INCOME    AND    EXPENDITURE    OF    BODY.  433 

Solid  and  gaseous  mutter,     .         .         .     17,150  grains  (1,113  grms.) 
Water  (either  fluid  or  combined  with  the 
solids  and  gaseous  matter),     .         .         49,500       "     (2,695       "    ) 

The  matter  thus  lost  by  the  body  is  matter  the  chemical  attractions 
of  which  have  been  in  great  part  satisfied;  and  which  remains  quite  use- 
less as  food,  until  its  elements  have  been  again  separated  and  re-arranged 
by  members  of  the  vegetable  world.  It  is  especially  instructive  to  com- 
pare the  chemical  constitution  of  the  products  of  expenditure,  thus 
separated  by  the  various  excretory  organs,  with  that  of  the  sources  of 
income  to  be  immediately  considered.  It  is  evident  from  these  facts 
that  if  the  human  body  is  to  maintain  its  size  and  composition,  there 
must  be  added  to  it  matter  corresponding  in  amount  with  that  which  is 
lost.     The  income  must  equal  the  expenditure. 

2.  Sources  and  Amount  of  Income. — The  Income  of  the  body 
consists  partly  of  Food  and  Drink,  and  partly  of  Oxygen. 

Into  the  stomach  there  is  received  daily: — 

Solid  (chemically  dry)  food,      .         .         .     8,000  grains  (520  grms.) 
Water  (as  water,  or  variously  combined 
with  solid  food),       ....  35,000-40,000  "  (2,444  "     ) 

By  the  Lungs  there  is  absorbed  daily: — 

Oxygen, 13,000  "       (844  "     ) 

The  average  total  daily  receipts,  in  the  shape  of  food,  drink  and  oxy- 
gen, correspond,  therefore,  with  the  average  total  daily  expenditure,  as 
shown  by  the  following  table. 


Income. 
Solid  food,      .         .     8,000  grains. 
Water,       .         .         37,650     " 
Oxygen,  .         .    13,000     " 


58,650  grains. 
(3,808  grms.,  or  about  8-J-  lb.) 


Expenditure. 
Lungs,         .         .       20,000  grains. 
Skin,      .         .         .  11,750     " 
Kidneys,     ,         .       24,100      " 
Intestines,      .         .     2,800      " 
(Generative  and  mam- 
mary-gland products 
are    supposed   to   be 
included) 


58,650  grains. 
(about  3,808  grms.) 

These  quantities  are  approximate  only.  But  they  may  be  taken  as 
fair  averages  for  a  healthy  adult.  The  absolute  identity  of  the  two  num- 
bers (in  grains)  in  the  two  tables  is  of  course  diagrammatic.  No  such 
exactitude  in  the  account  occurs  in  any  living  body,  in  the  course  of  any 
given  twenty-four  hours.  But  any  difference  which  exists  between  the 
two  amounts  of  income  and  expenditure  at  any  given  period,  corresponds 

•vO 


434  HANDBOOK    OF    PHYSIOLOGY. 

merely  with  the  slight  variations  in  the  amount  of  capital  (weight  of 
body)  to  which  the  healthiest  subject  is  liable. 

The  chemical  composition  of  the  food  (p.  209)  may  be  profitably  com- 
pared with  that  of  the  excreta,  as  before  mentioned.  The  greater  part 
of  our  food  is  composed  of  matter  which  contains  much  potential  energy; 
and  in  the  chemical  changes  (combustion  and  other  processes)  to  which 
it  is  subject  in  the  body,  active  energy  is  manifested. 

3.  The  Sources  and  Objects  of  Expenditure. — The  sources  of 
the  necessary  waste  and  expenditure  in  the  living  body  are  various  and 
extensive.     They  may  be  comprehended  under  the  following  heads: — 

(1)  Common  wear  and  tear;  such  as  that  to  which  all  structures,  liv- 
ing and  not  living,  are  subjected  by  exposure  and  work;  but  which  must 
be  especially  large  in  the  soft  and  easily  decaying  structures  of  an  animal 
body. 

(2)  Manifestations  of  Force  in  the  form  either  of  Heat  or  Motion.  In 
the  former  case  (Heat),  the  combustion  must  be  sufficient  to  maintain  a 
temperature  of  about  100°  F.  (37.8°  C.)  throughout  the  whole  substance 
of  the  body,  in  all  varieties  of  external  temperature,  notwithstanding  the 
large  amount  continually  lost  in  the  ways  previously  enumerated.  In 
the  case  of  Motion,  there  is  the  expenditure  involved  in  the  (a)  Ordinary 
muscular  movements,  as  in  Prehension,  Mastication,  Locomotion,  and 
numberless  other  ways:  as  well  as  in  (b)  Various  involuntary  movements, 
as  in  Eespiration,  Circulation,  Digestion,  etc. 

(3)  Manifestation  of  Nerve  Force;  as  in  the  general  regulation  of  all 
physiological  processes,  e.  g.,  Eespiration,  Circulation,  Digestion;  and  in 
Volition  and  all  other  manifestations  of  cerebral  activity. 

(4)  The  energy  expended  in  all  physiological  processes,  e.g.,  Nutrition, 
Secretion,  Growth,  and  the  like. 

The  total  expenditure  or  total  manifestation  of  energy  by  an  animal 
body  can  be  measured,  with  fair  accuracy;  the  terms  used  being  such  as 
are  employed  in  connection  with  other  than  vital  operations.  All  state- 
ments, however,  must  be  considered  for  the  present  approximate  only, 
and  especially  is  this  the  case  with  respect  to  the  comparative  share  of 
expenditure  to  be  assigned  to  the  various  objects  just  enumerated. 

The  amount  of  energy  daily  manifested  by  the  adult  human  body  in 
(a)  the  maintenance  of  its  temperature;  (b)  in  internal  mechanical  work, 
as  in  the  movements  of  the  respiratory  muscles,  the  heart,  etc. ;  and  (c) 
in  external  mechanical  work,  as  in  locomotion  and  all  other  voluntary 
movements,  has  been  reckoned  at  about  3,400  foot-tons.  Of  this  amount 
only  one-tenth  is  directly  expended  in  internal  and  external  mechanical 
work;  the  remainder  being  employed  in  the  maintenance  of  the  body's 
heat.  The  latter  amount  represents  the  heat  which  would  be  required 
to  raise  48.4  lb.  of  water  from  the  freezing  to  the  boiling  point;  or  if 


INCOME    AND    EXPENDITURE    OF    BODY.  435 

converted  into  mechanical  power,  it  would  suffice  to  raise  the  body  of  a 
man  weighing  about  150  lb.  through  a  vertical  height  of  8£  miles. 

To  the  foregoing  amounts  of  expenditure  must  be  added  the  quite 
unknown  quantity  expended  in  the  various  manifestations  of  nerve-force, 
and  in  the  work  of  nutrition  and  growth  (using  these  terms  in  their 
widest  sense).  By  comparing  the  amount  of  energy  which  should  be 
produced  in  the  body  from  so  much  food  of  a  given  kind,  with  that 
which  is  actually  manifested  (as  shown  by  the  various  products  of  com- 
bustion, in  the  excretions)  attempts  have  been  made,  indeed,  to  estimate, 
by  a  process  of  exclusion,  these  unknown  quantities;  but  all  such 
calculations  must  be  at  present  considered  only  very  doubtfully  ajDproxi- 
mate. 

Sources  of  Error. — Among  the  sources  of  error  in  any  such  calcula- 
tions must  be  reckoned,  as  a  chief  one,  the,  at  present,  entirely  unknown 
extent  to  which  forces  external  to  the  body  (mainly  heat)  can  be  utilized 
by  the  tissues.  We  are  too  apt  to  think  that  the  heat  and  light  of  the 
sun  are  directly  correlated,  as  far  as  living  beings  are  concerned,  with 
the  chemico-vital  transformations  involved  in  the  nutrition  and  growth 
of  the  members  of  the  vegetable  world  only.  But  animals,  although 
comparatively  independent  of  external  heat  and  other  forces,  probably 
utilize  them,  to  the  degree  occasion  offers.  And  although  the  correlative 
manifestation  of  energy  in  the  body,  due  to  external  heat*  and  light,  may 
still  be  measured  in  so  far  as  it  may  take  the  form  of  mechanical  work; 
yet,  in  so  far  as  it  takes  the  form  of  expenditure  in  nutrition  or  nerve- 
force,  it  is  evidently  impossible  to  include  it  by  any  method  of  estima- 
tion yet  discovered;  and  all  accounts  of  it  must  be  matters  of  the  purest 
theory.  These  considerations  may  help  to  explain  the  apparent  discrep- 
ancy between  the  amount  of  energy  which  is  capable  of  being  produced 
by  the  usual  daily  amount  of  food,  with  that  which  is  actually  manifested 
daily  by  the  body;  the  former  leaving  but  a  small  margin  for  anything 
beyond  the  maintenance  of  heat,  and  mechanical  work. 

In  the  foregoing  sketch  we  have  supposed  that  the  excreta  are  exactly 
replaced  by  the  ingesta. 

Nitrogenous  Equilibrium  and  Formation  of  Fat. — If  an  animal, 
however,  which  has  undergone  a  starving  period,  be  fed  upon  a  diet  of 
lean  meat  it  is  found  that  instead  of  the  greater  part  of  the  nitrogen 
being  stored  up,  as  one  would  expect,  the  chief  part  of  it  appears  in  the 
urine  as  urea,  and  continuing  with  the  diet  the  excreted  nitrogen  ap- 
proximates more  and  more  closely  to  the  ingested  nitrogen  until  at  last 
the  amounts  are  equal  in  both  cases.  This  is  called  nitrogenous  equilib- 
rium. There  may,  however,  be  an  increase  of  weight  which  is  due  to 
the  putting  on  of  fat.  If  this  is  the  case  it  must  be  apparent  that  the 
protoplasm  of  the  tissues  is  able  to  form  fat  out  of  proteid  material 
and  to  split  it  up  into  urea  and  fat.     If  fat  be  given  in  small  quantities 


436  HANDBOOK    OF    PHYSIOLOGY. 

with  the  meat,  for  a  time  the  carbon  of  the  egesta  and  ingestaare  equal,. 
but  if  the  fat  be  increased  beyond  a  certain  point  the  body  weight  in- 
creases from  a  deposition  of  fat;  not,  however,  by  a  mere  mechanical 
deposition  or  nitration  from  the  blood,  but  by  an  actual  act  of  secretion 
by  the  protoplasm  whereby  the  fat  globules  are  stored  up  within  itself: 
similarly  as  regards  carbo-hydrates,  if  they  are  in  small  quantity,  the 
carbon  appears  in  the  excreta,  but  beyond  a  certain  amount  a  consider- 
able portion  of  it  is  retained  in  fat;  having  been  by  the  protoplasm 
stored  up  within  itself  in  that  material.  The  amount  of  proteid  material 
required  to  produce  nitrogenous  equilibrium  is  considerable,  but  it  may 
be  materially  diminished  by  the  addition  of  carbo-hydrate  or  fatty  food, 
or  of  gelatin  to  the  exclusively  meat  diet. 

It  is  of  much  interest  to  consider  how  the  protoplasm  acts  in  con- 
verting food  into  energy  and  decomposition  products,  since  the  sub- 
stance itself  does  not  undergo  much  change  in  the  process  except  a  slight. 
amount  of  wear  and  tear.  We  may  assume  that  it  is  the  property  of 
protoplasm  to  separate  from  the  blood  the  materials  which  it  may  re- 
quire to  produce  secretions,  in  the  case  of  the  protoplasm  of  secreting 
glands,  or  to  enable  it  to  evolve  heat  and  energy,  as  in  the  case  of  the 
protoplasm  of  muscle.  The  substances  are  very  possibly  different  for 
each  process,  and  the  decomposition  products,  too,  may  be  different  in 
quality  or  quantity.  Proteid  materials  appear  to  be  specially  needed,  as 
is  shown  by  the  invariable  presence  of  urea  in  the  urine  even  during- 
starvation;  and  as  in  the  latter  case,  there  has  been  no  food  from  which 
these  materials  could  have  been  derived,  the  urea  is  considered  to  be  de- 
rived from  the  disintegration  of  the  nitrogenous  tissues  themselves.  The 
removal  of  all  fat  from  the  body  in  a  starvation  period,  as  the  first  ap- 
parent change,  would  lead  to  the  supposition  that  fat  is  also  a  specially 
necessary  pabulum  for  the  production  of  protoplasmic  energy;  and  the 
fact  that,  as  mentioned  above,  with  a  diet  of  lean  meat  an  enormous 
amount  appears  to  be  required,  suggests  that  in  that  case  protoplasm  ob- 
tains the  fat  it  needs  from  the  proteid  food,  which  process  must  be  evi- 
dently a  source  of  much  waste  of  nitrogen.  The  idea  that  proteid  food 
has  two  destinations  in  the  economy,  viz.,  to  form  organ  or  tissue  proteid 
which  builds  up  organs  and  tissues,  and  circulating  proteid,  from  which 
the  organs  and  tissues  derive  the  materials  of  their  secretions,  or  for  pro- 
ducing their  energy,  is  a  convenient  one,  and  it  is  unlikely  that  proto- 
plasm would  go  to  the  expense  of  construction  simply  for  the  sake  of 
immediate  destruction. 


CHAPTER   XVI. 


THE  VOICE  AND   SPEECH. 


The  Larynx.  — In  nearly  all  air-breathing  vertebrate  animals  there 
are  arrangements  for  tbe  production  of  sound,  or  voice,  in  some  parts  of 
the  respiratory  apparatus.  In  many  animals,  the  sound  admits  of  being 
variously  modified  and  altered  during  and  after  its  production;  and,  in 


Coniu  min 
Cornu  maj: 


Coruu  soet" 


Ug;  crica-thyivmedi 

Carts  cricoidea, 
Xig;  erica-tracheae. 


__ ,w«  Stcmo-hyoideus. 


'•nit  StcmQ-hyoideil5. 


Stemo-hyoideTia. 
Crico-thiroideaat 


Cart:  tracheale 


Fig.  302.— The  Larynx,  as  seen  from  the  front,  showing  the  cartilages  and  ligaments, 
muscles,  with  the  exceptions  of  one  crico-thyroid,  are  cut  off  short.    (Stoerk.) 


The 


man,  one  such  modification  occurring  in  obedience  to  dictates  of  the 
cerebrum,  is  speech. 

It  has  been  proved  by  observations  on  living  subjects,  by  means  of 
tbe  laryngoscope  (p.  441),  as  well  as  by  experiments  on  the  larynx  taken 
from  the  dead  body,  that  the  sound  of  the  human  voice  is  the  result  of 
the  vibration  of  the  inferior  laryngeal  ligaments,  or  true  vocal  cords  (A, 
cv,  Fig.  307)  which  bound  the  glottis,  caused  by  currents  of  expired  air 
impelled  over  their  edges.  If  a  free  opening  exists  in  the  trachea,  the 
sound  of  the  voice  ceases,  but  it  returns  if  the  opening  is  closed.  An 
opening  into  the  air-passages  above  the  glottis,  on  the  contrary,  does  not 
prevent  the  voice  being  produced.  By  forcing  a  current  of  air  through 
the  larynx  in  the  dead  subject,  clear  vocal  sounds  are  elicited,  though 


438 


HANDBOOK   OF    PHYSIOLOGY 


the  epiglottis,  the  upper  ligaments  of  the  larynx  or  false  vocal  cords,, 
the  ventricles  between  them  and  the  inferior  ligaments  or  true  vocal 
cords,  and  the  upper  part  of  the  arytenoid  cartilages,  be  all  removed; 
provided  the  true  vocal  cords  remain  entire,  with  their  points  of  attach- 
ment, and  be  kept  tense  and  so  approximated  that  the  fissure  of  the  glot- 
tis may  be  narrow. 

The  vocal  ligaments  or  cords,  therefore,  are  regarded  as  the  proper 
organs  for  the  production  of  vocal  sounds:  the  modifications  of  these 
sounds  being  effected,  as  will  be  presently  explained,  by  other  parts — 
tongue,  teeth,  lips,  etc..  as  well  as  by  them.  The  structure  of  the  vocal 
cords  is  adapted  to  enable  them  to  vibrate  like  tense  membranes,  for 
they  are  essentially  composed  of  elastic  tissue;  and  they  are  so  attached 


ixg.  Aryi^epl^Iot^ 


Cart.  "WxisDergii 
Cart.  SantorinL 

Cart,  aryten. 
Iroc.  nmsciil.  _, 

Jfig.  crlfSJ-aryteri. 
ISg,  eerata^tfco.-pgst,  isup, 

Corxrjiiiif erL.  _ 

Tig,  carat-erica,  joat. inf .  .. 


Cart,  traclu'ic-l-     >    _:Ju 


J?ars  mem"bran. 


Fig.  303.— The  larynx  as  seen  from  behind  after  removal  of  the  muscles, 
ligaments  only  remain.    (Stoerk.) 


The  cartilages  and 


to  the  cartilaginous  parts  of  the  larynx  that  their- position  and  tension 
can  be  variously  altered  by  the  contraction  of  the  muscles  which  act  on 
these  parts. 

Thus  it  will  be  seen  that  the  larynx  is  the  organ  of  voice.  It  may 
be  said  to  consist  essentially  of  the  two  vocal  cords  and  the  various  car- 
tilaginous, muscular,  and  other  apparatus  by  means  of  which  not  only 
can  the  aperture  of  the  larynx  (rima  glottidis),  of  which  they  are  the 
lateral  boundaries,  be  closed  against  the  entrance  and  exit  of  the  air  to' 
or  from  the  lungs,  but  also  by  means  of  which  the  cords  themselves  can 
be  stretched  or  relaxed,  shortened  or  lengthened,  in  accordance  with  the 
conditions  that  may  be  necessary  for  the  air  in  passing  over  them,  to  set 
them  vibrating  and  produce  various  sounds.  Their  action  in  respiration 
has  been  already  referred  to. 


THE    VOICE    AXD    SPEECH.  439 

Anatomy  of  the  Larynx. — The  principal  parts  entering  into  the 
formation  of  the  larynx  (Figs.  302  and  303)  are — the  thyroid  cartilage; 
the  cricoid  cartilage;  the  two  arytenoid  cartilages;  and  the  two  true  vocal 
oords  (Fig.  307).  The  epiglottis  (Fig.  303)  has  but  little  to  do  with  the 
voice,  and  is  chiefly  useful  in  protecting  the  upper  part  of  the  larynx 
from  the  entrance  of  food  and  drink  in  deglutition.  It  also  probably 
guides  mucus  or  other  fluids  in  small  amount  from  the  mouth  around 
the  sides  of  the  upper  opening  of  the  glottis  into  the  pharynx  and  oeso- 
phagus, thus  preventing  them  from  entering  the  larynx.  The  false 
vocal  cords  (cvs,  Fig.  307),  and  the  ventricle  of  the  larynx,  which  is  a 
space  between  the  false  and  the  true  cord  of  either  side,  need  be  here  only 
referred  to. 

Cartilages. — (a)  The  thyroid  cartilage  (Fig.  304,  1  to  4)  does  not 
form  a  complete  ring  around  the  larynx,  but  only  covers  the  front  por- 
tion, (b)  The  cricoid  cartilage  (Fig.  304,  5,  6),  on  the  other  hand,  is  a 
complete  ring;  the  back  part  of  the  ring  being  much  broader  than  the 
front.  On  the  top  of  this  broad  portion  of  the  cricoid  are  (c)  the  aryte- 
noid cartilages  (Fig.  304,  7),  the  connection  between  the  cricoid  below 
and  arytenoid  cartilages  above  being  a  joint  with  synovial  membrane  and 
ligaments,  the  latter  permitting  tolerably  free  motion  between  them.  But 
although  the  arytenoid  cartilages  can  move  on  the  cricoid,  they  of  course 
accompany  the  latter  in  all  its  movements,  just  as  the  head  may  nod  or 
turn  on  the  top  of  the  spinal  column,  but  must  accompany  it  in  all  its 
movements  as  a  whole. 

Joints  and  Ligaments. — The  thyroid  cartilage  is  also  connected 
with  the  cricoid,  not  only  by  ligaments,  but  also  by  joints  with  synovial 
membranes;  the  lower  cornua  of  the  thyroid  clasping,  or  nipping,  as  it 
were,  the  cricoid  between  them,  but  not  so  tightly  but  that  the  thyroid 
can  revolve,  within  a  certain  range,  around  an  axis  passing  transversely 
through  the  two  joints  at  which  the  cricoid  is  clasped.  The  vocal  cords 
are  attached  (behind)  to  the  front  portion  of  the  base  of  the  arytenoid 
cartilages,  and  (in  front)  to  the  re-entering  angle  at  the  back  part  of  the 
thyroid;  it  is  evident,  therefore,  that  all  movements  of  either  of  these 
cartilages  must  produce  an  effect  on  them  of  some  kind  or  other.  Inas- 
much, too,  as  the  arytenoid  cartilages  rest  on  the  top  of  the  back  portion 
of  the  cricoid  cartilage,  and  are  connected  with  it  by  capsular  and  other 
ligaments,  all  movements  of  the  cricoid  cartilage  must  move  the  aryte- 
noid cartilages,  and  also  produce  an  effect  on  the  vocal  cords. 

Intrinsic  Muscles. — The  so-called  intrinsic  muscles  of  the  larynx, 
or  those  which,  in  their  action,  have  a  direct  action  on  the  vocal  cords, 
are  nine  in  number — four  pairs,  and  a  single  muscle;  namely,  two 
crico-thyroid  muscles,  two  thyro-arytenoid,  two  posterior  crico-arytenoid, 
two  lateral  crico-arytenoid  and  one  arytenoid  muscle.  Their  actions  are 
as  follows: — When  the  crico-thyroid  muscles  (10,  Fig.  306)  contract,  they 
rotate  the  cricoid  on  the  thyroid  cartilage  in  such  a  manner,  that  the 
upper  and  back  part  of  the  former,  and  of  necessity  the  arytenoid  car- 
tilages on  top  of  it,  are  tipped  backwards,  while  the  thyroid  is  inclined 
forward;  and  thus,  of  course,  the  vocal  cords  being  attached  in  front  to 
one,  and  behind  to  the  other,  are  "put  on  the  stretch." 

The  thyro-arytenoid  muscles,  on  the  other  hand,  have  an  opposite 
action — pulling  the  thyroid  backwards,  and  the  arytenoid  and  upper 
back  part  of  the  cricoid  cartilages  forwards,  and  thus  relaxing  the  vocal 
cords. 


44:0 


HANDBOOK    OF    PHYSIOLOGY. 


The  crico-arytenoidei  postici  muscles  (Fig.  303)  dilate  the  glottis, 
and  separate  the  vocal  cords,  the  one  from  the  other,  by  an  action  on 
the  arytenoid  cartilage.  By  their  contraction  they  tend  to  pull  together 
the  outer  angles  of  the  arytenoid  cartilages  in  such  a  fashion  as  to  rotate 
the  latter  at  their  joint  with  the  cricoid,  and  of  course  to  throw  asunder 
their  anterior  angles  to  which  the  vocal  cords  are  attached. 

These  posterior  crico-arytenoid  muscles  are  opposed  by  the  crico-ary- 
tenoidei laterales,  which,  pulling  in  the  opposite  direction  from  the  other 
side  of  the  axis  of  rotation,  have  of  course  exactly  the  opposite  effect, 
and  close  the  glottis. 

The  aperture  of  the  glottis  can  be  also  contracted  by  the  arytenoid 
muscle  (Fig.  305),  which,  in  its  contraction,  pulls  together  the  upper 
parts  of  the  arytenoid  cartilages  between  which  it  extends. 

Nerve  Supply. — In  the  performance  of  the  functions  of  the  larynx 
the  sensory  filaments  of  the  superior  laryngeal  branch  of  the  vagi  sup- 


15&W7  wigJottoj 


Csail"Wrisbergu*( 


Cart,  SantoririL4p 


Fig.  304. 


tn,  CMco-arytenoid.  post,  - 

Coma  inferior 1 

XigV  cerato^cric. 

J&ra  pesfc.forf.  ineiribiariL. — 

£ara.  rarfflag. 

Fig.  305. 


Fig.  304.— Cartilages  of  the  larynx  seen  from  the  front.  lto4,  thyroid  cartilage;  1,  vertical 
ridge  or  pomum  Adami;  2,  right  ala;  3,  superior,  and  4,  inferior  cornu  of  the  right  side;  5,  6,  cricoid 
cartilage ;  5,  inside  of  the  posterior  part ;  6,  anterior  narrow  part  of  the  ring ;  7,  arytenoid  cartilages. 

Fig.  305.— The  larynx  as  seen  from  behind.    To  show  the  intrinsic  muscles  posteriorly.  (Stoerk  ) 

ply  that  acute  sensibility  by  which  the  glottis  is  guarded  against  the  in- 
gress of  foreign  bodies,  or  of  irrespirable  gases.  The  contact  of  these 
stimulates  the  nerve  filaments;  and  the  impression  conveyed  to  the 
medulla  oblongata,  whether  it  produce  sensation  or  not,  is  reflected  to 
the  filaments  of  the  recurrent  or  inferior  laryngeal  branch,  and  excites 
contraction  of  the  muscles  that  close  the  glottis.  Both  these  branches 
of  pneumogastric  co-operate  also  in  the  production  and  regulation  of  the 
voice;  the  inferior  laryngeal  determining  the  contraction  of  the  muscles 
that  vary  the  tension  of  the  vocal  cords,  and  the  superior  laryngeal  con- 
veying to  the  mind  the  sensation  of  the  state  of  these  muscles  necessary 
for  their  continuous  guidance.  And  both  the  branches  co-operate  in 
the  actions  of  the  larynx  in  the  ordinary  slight  dilatation  and  contrac- 
tion of  the  glottis  in  the  acts  of  expiration  and  inspiration,  and  more 


THE    VOICE    AND    SPEECH.  441 

evidently  in  those  of  coughing  and  other  foreible  respiratory  move- 
ments. 

The  laryngoscope  is  an  instrument  employed  in  investigating  dur- 
ing life  the  condition  of  the  pharynx,  larynx,  and  trachea.  It  consists 
of  a  large  concave  mirror  with  perforated  centre,  and  of  a  smaller  mir- 
ror fixed  in  a  long  handle.  It  is  thus  used:  the  patient  is  placed  in  a 
chair,  a  good  light  (argand  burner,  or  lamp)  is  arranged  on  one  side  of. 
and  a  little  above  his  head.  The  operator  fixes  the  large  mirror  round 
his  head  in  such  a  manner,  that  he  looks  through  the  central  aperture 
with  one  eye.  He  then  seats  himself  opposite  the  patient,  and  so  alters 
the  position  of  the  mirror,  which  is  for  this  purpose  provided  with  a  ball 
and  socket  joint,  that  a  beam  of  light  is  reflected  on  the  lips  of  the  pa- 
tient. 

The  patient  is  now  directed  to  throw  his  head  slightly  backwards, 
and  to  open  his  mouth;  the  reflection  from  the  mirror  lights  up  the 
cavity  of  the  mouth,  and  by  a  little  alteration  of  the  distance  between 
the  operator  and  the  patient  the  point  at  which  the  greatest  amount  of 
light  is  reflected  by  the  mirror — in  other  words  its  focal  length — is 
readily  discovered.  The  small  mirror  fixed  in  the  handle  is  then 
warmed,  either  by  holding  it  over  the  lamp,  or  by  putting  it  into  a  ves- 
sel of  warm  water;  this  is  necessary  to  prevent  the  condensation  of 
breath  upon  its  surface.  The  degree  of  heat  is  regulated  by  applying 
the  back  of  the  mirror  to  the  hand  or  cheek,  when  it  should  feel  warm 
without  being  painful. 

After  these  preliminaries  the  patient  is  directed  to  put  out  his  tongue, 
which  is  held  by  the  left  hand  gently  but  firmly  against  the  lower  teeth, 
by  means  of  a  handkerchief.  The  warm  mirror  is  passed  to  the  back  of 
the  mouth,  until  it  rests  upon  and  slightly  raises  the  base  of  the  uvula, 
and  at  the  same  time  the  light  is  directed  upon  it:  an  inverted  image  of 
the  larynx  and  trachea  will  be  seen  in  the  mirror.  If  the  dorsum  of  the 
tongue  be  alone  seen,  the  handle  of  the  mirror  must  be  slightly  lowered 
until  the  larynx  comes  into  view;  care  should  be  taken,  however,  not  to 
move  the  mirror  upon  the  uvula,  as  it  excites  retching.  The  observa- 
tion should  not  be  prolonged,  but  should  rather  be  repeated  at  short  in- 
tervals. 

The  structures  seen  will  vary  somewhat  according  to  the  condition  of 
the  parts  as  to  inspiration,  expiration,  phonation.  etc.;  they  are  (Figs. 
30?)  first,  and  apparently  at  the  posterior  part,  the  base  of  the  tongue, 
immediately  below  which  is  the  arcuate  outline  of  the  epiglottis,  with 
its  cushion  or  tubercle.  Then  are  seen  in  the  central  line  the  true  vocal 
cords,  white  and  shining  in  their  normal  condition.  The  cords  approxi- 
mate (in  the  inverted  image)  posteriorly;  between  them  is  left  a  chink, 
narrow  whilst  a  high  note  is  being  sung,  wide  during  a  deep  inspiration. 
On  each  side  of  the  true  vocal  cords,  and  on  a  higher  level,  are  the  pink 
false  vocal  cords.  Still  more  externally  than  the  false  vocal  cords  is  the 
aryteno-epiglottidean  fold,  in  which  are  situated  upon  each  side  three 
small  elevations;  of  these  the  most  external  is  the  cartilage  of  Wrisberg, 
the  intermediate  is  the  cartilage  of  Santorini.  whilst  the  summit  of  the 
arytenoid  cartilage  is  in  front,  and  somewhat  below  the  preceding,  being 
only  seen  during  deep  inspiration.  The  rings  of  the  trachea,  and  even 
the  bifurcation  of  the  trachea  itself,  if  the  patient  be  directed  to  draw  a 
deep  breath,  may  be  seen  in  the  interval  between  the  true  vocal  cords. 


442 


HANDBOOK    OF    PHYSIOLOGY. 


Movements  of  the  Vocal  Cords. — The  placing  of  the  vocal  cords 
in  a  position  parallel  one  with  the  other,  is  effected  by  a  combined  action 
of  the  various  intrinsic  muscles  "which  act  on  them — the  thyro-arytenoi- 
dei  having,  without  much  reason,  the  credit  of  taking  the  largest  share 
in  the  production  of  this  effect.  Fig.  307  is  intended  to  show  the 
various  positions  of  the  vocal  cords  under  different  circumstances.  Thus, 
in  ordinary  tranquil  breathing,  the  opening  of  the  glottis  is  wide  and 
triangular  (b),  becoming  a  little  wider  at  each  inspiration,  and  a  little 
narrower  at  each  expiration.  On  making  a  rapid  and  deep  inspiration 
the  opening  of  the  glottis  is   widely  dilated  (as  in  c),  and  somewhat 


Fig.  306.  Fig.  307. 

Fig.  306.-Lateral  view  of  exterior  of  the  larynx  8,  thyroid  cartilage;  9,  cricoid  cartilage;  10, 
crico-thyroid  muscle;  11,  crico-thyroid  ligament;  12,  first  rings  of  trachea.    (Willis.) 

Fig.  307.— Three  laryngoscopy  views  of  the  superior  aperture  of  the  larynx  and  surrounding 
parts.  A,  the  glottis  during  the  emission  of  a  high  note  in  singing;  B,  in  easy  and  quiet  inhalation 
of  air;  C,  in  the  state  of  widest  possible  dilatation,  as  in  inhaling  a  very  deep  breath.  The  diagrams 
A',  B',  and  C,  show  in  horizontal  sections  of  the  glottis  the  position  of  the  vocal  ligaments  and 
arytenoid  cartilages  in  the  three  several  states  represented  in  the  other  figures.  In  alt  the  figures, 
so  far  as  marked,  the  letters  indicate  the  parts  as  follows,  viz.:  I,  the  base  of  the  tongue;  e,  the 
upper  free  part  of  the  epiglottis,  e',  the  tubercle  or  cushion  of  the  epiglottis;  ph,  part  of  the  ante- 
rior wall  of  the  pharynx  behind  the  larynx;  in  the  margin  of  the  aryteno-epiglottidean  fold  w,  the 
swelling  of  the  membrane  caused  by  the  cartilages  of  Wrisberg;  s,  that  of  the  cartilages  of  San- 
torini;  a,  the  tip  or  summit  of  the  arytenoid  cartilages;  c  v,  the  true  vocal  cords  or  lips  of  the  rima 
glottidis;  cv  s,  the  superior  or  false  vocal  cords;  between  them  tht,  ventricle  of  the  larynx;  in  C,  tr 
is  placed  on  the  anter.or  wall  of  the  receding  trachea,  and  b  indicates  the  commencement  of  the 
two  bronchi  beyond  the  bifurcation  which  may  be  brought  into  view  in  this  state  of  extreme  dilata- 
tion.   (Quain  after  Czermak.) 

lozenge-shaped.     At  the  moment  of  the  emission  of  sound,  it  is  narrowed, 
the  margins  of  the  arytenoid  cartilages  being  brought  into  contact  and 


THE    VOICE    AND    SPEECH.  .  443 

the  edges  of  the  vocal  cords  approximated  and  made  parallel,  at  the  same 
time  that  their  tension  is  much  increased.  The  higher  the  note  produced, 
the  tenser  do  the  cords  become  (Fig.  307,  a);  and  the  range  of  a  voice 
depends,  of  course,  in  the  main,  on  the  extent  to  which  the  degree  of 
tension  of  the  vocal  cords  can  be  thus  altered.  In  the  production  of  a 
high  note,  the  vocal  cords  are  brought  well  within  sight,  so  as  to  be 
plainly  visible  with  the  help  of  the  laryngoscope.  In  the  utterance  of 
grave  tones,  on  the  other  hand,  the  epiglottis  is  depressed  and  brought 
over  them,  and  the  arytenoid  cartilages  look  as  if  they  were  trying  to 
hide  themselves  under  it  (Fig.  308).  The  epiglottis,  by  being  somewhat 
pressed  down  so  as  to  cover  the  superior  cavity  of  the  larynx,  serves  to 
render  the  notes  deeper  in  tone,  and  at  the  same  time  somewhat  duller, 
just  as  covering  the  end  of  a  short  tube  placed  in  front  of  caoutchouc 
tongues  lowers  the  tone.  In  no  other  respect  does  the  epiglottis  appear 
to  have  any  effect  in  modifying  the  vocal  sounds. 

The  degree  of  approximation  of  the  vocal  cords  also  usually  corre- 
sponds with  the  height  of  the  note  produced;  but  probably  not  always,. 


Fig.  308.— View  of  the  upper  part  of  the  larynx  as  seen  by  means  of  the  laryngoscope  during 
the  utterance  of  a  grave  note,  c,  epiglottis;  s,  tubercles  of  the  cartilages  of  Santorini:  a,  arytenoid 
cartilages;  z,  base  of  the  tongue;  ph,  the  posterior  wall  of  the  pharynx.    (Czermak. ) 

for  the  width  of  the  aperture  has  no  essential  influence  on  the  height  of 
the  note,  as  long  as  the  vocal  cords  have  the  same  tension:  only  with  a 
wide  aperture,  the  tone  is  more  difficult  to  produce,  and  is  less  perfect, 
the  rushing  of  the  air  through  the  aperture  being  heard  at  the  same  time. 
No  true  vocal  sound  is  produced  at  the  posterior  part  of  the  aperture 
of  the  glottis,  that,  viz.,  which  is  formed  by  the  space  between  the  ary- 
tenoid cartilages.  For  if  the  arytenoid  cartilages  be  approximated  in 
such  a  manner  that  their  anterior  processes  touch  each  other,  but  yet 
leave  an  opening  behind  them  as  well  as  in  front,  no  second  vocal  tone  is 
produced  by  the  passage  of  the  air  through  the  posterior  opening,  but 
merely  a  rustling  or  bubbling  sound;  and  the  height  or  pitch  of  the  note 
produced  is  the  same  whether  the  posterior  part  of  the  glottis  be  open  or 
not,  provided  the  vocal  cords  maintain  the  same  degree  of  tension. 

The  Voice  in  Singing  and  Speaking. 

Varieties  of  Vocal   Sounds. — The  laryngeal   notes  may  observe 
three  different  kinds  of  sequence.      The  first  is  the  monotonous,  in  which 


444  HANDBOOK   OF   PHYSIOLOGY. 

the  notes  have  nearly  all  the  same  pitch  as  in  ordinary  speaking;  the 
variety  of  the  sounds  of  speech  being  due  to  articulation  in  the  mouth. 
In  speaking,  however,  occasional  syllables  generally  receive  a  higher  in- 
tonation for  the  sake  of  accent.  Tlie  second  mode  of  sequence  is  the  suc- 
cessive transition  from  high  to  low  notes,  and  vice  versa,  without  inter- 
vals; such  as  is  heard  in  the  sounds,  which,  as  expressions  of  passion, 
accompany  crying  in  men,  and  in  the  howling  and  whining  of  dogs. 
The  third  mode  of  sequence  of  the  vocal  sounds  is  the  musical,  in  which 
each  sound  has  a  determinate  number  of  vibrations,  and  the  numbers  of 
the  vibrations  in  the  successive  sounds  have  the  same  relative  proportions 
that  characterize  the  notes  of  the  musical  scale. 

In  different  individuals  this  comprehends  one,  two,  or  three  octaves. 
In  singers — that  is,  in  persons  apt  for  singing — it  extends  to  two  or  three 
octaves.  But  the  male  and  female  voices  commence  and  end  at  different 
points  of  the  musical  scale.  The  lowest  note  of  the  female  voice  is  about 
an  octave  higher  than  the  lowest  of  the  male  voice;  the  highest  note  of 
the  female  voice  about  an  octave  higher  than  the  highest  of  the  male. 
The  compass  of  the  male  and  female  voices  taken  together,  or  the  entire 
scale  of  the  human  voice,  includes  about  four  octaves.  The  principal 
difference  between  the  male  and  female  voice  is,  therefore,  in  their  pitch; 
but  they  are  also  distinguished  by  their  tone, — the  male  voice  is  not  so 
soft.  The  voice  presents  other  varieties  besides  that  of  male  and  female; 
there  are  two  kinds  of  male  voice,  technically  called  the  bass  and  tenor, 
and  two  kinds  of  female  voice,  the  contralto  and  soprano,  all  differing 
from  each  other  in  tone.  The  bass  voice  usually  reaches  lower  than 
the  tenor,  and  its  strength  lies  in  the  low  notes;  while  the  tenor 
voice  extends  higher  than  the  bass.  The  contralto  voice  has  generally 
lower  notes  than  the  soprano,  and  is  strongest  in  the  lower  notes  of  the 
female  voice;  while  the  soprano  voice  reaches  higher  in  the  scale.  But 
the  difference  of  compass,  and  of  power  in  different  parts  of  the  scale,  is 
not  the  essential  distinction  between  the  different  voices;  for  bass  singers 
can  sometimes  go  very  high,  and  the  contralto  frequently  sings  the  high 
notes  like  soprano  singers.  The  essential  difference  between  the  bass 
and  tenor  voices,  and  between  the  contralto  and  soprano,  consists  in 
their  tone  or  "  timbre/'  which  distinguishes  them  even  when  they  are 
singing  the  same  note.  The  qualities  of  the  barytone  and  mezzo-soprano 
voices  are  less  marked;  the  barytone  being  intermediate  between  the 
bass  and  tenor,  the  mezzo-soprano  between  the  contralto  and  soprano. 
They  have  also  a  middle  position  as  to  pitch  in  the  scale  of  the  male 
and  female  voices. 

The  different  pitch  of  the  male  and  the  female  voices  depends  on  the 
different  length  of  the  vocal  chords  in  the  two  sexes;  their  relative 
length  in  men  and  women  being  as  three  to  two.  The  difference  of  the 
two  voices  in  tone  or  "  timbre,"  is  owing  to  the  different  nature  and 


THE    VOICE    AND    SPEECH.  445 

form  of  the  resounding  walls,  which  in  the  male  larynx  are  much  more 
extensive,  and  form  a  more  acute  angle  anteriorly.  The  different  quali- 
ties of  the  tenor  and  bass,  and  of  the  alto  and  soprano  voices,  probably 
depend  on  some  peculiarities  of  the  ligaments,  and  the  membranous  and 
cartilaginous  varieties  of  the  laryngeal  cavity,  which  are  not  at  present 
understood,  but  of  which  we  may  form  some  idea,  by  recollecting  that 
musical  instruments  made  of  different  materials,  e.g.,  metallic  and  gut- 
strings,  may  be  tuned  to  the  same  note,  but  that  each  will  give  it  with  a 
peculiar  tone  of  "  timbre." 

The  larynx  of  boys  resembles  the  female  larynx;  their  vocal  cords 
before  puberty  are  not  two-thirds  the  length  of  the  adult  cords;  and  the 
angle  of  their  thyroid  cartilage  is  as  little  prominent  as  in  the  female 
larynx.  Boys'  voices  are  alto  and  soprano,  resembling  in  pitch  those  of 
women,  but  louder,  and  differing  somewhat  from  them  in  tone.  But, 
after  the  larynx  has  undergone  the  change  produced  during  the  period 
of  development  at  puberty,  the  boy's  voice  becomes  bass  or  tenor. 
While  the  change  of  form  is  taking  place,  the  voice  is  said  to  "crack;" 
it  becomes  imperfect,  frequently  hoarse  and  crowing,  and  is  unfitted  for 
singing  until  the  new  tones  are  brought  under  command  by  practice.  In 
eunuchs,  who  have  been  deprived  of  the  testes  before  puberty,  the  voice 
does  not  undergo  this  change.  The  voice  of  most  old  people  is  deficient 
in  tone,  unsteady,  and  more  restricted  in  extent:  the  first  defect  is  owing 
to  the  ossification  of  the  cartilages  of  the  larynx  and  the  altered  condi- 
tion of  the  vocal  cords;  the  want  of  steadiness  arises  from  the  loss  of 
nervous  power  and  command  over  the  muscles;  the  result  of  which  is 
here,  as  in  other  parts,  a  tremulous  movement.  These  two  causes 
combined  render  the  voices  of  old  people  void  of  tone,  unsteady,  bleat- 
ing, and  weak. 

In  any  class  of  persons  arranged,  as  in  an  orchestra,  according  to  the 
character  of  voices,  each  would  possess,  with  the  general  characteristics 
of  a  bass,  or  tenor,  oa'  any  other  kind  of  voice,  some  peculiar  character 
by  which  his  voice  would  be  recognized  from  all  the  rest.  The  condi- 
tions that  determine  these  distinctions  are,  however,  quite  unknown. 
They  are  probably  inherent  in  the  tissues  of  the  larynx,  and  are  as  in- 
discernible as  the  minute  differences  that  characterize  men's  features; 
one  often  observes,  in  like  manner,  hereditary  and  family  peculiarities  of 
voice,  as  well  marked  as  those  of  the  limbs  or  face. 

Most  persons,  particularly  men,  have  the  power,  if  at  all  capable  of 
singing,  of  modulating  their  voices  through  a  double  series  of  notes  of 
different  character:  namely,  the  notes  of  the  natural  voice,  or  chest- 
notes,  and  the  falsetto  notes.  The  natural  voice,  which  alone  has  been 
hitherto  considered,  is  fuller,  and  excites  a  distinct  sensation  of  much 
stronger  vibration  and  resonance  than  the  falsetto  voice,  which  has  more 
a  flute-like  character.     The  deeper  notes  of  the  male  voice  can  be  pro- 


446  HANDBOOK    OF    PHYSIOLOGY. 

duced  only  with  the  natural  voice,  the  highest  with  the  falsetto  only;  the 
notes  of  middle  pitch  can  be  produced  either  with  the  natural  or  falsetto 
voice;  the  two  registers  of  the  voice  are  therefore  not  limited  in  such  a 
manner  as  that  one  ends  when  the  other  begins,  but  they  run  in  part 
side  by  side. 

Method  of  the  Production  of  Notes. — The  natural  or  chest-notes, 
are  produced  by  the  ordinary  vibrations  of  the  vocal  cords.  The  mode 
of  production  of  the  falsetto  notes  is  still  obscure. 

By  Muller  the  falsetto  notes  were  thought  to  be  due  to  vibrations  of 
only  the  inner  borders  of  the  vocal  cords.  In  the  opinion  of  Petrequin 
and  Diday  they  do  not  result  from  vibrations  of  the  vocal  cords  at  all, 
but  from  vibrations  of  the  air  passing  through  the  aperture  of  the  glot- 
tis, which  they  believe  assumes,  at  such  times,  the  contour  of  the  em- 
bouchure of  a  flute.  Others  (considering  some  degree  of  similarity 
which  exists  between  the  falsetto  notes  and  the  peculiar  tones  called  har- 
monic, which  are  produced  when,  by  touching  or  stopping  a  harp-string 
at  a  particular  point,  only  a  portion  of  its  length  is  allowed  to  vibrate) 
have  supposed  that,  in  the  falsetto  notes,  portions  of  the  vocal  ligaments 
are  thus  isolated,  and  made  to  vibrate  while  the  rest  are  held  still.  The 
question  cannot  yet  be  settled;  but  any  one  in  the  habit  of  singing  may 
assure  himself,  both  by  the  difficulty  of  passing  smoothly  from  one  set 
of  notes  to  the  other,  and  by  the  necessity  of  exercising  himself  in  both 
registers,  lest  he  should  become  very  deficient  in  one,  that  there  must  be 
some  great  difference  in  the  modes  in  which  their  respective  notes  are 
produced. 

The  strength  of  the  voice  depends  partly  (a)  on  the  degree  to  which 
the  vocal  cords  can  be  made  to  vibrate;  and  partly  (i)  on  the  fitness  for 
resonance  of  the  membranes  and  cartilages  of  the  larynx,  of  the  pari- 
etes  of  the  thorax,  lungs,  and  cavities  of  the  mouth,  nostrils,  and  com- 
municating sinuses.  It  is  diminished  by  anything  which  interferes  with 
such  capability  of  vibration. 

The  intensity  or  loudness  of  a  given  note  with  maintenance  of  the 
same  "pitch,"  cannot  be  rendered  greater  by  merely  increasing  the  force 
of  the  current  of  air  through  the  glottis;  for  increase  of  the  force  of  the 
current  of  air,  cceteris  paribus,  raises  the  pitch  both  of  the  natural  and 
the  falsetto  notes.  Yet,  since  a  singer  possesses  the  power  of  increasing 
the  loundness  of  a  note  from  the  faintest  "piano"  to  "fortissimo" 
without  its  pitch  being  altered,  there  must  be  some  means  of  compen- 
sating the  tendency  of  the  vocal  cords  to  emit  a  higher  note  when  the 
force  of  the  current  of  air  is  increased.  This  means  evidently  consists 
in  modifying  the  tension  of  the  vocal  cords.  When  a  note  is  rendered 
louder  and  more  intense,  the  vocal  cords  must  be  relaxed  by  remission  of 
the  muscular  action,  in  proportion  as  the  force  of  the  current  of  the 
breath  through  the  glottis  is  increased.  When  a  note  is  rendered  fainter, 
the  reverse  of  this  must  occur. 


THE    VOICE    AND    SPEECH.  447 

The  arches  of  the  palate  and  the  uvula  become  contracted  during 
the  formation  of  the  higher  notes;  but  their  contraction  is  the  same  for 
a  note  of  given  height,  whether  it  be  falsetto  or  not;  and  in  either  case 
the  arches  of  the  palate  may  be  touched  with  the  finger,  without  the 
note  being  altered.  Their  action,  therefore,  in  the  production  of  the 
higher  notes  seems  to  be  merely  the  result  of  involuntary  associate  ner- 
vous action,  excited  by  the  voluntarily  increased  exertion  of  the  muscles 
of  the  larynx.  If  the  palatine  arches  contribute  at  all  to  the  production 
of  the  higher  notes  of  the  natural  voice  and  the  falsetto,  it  can  only  be 
by  their  increased  tension  strengthening  the  resonance. 

The  office  of  the  ventricles  of  the  larynx  is  evidently  to  afford  a  free 
space  for  the  vibrations  of  the  lips  of  the  glottis;  they  may  be  compared 
with  Jthe  cavity  at  the  commencement  of  the  mouth-piece  of  trumpets, 
which  allows  the  free  vibration  of  the  lips. 

Speech. — Besides  the  musical  tones  formed  in  the  larynx,  a  great 
number  of  other  sounds  can  be  produced  in  the  vocal  tubes,  between  the 
glottis  and  the  external  apertures  of  the  air-passages,  the  combination  of 
which  sounds  by  the  agency  of  the  cerebrum  into  different  groups  to 
designate  objects,  properties,  actions,  etc.,  constitutes  language.  The 
languages  do  not  employ  all  the  sounds  which  can  be  produced  in  this 
manner,  the  combination  of  some  with  others  being  often  difficult. 
Those  sounds  which  are  easy  of  combination  enter,  for  the  most  part, 
into  the  formation  of  the  greater  number  of  languages.  Each  language 
contains  a  certain  number  of  such  sounds,  but  in  no  one  are  all  brought 
together.  On  the  contrary,  different  languages  are  characterized  by  the 
prevalence  in  them  of  certain  classes  of  these  sounds,  while  others  are 
less  frequent  or  altogether  absent. 

Articulate  Sounds. — The  sounds  produced  in  speech,  or  the  ar- 
ticulate sounds,  are  commonly  divided  into  vowels  and  consonants,  the 
distinction  between  which  is,  that  the  sounds  for  the  former  are  gene- 
rated by  the  larynx,  while  those  of  the  latter  are  produced  by  interrup- 
tion of  the  current  of  air  in  some  part  of  the  air-passages  above  the 
larynx.  The  term  consonant  has  been  given  to  these  because  several  of 
them  are  not  properly  sounded,  except  consonantly  with  a  vowel.  Thus, 
if  it  be  attempted  to  pronounce  aloud  the  consonants  b,  d,  and  g,  or 
their  modifications,  p,  t,  k,  the  intonation  only  follows  them  in  their 
combination  with  a  vowel.  To  recognize  the  essential  properties  of  the 
articulate  sounds,  it  is  necessary  first  to  examine  them  as  they  are  pro- 
duced in  whispering,  and  then  investigate  which  of  them  can  also  be 
uttered  in  a  modified  character  conjoined  with  vocal  tone.  By  this  pro- 
cedure we  find  two  series  of  sounds:  in  one  the  sounds  are  mute,  and 
-cannot  be  uttered  with  a  vocal  tone;  the  sounds  of  the  other  series  can 
be  formed  independently  of  the  voice,  but  are  also  capable  of  being  ut- 
tered in  conjunction  with  it. 


448  HANDBOOK   OF    PHYSIOLOGY. 

All  the  vozvels  can  be  expressed  in  a  whisper  without  vocal  tone,  that 
is,  mutely.  These  mute  vowel-sounds  differ,  however,  in  some  measure, 
as  to  their  mode  of  production,  from  the  consonants.  All  the  mute 
consonants  are  formed  in  the  vocal  tube  above  the  glottis,  or  in  the 
cavity  of  the  mouth  or  nose,  by  the  mere  rushing  of  the  air  between  the 
surfaces  differently  modified  in  disposition.  But  the  sound  of  the 
vowels,  even  when  mute,  has  its  source  in  the  glottis,  though  its  vocal 
cords  are  not  thrown  into  the  vibrations  necessary  for  the  production  of 
voice;  and  the  sound  seems  to  be  produced  by  the  passage  of  the  current 
of  air  between  the  relaxed  vocal  cords.  The  same  vowel-sound  can  be 
produced  in  the  larynx  with  the  mouth  closed,  the  nostrils  being  open, 
and  the  utterance  of  all  vocal  tone  avoided.  The  sound,  when  the 
mouth  is  open,  is  so  modified  by  varied  forms  of  the  oral  cavity,  as  to 
assume  the  characters  of  the  vowels  a,  e,  i,  o,  u,  in  all  their  modifi- 
cations. 

The  cavity  of  the  mouth  assumes  the  same  form  for  the  articulation 
of  each  of  the  mute  vowels  as  for  the  corresponding  vowel  when  vocal- 
ized; the  only  difference  in  the  two  cases  lies  in  the  kind  of  sound 
emitted  by  the  larynx.  It  has  been  pointed  out  that  the  conditions 
necessary  for  changing  one  and  the  same  sound  into  the  different  vowels, 
are  differences  in  the  size  of  two  parts — the  oral  canal  and  the  oral  open- 
ing; and  the  same  is  the  case  with  regard  to  the  mute  vowels.  By  oral 
canal  is  meant  here  the  space  between  the  tongue  and  palate;  for  the 
pronunciation  of  certain  vowels  both  the  opening  of  the  mouth  and  the 
space  just  mentioned  are  widened;  for  the  pronunciation  of  other  vowels 
both  are  contracted;  and  for  others  one  is  wide,  the  other  contracted. 
Admitting  five  degrees  of  size,  both  of  the  opening  of  the  mouth  and  of 
the  space  between  the  tongue  and  palate,  Kempelen  thus  states  the 
dimensions  of  these  parts  for  the  following  vowel-sounds: 


Vowel.            Sound. 

Size  of  oral 

opening. 

Size  of  oral  canal. 

a    as  in  "  far  " 

5 

, 

3 

a         "    "  name  " 

4 

. 

2 

e         "    -''theme" 

3 

, 

1 

0         "    "go" 

2 

. 

4 

oo      "    "cool" 

1 

. 

5 

Another  important  distinction  in  articulate  sounds  is,  that  the  utter- 
ance of  some  is  only  of  momentary  duration,  taking  place  during  a  sud- 
den change  in  the  conformation  of  the  mouth,  and  being  incapable  of 
prolongation  by  a  continued  expiration.  To  this  class  belong  b,  p,  d, 
and  the  hard  g.  In  the  utterance  of  other  consonants  the  sounds  may 
be  continuous;  they  may  be  prolonged,  ad  libitum,  as  long  as  a  particu- 
lar disposition  of  the  mouth  and  a  constant  expiration  are  maintained. 
Among  these  consonants  are  h,  m,  n,  f,  s,  r,  1.     Corresponding  differ- 


THE    VOICE    AND    SPEECH.  449 

ences  in  respect  to  the  time  that  may  be  occupied  in  the  irutterance  ex- 
ist in  the  vowel  sounds,  and  principally  constitute  the  differences  of  long 
and  short  syllables.  Thus  the  a  as  in  "  far"  and  "fate,"  the  o  as  in 
"go"  and  "fort,"  may  be  indefinitely  prolonged;  but  the  same  vowels 
(or  more  properly  different  vowels  expressed  by  the  same  letters),  as  in 
"can"  and  "fact,"  in  "dog"  and  "  rotten,"  cannot  be  prolonged. 

All  sounds  of  the  first  or  explosive  kind  are  insusceptible  of  combina- 
tion with  vocal  tone  ("intonation"),  and  are  absolutely  mute;  nearly  all 
the  consonants  of  the  second  or  continuous  kind  may  be  attended  with 
"intonation." 

Ventriloquism. — The  peculiarity  of  speaking,  to  which  the  term 
ventriloquism  is  applied,  appears  to  consist  merely  in  the  varied  modifi- 
cation of  the  sounds  produced  in  the  larynx,  in  imitation  of  the  modifi- 
cations which  voice  ordinarily  suffers  from  distance,  etc.  From  the  ob- 
servations of  Miiller  and  Columbat,  it  seems  that  the  essential  mechanical 
parts  of  the  process  of  ventriloquism  consist  in  taking  a  full  inspiration, 
then  keeping  the  muscles  of  the  chest  and  neck  fixed,  and  speaking 
with  the  mouth  almost  closed,  and  the  lips  and  lower  jaw  as  motionless 
as  possible,  while  air  is  very  slowly  expired  through  a  very  narrow  glottis; 
care  being  taken  also,  that  none  of  the  expired  air  passes  through  the 
nose.  But,  as  observed  by  Miiller,  much  of  the  ventriloquist's  skill  in 
imitating  the  voices  coming  from  particular  directions,  consists  in  de- 
ceiving other  senses  than  hearing.  We  never  distinguish  very  readily 
the  direction  in  which  sounds  reach  our  ear;  and,  when  our  attention  is 
directed  to  a  particular  point,  our  imagination  is  very  apt  to  refer  to 
that  point  whatever  sounds  we  may  hear. 

Action  of  the  Tongue  in  Speech. — The  tongue,  which  is  usually 
credited  with  the  power  of  speech — language  and  speech  being  often 
employed  as  synonymous  terms — plays  only  a  subordinate,  although  very 
important  part.  This  is  well  shown  by  cases  in  which  nearly  the  whole 
organ  has  been  removed  on  account  of  disease.  Patients  who  recover 
from  this  operation  talk  imperfectly,  and  their  voice  is  considerably  modi- 
fied; but  the  loss  of  speech  is  confined  to  those  letters,  in  the  pronuncia- 
tion of  which  the  tongue  is  concerned. 

Stammering"  depends  on  a  want  of  harmony  between  the  action  of 
the  muscles  (chiefly  abdominal)  which  expel  air  through  the  larynx,  and 
that  of  the  muscles  which  guard  the  orifice  (rima  glottidis)  by  which  it 
escapes,  and  of  those  (of  tongue,  palate,  etc.)  which  modulate  the  sound 
to  the  form  of  speech. 

Over  either  of  the  groups  of  muscles,  by  itself,  a  stammerer  may  have 
as  much  power  as  other  people.     But  he  cannot  harmoniously  arrange 
their  conjoint  actions. 
29 


CHAPTER    XVII. 

THE  NERVOUS  SYSTEM. 

I.  The  Structure  of  the  Nervous  Elements. 

Nervous  tissue  is  found  under  the  microscope  to  consist  essentially 
of  two  main  elements,  namely,  of  nerve  fibres  and  nerve  cells.  When  the 
nerve  fibres  are  collected  together  into  bundles  they  form  nerve  trunks  or 
nerves.  When  nerve  cells  are  collected  together  they  form  nerve  ganglia, 
but  in  such  ganglia  nerve-fibres  are  also  invariably  found. 

A.  Nerve  Fibres. 

Varieties. — In  most  nerve-trunks  two  kinds  of  fibres  are  mingled, 
called  (a)  medullated  or  white  fibres,  and  (b)  non-medullated  or  gray 
fibres. 

(a.)  Medullated  Fibres. — Each  medullated  nerve-fibre  is  made  up 
of  the  following  parts: — (1.)  An  external  sheath  called  the  primitive 
nerve  sheath,  or  nucleated  sheath  of  Schwann;  (2.)  An  intermediate  or 
packing  substance  known  as  the  medullary  sheath,  or  white  substance  of 
Schwann;  and  (3.)  internally  the  axis-cylinder,  primitive  band,  axis 
band,  or  axial  fibre. 

Although  these  parts  can  be  made  out  in  nerves  examined  some  time 
after  death,  in  a  recent  specimen  the  contents  of  the  nerve-sheath  appear 
to  be  homogeneous.  But  by  degrees  they  undergo  changes  which  show 
them  to  be  composed  of  two  different  materials.  The  internal  or  cen- 
tral part,  occupying  the  axis  of  the  tube  {axis-cylinder),  becomes  gray- 
ish, while  the  outer,  or  cortical  portion  {white  substance  of  Schwann), 
becomes  opaque  and  dimly  granular  or  grumous,  as  if  from  a  kind  of 
coagulation.  At  the  same  time,  the  fine  outline  of  the  previously  trans- 
parent cylindrical  tube  is  exchanged  for  a  dark  double  contour  (Fig.  309, 
b),  the  outer  line  being  formed  by  the  sheath  of  the  fibre,  the  inner  by 
the  margin  of  curdled  or  coagulated  medullary  substance.  The  granu- 
lar material  shortly  collects  into  little  masses,  which  distend  portions  of 
the  tubular  membrane;  while  the  intermediate  spaces  collapse,  giving 
the  fibres  a  varicose,  or  beaded  appearance  (Fig.  309,  c  and  d),  instead 
of  the  previous  cylindrical  form.     The  whole  contents  of  the  nerve- 


THE    NERVOUS    SYS'lEM. 


45: 


tubules  are  extremely  soft,  for  when  subjected  to  pressure  they  readily 
pass  from  one  part  of  the  tubular  sheath  to  another,  and  often  cause  a 
bulging  at  the  side  of  the  membrane.  They  also  readily  escape,  on 
pressure,  from  the  extremities  of  the  tubule,  in  the  form  of  a  grumous 
or  granular  material. 

(1.)  The  external  nucleated  sheath  of  Schwann  is  a  pellucid  mem- 
brane, forming  the  outer  investment  of  the  nerve-fibre.  Within  this 
delicate  structureless  membrane  nuclei  are  seen  at  intervals,  surrounded 
by  a  variable  amount  of  protoplasm.  The  sheath  is  structureless,  like 
the  sarcolemma,  and  the  nuclei  appear  to  be  within  it:  together  with 
the  protoplasm  which  surrounds  them,  they  are  the  relics  of  embryonic 


Fig.  309. 


Fig.  310. 


Fig. 


Fig.  309. — Primitive  nerve-fibres,  a.  A  perfectly  fresh  tubule  with  a  single  dark  outline,  b.  A 
tubule  or  fibre  with  a  double  contour  from  commencing  post-mortem  change,  c.  The  changes 
further  advanced,  producing  a  varicose  or  beaded  appearance,  d.  A  tubule  or  fibre,  the  central 
part  of  which,  in  consequence  of  still  further  changes,  has  accumulated  in  separate  portions  within 
the  sheath.    (Wagner. ) 

Fig.  310.— Two  nerve-fibres  of  sciatic  nerve,  a.  Node  of  Ranvier.  b.  Axis-cylinder,  c.  Sheath 
of  Schwann,  with  nuclei.     X  300.    (Klein  and  Noble  Smith.) 

Fig.  311.— A  node  of  Ranvier  in  a  medullated  nerve  fibre,  viewed  from  above.  The  medullary 
sheath  is  interrupted,  and  the  primitive  sheath  thickened.  Copied  from  Axel  Key  and  Retzius. 
X  750.    cKlein  and  Noble  Smith.) 


cells,  and  from  their  resemblance  to  the  muscle  corpuscles  of  striated 
muscle,  may  be  termed  nerve-corpuscles.  They  are  easily  stained  with 
logwood  and  other  dyes. 

(2.)  The  medullary  sheath  or  white  substance  of  Schwann  is  the  part 
to  which  the  peculiar  white  aspect  of  some  nerves  is  principally  due.  It 
is  a  thick,  fatty,  semi-fluid  substance,  as  we  have  seen,  possessing  a 
double  contour.     It  is  said  to  be  made  up  of  a  fine  reticulum  (Stilling, 


452  HANDBOOK    OF    PHYSIOLOGY. 

Klein),  in  the  meshes  of  which  is  imbedded  the  bright  fatty  material. 
It  stains  well  with  osmic  acid. 

According  to  McCarthy,  the  medullary  sheath  is  composed  of  small 
rods  radiating  from  the  axis-cylinder  to  the  sheath  of  Schwann.  Some- 
times the  whole  space  is  occupied  by  them,  whilst  at  other  times  the 
rods  appear  shortened,  and  compressed  laterally  into  bundles  imbedded 
in  some  homogeneous  substance. 

(3. )  The  axis-cylinder  consists  of  a  large  number  of  primitive  fibrillar. 
This  is  well  shown  in  the  corneas,  where  the  axis-cylinders  of  nerves 
break  up  into  minute  fibrils  which  go  to  form  terminal  networks,  and 
also  in  the  spinal  cord,  where  these  fibrillae  form  a  large  part  of  the  gray 
matter.  From  various  considerations,  such  as  its  invariable  presence 
and  unbroken  continuity  in  all  nerves,  though  the  primitive  sheath  or 
the  medullary  sheath  may  be  absent,  there  can  be  little  doubt  that  the 
axis  cylinder  is  the  essential  part  of  the  fibre,  the  other  parts  having  the 
subsidiary  function  of  support  and  possibly  of  insulation. 

At  regular  intervals  in  most  medullated  nerves,  the  nucleated  sheath 
of  Schwann  possesses  annular  constrictions  (nodes  of  Ranvier).  At  these 
points  (Figs.  310,  311),  the  continuity  of  the  medullary  white  substance 
is  interrupted,  and  the  primitive  sheath  comes  into  immediate  contact 
with  the  axis-cylinder. 

Size. — The  size  of  the  nerve-fibres  varies;  it  is  said  that  the  same 
fibres  may  not  preserve  the  same  diameter  through  their  whole  length. 
The  largest  fibres  are  found  within  the  trunks  and  branches  of  the 
spinal  nerves,  in  Avhich  the  majority  measure  from  14.4// *  to  19/*  in 
diameter.  In  the  so-called  visceral  nerves  of  the  brain  and  spinal  cord 
medullated  nerves  are  found,  the  diameter  of  which  varies  from  1.8//  to 
3.6/*.  In  the  hypoglossal  nerve  they  are  intermediate  in  size,  and  gen- 
erally measure  7.2//  to  10.8//. 

(b.)  Non-medullated  Fibres. — The  fibres  of  the  second  kind  (Fig. 
312),  which  constitute  the  whole  of  the  branches  of  the  olfactory  and 
auditory  nerves,  the  principal  part  of  the  trunk  and  branches  of  the 
sympathetic  nerves,  and  are  mingled  in  various  proportions  in  the  cere- 
brospinal nerves,  differ  from  the  preceding,  chiefly  in  their  fineness, 
being  only  about  %  to  £  as  large  in  their  course  within  the  trunks  and 
branches  of  the  nerves;  in  the  absence  of  the  double  contour;  in  their 
contents  being  apparently  uniform;  and  in  their  having,  when  in  bun- 
dles, a  yellowish-gray  hue  instead  of  the  whiteness  of  the  cerebro-spinal 
nerves.  These  peculiarities  depend  on  their  not  possessing  the  outer  layer 
of  medullary  substance;  their  contents  being  composed  exclusively  of 
the  axis-cylinder.  Yet,  since  many  nerve-fibres  may  be  found  which 
appear  intermediate  in  character  between  these  two  kinds,  and  since  the 


'  u  =  .001  mm. 


THE    NhKVoL'S    SYSTEM. 


458 


large  fibres,  as  they  approach  both  their  central  and  their  peripheral 
end,  lose  their  medullary  sheath,  and  assume  many  of  the  other  char- 
acters of  the  fine  fibres  of  the  sympathetic  system,  it  is  not  necessary  to 
suppose  that  there  is  any  material  difference  in  the  two  kinds  of  fibres. 


Fig.  312.— Gray,  pale,  or  gelatinous  nerve-fibres.  A.  From  a  branch  of  the  olfactory  nerve  of 
the  sheep:  a,  a,  two  dark-bordered  or  white  fibres  from  the  fifth  pair,  associated  with  the  pale 
olfactory  fibres.    B.  From  the  sympathetic  nerve.    X  450.    (Max  Schultze.) 

It  is  worthy  of  note,  that  in  the  foetus,  at  an  early  period  of  develop- 
ment, all  nerve-fibres  are  non-medullated. 

Nerve-trunks. — Each  nerve-trunk  is  composed  of  a  variable  number 
of  different-sized  bundles  {funiculi)  of  nerve-fibres  which  have  a  special 


Fig.  313.— Transverse  section  of  the  sciatic  nerve  of  a  cat  about  x  100.—  It  consists  of  bundles 
(Funiculi)  of  nerve-fibres  ensheathed  in  afihrous  supporting  capsule,  epineurium.  A;  each  bundle 
has  a  special  sheath  (not  sufficiently  marked  out  from  the  epineurium  in  the  figure)  or  perineurium 
B;  the  nerve-fibres  N / are  separated  from  one  another  by  endoneurium;  L,  lymph  spaces;  Ar. 
artery;  V,  vein;  F,  fat.    Somewhat  diagrammatic.    (V.  D.  Han-is.) 


sheath  (perineurium  or  neurilemma).     The  funiculi  are  inclosed  in  ;i 
firm  fibrous  sheath  (epineurium);  this  sheath  also  sends  in  processes  of 


45± 


HANDBOOK    OF  PHYSIOLOGY. 


connective  tissue  which  connect  the  bundles  togother.     In  the  funiculi 
between  the  fibres  is  a  delicate  supporting  tissue  (the  endoneurium). 

There  are  numerous  lymph-spaces  both  beneath  the  connective  tissue 
investing  individual  nerve-fibres,  and  also  beneath  that  which  surrounds 
the  funiculi. 


Fig.  314.— Several  fibres  of  a  bundle  of  medullated  nerve-fibres  acted  upon  by  silver  nitrate  to 
show  peculiar  behavior  of  nodes  of  Ranvier,  N,  towards  this  reagent.  The  silver  has  penetrated  at 
the  nodes,  and  has  stained  the  axis-cylinder,  Bt,  for  a  short  distance.  S,  the  white  substance. 
(Klein  and  Noble  Smith.) 

Course. — Everv  nerve-fibre  in  its  course  proceeds  uninterrupedly  from 
its  origin  in  a  nerve-centre  to  near  its  destination,  whether  this  be  the 


Fig.  315.— Small  branch  of  a  muscular  nerve  of  the  frog,  near  its  termination,  showing  divisions 
of  the  fibres,    a,  into  two;  b,  into  three.     X  350.    (Kolliker.) 

periphery  of  the  body,  another  nervous    centre,   or  the    same  centre 
whence  it  issued. 


THE   NERVOUS    SYSTEM.  455 

Bundles  of  fibres  run  together  in  the  nerve-trunk,  but  merely  lie  in 
apposition  with  each  other;  they  do  not  unite:  even  when  they  anasto- 
mose, there  is  no  union  of  fibres,  but  only  an  interchange  of  fibres  be- 
tween the  anastomosing  funiculi.  Although  each  nerve-fibre  is  thus 
single  and  undivided  through  nearly  its  whole  course,  yet  as  it  approaches 
the  region  in  which  it  terminates,  individual  fibres  break  up  into  several 
subdivions  (Fig.  315)  before  their  final  ending. 

Plexuses. — At  certain  parts  of  their  course,  nerves  form  plexuses ,  in 
which  they  anastomose  with  each  other,  as  in  the  case  of  the  brachial 
and  lumbar  plexuses.  The  objects  of  such  interchange  of  fibres  are,  (a) 
to  give  to  each  nerve  passing  off  from  the  plexus,  a  wider  connection 
with  the  spinal  cord  than  it  would  have  if  it  proceeded  to  its  destination 
without  such  communication  with  other  nerves.  Thus,  each  nerve  by 
the  wideness  of  its  connections,  is  less  dependent  on  the  integrity  of 
any  single  portion,  whether  of  nerve-centre  or  of  nerve-trunk,  from 
which  it  may  spring,  (b)  Each  part  supplied  from  a  plexus  has  wider 
relations  with  the  nerve-centres,  and  more  extensive  sympathies;  and,  by 
means  of  the  same  arrangement,  groups  of  muscles  may  be  co-ordinated, 
every  member  of  the  group  receiving  motor  filaments  from  the  same 
parts  of  the  nerve-centre,  (c)  Auy  given  part,  say  a  limb,  is  less  depen- 
dent upon  the  integrity  of  any  one  nerve. 

Nerve  terminations. — As  medullated  nerve-fibres  approach  their  ter- 
minations they  lose  their  medullary  sheath,  and  consist  then  merely  of 
axis-cylinder  and  primitive  sheath.  They  then  lose  also  the  latter,  and 
only  the  axis-cylinder  is  left  with  here  and  there  a  nerve-corpuscle  partly 
rolled  around  it.  Finally,  even  this  investment  ceases,  and  the  axis- 
cylinder  breaks  up  into  its  elementary  fibrillse. 

B.  Nerve-Cells  or  Corpuscles. 

Nerve-cells  comprise  the  second  principal  element  of  nervous  tissue. 
They  are  not  generally  present  in  nerve-trunks,  but  are  found  in  all  col- 
lections of  nervous  tissue  called  ganglia.  They  vary  considerably  in 
shape,  size,  and  structure  in  different  ganglia. 

a.  Some  of  them  are  small,  generally  spherical  or  ovoid,  and  have  a 
regular  uninterrupted  outline.  These  simple  nerve-cells  are  most  nume- 
rous in  the  sympathetic  ganglia;  each  is  inclosed  in  a  nucleated  sheath. 
b.  Others,  which  are  called  caudate  or  stellate  nerve-cells  (Fig.  317),  are 
larger,  and  have  one,  two,  or  more  long  processes  issuing  from  them,  the 
cells  being  called  respectively  unipolar,  bipolar,  or  multipolar:  which 
processes  often  divide  and  subdivide,  and  appear  tubular,  and  filled  with 
the  same  kind  of  granular  material  that  is  contained  within  the  cell. 
Of  these  processes  some  appear  to  taper  to  a  point  and  terminate  at  a 
greater  or  less  distance  from  the  cell;  some  appear  to  anastomose  with 
similar  offsets  from  other  cells;  while  others  are  continuous  with  nerve- 


456 


HANDBOOK    OF    PHYSIOLOGY. 


fibres,  the  prolongation  from  the  cell  by  degrees  assuming  the  character 
of  the  nerve-fibre  with  which  it  is  continuous. 

Ganglion-cells  are  generally  inclosed  in  a  transparent  membranous 
capsule  similar  in  appearance  to  the  nucleated  sheath  of  Schwann  in 
nerve-fibres:  within  this  capsule  is  a  layer  of  small  flattened  cells. 

That  process  of  a  nerve-cell  which  becomes  continuous  with  a  nerve- 
fibre  is  always  unbranched  as  it  leaves  the  cell.  It  at  first  has  all  the 
characters  of  an  axis-cylinder,  but  soon  acquires  a  medullary  sheath,  and 
then  may  be  termed  a  nerve-fibre.  This  continuity  of  nerve-cells  and 
fibres  may  be  readily  traced  out  in  the  anterior  cornua  of  the  gray  matter 
of  the  spinal  cord.  In  many  large  branched  nerve-cells  a  distinctly 
fibrillated  appearance  is  observable;  the  fibrillar  are  probably  continuous 
with  those  of  the  axis-cylinder  of  a  nerve. 


Fig.  316. 


Fig.  317. 


Fig.  316.— Ganglion  nerve-corpuscles  of  different  shapes.    (Klein  and  Noble  Smith. ) 
Fig.  317.— An  isolated  sympathetic  ganglion  cell  of  man,  showing  sheath  with  nucleated-cell  lin- 
ing, B.    A.  Ganglion-cell,  with  nucleus  and  nucleolus.    C.  Branched  process.    D.  Unbranched  pro- 
cess.    (Key  and  Retzius.)    X  750. 

Any  other  points  in  the  structure  of  nerve-cells  will  be  mentioned 
under  the  account  of  the  different  ganglia. 

II.  Function  of  Nerve-Fibres. 

From  the  account  of  nervous  action  previously  given  it  will  be  readily 
understood  (p.  428),  that  nerve-fibres  are  stimulated  to  act  by  anything 


THE    NERVOUS    SYSTEM.  457 

which,  with  sufficient  suddenness,  increases  their  irritability,  but  they 
are  incapable  of  originating  of  themselves  the  condition  necessary  for 
the  manifestation  of  their  own  energy.  The  stimulus  produces  its  effect 
upon  the  termination  of  the  nerve  stimulated,  being  conducted  to  it  by 
the  nerve-fibre.  The  effect  of  the  stimulus  upon  a  nerve  therefore  de- 
pends upon  the  nature  of  its  end-organ.  A  length  of  a  nerve-trunk 
when  freshly  removed  from  the  body,  if  stimulated  midway  between  its 
extremities,  will,  as  shown  by  the  deflection  of  a  needle  of  the  galvano- 
meter at  either  end,  conduct  the  electrical  impressions  in  either  direction, 
and  it  may  be  considered  therefore  only  an  accidental  circumstance  as  it 
were,  whether  when  in  situ  it  has  conducted  impressions  to  the  central 
nervous  system  from  the  periphery,  or  from  the  central  nervous  system 
to  the  muscles  or  other  tissues.  The  same  fibre  cannot  be  used  for  the 
one  purpose  at  one  time,  and  for  the  other  at  another,  simply  because  of 
the  nature  of  its  terminal  organs.  Thus,  when  a  cerebro-spinal  nerve- 
fibre  is  irritated  in  the  living  body  as  by  pinching,  or  by  heat,  or  by 
electrifying  it,  there  is,  under  ordinary  circumstauces,  one  of  two  effects 
— either  there  is  pain,  or  there  is  twitching  of  one  or  more  muscles  to 
which  the  nerve  distributes  its  fibres.  From  various  considerations  it  is 
certain  that  pain  is  always  the  result  of  a  change  in  the  nerve-cells  of 
the  brain.  Therefore,  in  such  an  experiment  as  that  referred  to,  the  ir- 
ritation of  the  nerve-fibre  is  conducted  in  one  of  two  directions,  i.  e., 
either  to  the  brain,  which  is  the  central  termination  of  the  fibre,  when 
there  is  pain,  or  to  a  muscle,  which  is  the  peripheral  termination,  when 
there  is  movement. 

That  this  is  the  true  explanation  is  made  highly  probable,  not  merely 
by  the  absence  of  any  essential  structural  differences  in  the  two  kinds 
of  nerve  fibre,  but  also  by  the  fact,  proved  by  direct  experiment,  that  if 
a  centripetal  nerve  (gustatory)  be  divided,  and  its  central  portion  be 
made  to  unite  with  the  distal  portion  of  a  divided  motor  nerve  (hypo- 
glossal) the  effect  of  irritating  the  former  after  the  parts  have  healed,  is 
to  excite  contraction  in  the  muscles  supplied  by  the  latter.  (Phillippeaux 
and  Vulpian.) 

The  effect  of  this  simple  experiment  is  a  type  of  what  always  occurs 
when  nerve-fibres  are  engaged  in  the  performance  of  their  functions. 
The  result  of  stimulating  them,  which  roughly  imitates  what  happens 
naturally  in  the  body,  is  found  to  occur  at  one  or  other  of  their  extremi- 
ties, central  or  peripheral,  never  at  both;  and  in  accordance  with  this 
fact,  and  because,  for  any  given  nerve-fibre,  the  result  is  always  the  same, 
nerves  are  commonly  classed  as  sensory  or  motor. 

Classification. — The  classification  of  nerve-fibres  into  sensory  and 
motor  is  not  altogether  accurate,  and  the  terms  Centripetal  or  afferent, 
and  Centrifugal  or  efferent  are  more  properly  used  in  connection  with 
nerve-fibres  in  lieu  of  the  corresponding  terms,  because  the  result  of 


458  HANDBOOK    OF    PHYSIOLOGY. 

stimulating  a  nerve  of  the  former  kind  is  not  always  the  production  of 
pain  or  other  form  of  sensation,  nor  is  motion  the  invariable  result  of 
stimulating  the  latter. 

The  term  intercentral  is  applied  to  those  nerve-fibreswhich  connect 
more  or  less  distinct  nerve-centres,  and  may,  therefore,  be  said  to  have 
no  peripheral  distribution,  in  the  ordinary  sense  of  the  term.  Nerve- 
fibres  then  are  either  (a)  Centripetal  or  afferent,  (b)  Centrifugal  or 
efferent,  or  (c)  Intercentral. 

Conduction  in  centripetal  nerves  may  cause  (a)  pain,  or  some  other 
kind  of  sensation;  (b)  special  sensation;  or  (c)  reflex  action  of  some  kind;, 
or  (d)  inhibition,  or  restraint  of  action. 

Conduction  in  centrifugal  nerves  may  cause  (a)  contraction  of  muscle 
(motor  nerves)  ;  (b)  it  may  influence  nutrition  (trophic  nerves)  ;  or  (c) 
may  influence  secretion  (secretory  nerves);  or  (d)  inhibit,  augment,  or 
stop  any  other  efferent  action. 

It  is  a  law  of  action  in  all  nerve-fibres,  and  corresponds  with  the  con- 
tinuity and  simplicity  of  their  course,  that  an  impression  made  on  any 
fibre,  is  simply  and  uninterruptedly  transmitted  along  it,  without  being 
imparted  or  diffused  to  any  of  the  fibres  lying  near  it.  In  other  words, 
all  nerve-fibres  are  mere  conductors  of  impressions.  Their  adaptation  to 
this  purpose  is,  perhaps,  due  to  the  contents  of  each  fibre  being  com- 
pletely isolated  from  those  of  adjacent  fibres  by  the  membrane  or  sheath 
in  which  each  is  inclosed,  and  which  acts,  it  may  be  supposed,  just  as 
silk,  or  other  non-conductors  of  electricity  do,  which,  when  covering  a 
wire,  prevent  the  electric  condition  of  the  wire  from  being  conducted 
into  the  surrounding  medium. 

Velocity  of  Nerve-force. — The  change  which  a  stimulus  sets  up  in  a 
nerve,  of  the  exact  nature  of  which  we  are  unacquainted,  appears  to 
travel  along  a  nerve-fibre  in  both  directions  in  the  form  of  a  wave  with 
considerable  velocity.  Helmholtz  and  Baxt  have  estimated  the  average 
rate  of  conduction  in  human  motor  nerves  at  111  feet  (nearly  29  metres) 
per  second;  this  result  agreeing  very  closely  with  that  previously  ob- 
tained. It  is  probably  rather  under  than  over  the  average  velocity. 
Rutherford's  observations  agree  with  those  of  Von  Wittich,  that  the 
rate  of  transmission  in  sensory  nerves  is  about  140  feet  per  second. 
Various  conditions  modify  the  rate  of  transmission,  of  which  temperature 
is  one  of  the  most  important,  a  very  low  or  a  very  high  temperature 
diminishing  it;  fatigue  of  the  nerve  acting  in  the  same  direction,  but 
increase  of  the  stimulus  up  to  a  certain  point  increasing  it,  as  does  also 
the  hathelectro tonic  condition  of  the  nerve. 

Conduction  in  Sensory  Nerves. — Centripetal  nerves  appear  able  to 
convey  impressions  only  from  the  parts  in  which  they  are  distributed, 
towards  the  nerve-centre  from  which  they  arise,  or  to  which  they  tend. 
Thus,  when  a  sensitive  nerve  is  divided,  and  irritation  is  applied  to  the 


THE    NERVOUS    SYSTEM. 


45£ 


end  of  the  proximal  portion,  i.  e.,  of  the  portion  still  connected  with 
the  nervous  centre,  sensation  is  perceived,  or  a  reflex  action  ensues;  but 
when  the  end  of  the  distal  portion  of  the  divided  nerve  is  irritated,  no 
effect  appears.  When  an  impression  is  made  upon  any  part  of  the  course 
of  a  sensory  nerve,  the  mind  may  perceive  it  as  if  it  were  made  not  only 
upon  the  point  to  which  the  stimulus  is  applied,  but  also  upon  all  the 
points  in  which  the  fibres  of  the  irritated  nerve  are  distributed:  in  other 
words,  the  effect  is  the  same  as  if  the  irritation  were  applied  to  the  parts 
supplied  by  the  branches  of  the  nerve.  When  the  whole  trunk  of  the 
nerve  is  irritated,  the  sensation  is  felt  at  all  parts  which  receive  branches 
from  it;  but  when  only  individual  portions  of  the  trunk  are  irritated, 
the  sensation  is  perceived  at  those  parts  only  which  are  supplied  by  the 
several  portions.  Thus,  if  we  compress  the  ulnar  nerve  where  it  lies  at 
the  inner  side  of  the  elbow  joint,  behind  the  internal  condyle,  we  have 
the  sensation  of  "pins  and  needles,"  or  of  a  shock,  in  the  parts  to  which 
its  fibres  are  distributed,  namely,  in  the  palm  and  back  of  the  hand, 
and  in  the  fifth  and  ulna  half  of  the  fourth  finger.  When  stronger 
pressure  is  made,  the  sensations  are  felt  in  the  fore-arm  also;  and  if  the 
mode  and  direction  of  the  pressure  be  varied,  the  sensation  is  felt  by 
turns  in  the  fourth  finger,  in  the  fifth,  and  in  the  palm  of  the  hand,  or 
in  the  back  of  the  hand,  according  as  different  fibres  or  fasciculi  of  fibres 
are  more  pressed  upon  than  others. 

Illustrations. — It  is  in  accordance  with  this  law,  that  when  parts  are 
deprived  of  sensibility  by  compression  or  division  of  the  nerves  supply- 
ing them,  irritation  of  the  portion  of  the  nerve  connected  with  the  brain 
still  excites  sensations  which  are  felt  as  if  derived  from  the  parts  to  which 
the  peripheral  extremities  of  the  nerve-fibres  are  distributed.  Thus, 
there  are  cases  of  paralysis  in  which  the  limbs  are  totally  insensible  to 
external  stimuli,  yet  are  the  seat  of  most  violent  pain,  resulting  appar- 
ently from  irritation  of  the  sound  part  of  the  trunk  of  the  nerve  still  in 
connection  with  the  brain,  or  from  irritation  of  those  parts  of  the  ner- 
vous centre  from  which  the  sensory  nerve  or  nerves  which  supply  the 
paralyzed  limbs  origiuate.  An  illustration  of  the  same  law  is  also  afforded 
by  the  cases  in  which  division  of  a  nerve  for  the  cure  of  neuralgic  pain 
is  found  useless,  and  in  which  the  pain  continues  or  returns,  though 
portions  of  the  nerves  are  removed.  In  such  cases,  the  disease  is  probably 
seated  nearer  the  nervous  centre  than  the  part  at  which  the  division  of 
the  nerve  is  made,  or  it  may  be  in  the  nervous  centre  itself.  In  the  same 
way  may  be  explained  the  fact,  than  when  part  of  a  limb  has  been  re- 
moved by  amputation,  the  remaining  portions  of  the  nerves  may  give  rise 
to  sensations  which  the  mind  refers  to  the  lost  part.  When  the  stump 
is  healed,  the  sensations  which  weave  accustomed  to  have  in  a  sound  limb 
are  still  felt;  and  tingling  and  pains  are  referred  to  the  parts  that  are 
lost,  or  to  particular  portions  of  them,  as  to  single  toes,  to  the  sole  of  the 
foot,  to  the  dorsum  of  the  foot,  etc. 

It  must  not  be  assumed,  as  it  often  has  been,  that  the  mind  has  no 
power  of  discriminating  the  very  point  in  the  length  of  any  nerve- 
fibre  to  which  an  irritation  is  applied.  Even  in  the  instances  referred 
to,  the  mind  perceives  the  pressure  of  a  nerve  at  the  point  of  pressure, 
as  well  as  in  the  seeming  sensations  derived  from  the  extremities  of  the 
fibres:  and  in  stumps,  pain  is  felt  in  the  stump,  as  well  as,  seemingly, 
in  the  parts  removed.  It  is  not  quite  certain  whether  these  sensations 
are    due  to  conduction    through    the  nerve-fibres  whic'i   are  on    their 


4:60  HANDBOOK   OF   PHYSIOLOGY. 

way  to  be  distributed  elsewhere,  or  through  the  sentient  extremities 
of  nerves  which  are  themselves  distributed  to  the  many  trunks  of 
the  nerves,  the  nervi  nervorum.  The  latter  is  the  more  probable  sup- 
position. 

Conduction  in  the  Nerves  of  Special  Sense. — The  laws  of  conduction 
in  the  olfactory,  optic,  auditory,  gustatory,  resemble  in  many  respects 
"those  of  conduction  in  the  nerves  of  common  sensation,  just  described. 
Thus  the  effect  is  always  central;  stimulation  of  the  trunk  of  the  nerve 
produces  the  same  effect  as  that  of  its  extremities,  and  if  the  nerve  be 
severed,  it  is  the  central  and  not  the  peripheral  extremity  which  re- 
sponds to  irritation,  although  the  sensation  is  referred  to  the  periphery. 
There  are,  however,  certain  peculiarities  in  the  effects.  Thus  the  various 
stimuli,  which  might  cause,  through  an  ordinary  sensitive  nerve,  the 
sense  of  pain,  would,  if  applied  to  the  optic  nerve,  cause  a  sensation  as  of 
flashes  of  light;  if  applied  to  the  olfactory,  there  would  be  a  sense  as  of 
something  smelt.     And  so  with  the  other  two. 

Hence  the  explanation  of  so-called  subjective  sensations.  Irritation 
in  the  optic  nerve,  or  the  part  of  the  brain  from  which  it  arises,  may  cause 
a  patient  to  believe  he  sees  flashes  of  light,  and  among  the  commonest 
troubles  of  the  nerves  of  special  sense,  is  the  distressing  noise  in  the 
head  {tinnitus  aurium),  which  depends  on  some  unknown  stimula- 
tion of  the  auditory  nerve  or  centre  quite  unconnected  with  external 
sounds. 

Conduction  in  Motor  Nerves. — Conduction  in  motor  nerves  presents 
a  remarkable  contrast  with  the  foregoing.  Thus,  the  effect  of  applying 
a  stimulus  to  the  motor  nerve  is  always  noticeable,  at  the  peripheral  ex- 
tremity, in  the  contraction  of  muscles  supplied  by  it.  If  a  motor  nerve 
be  severed,  irritation  of  the  distal  portion  causes  contraction  of  muscle, 
but  no  effect  whatever  is  produced  by  stimulating  that  part  of  the  nerve 
which  is  still  in  direct  connection  with  the  nerve-centre. 

Contractions  are  excited  in  all  the  muscles  supplied  by  the  branches 
given  off  by  the  nerve  below  the  point  irritated,  and  in  those  muscles 
alone:  the  muscles  supplied  by  the  branches  which  come  off  from  the 
nerve  at  a  higher  point  than  that  irritated,  are  not  directly  excited  to 
contraction.  And  it  is  from  the  same  fact  that,  when  a  motor  nerve 
enters  a  plexus  and  contributes  with  other  nerves  to  the  formation  of  a 
nervous  trunk  proceeding  from  the  plexus,  it  does  not  impart  motor 
power  to  the  whole  of  that  trunk,  but  only  retains  it  isolated  in  the  fibres 
which  form  its  continuation  in  the  branches  of  that  trunk. 

Nerve  Terminations. 

A.  Of  Sensory  Nerves. — (1.)  Pacinian  Corpuscles. — The  Pacinian 
bodies  or  corpuscles  (Figs.  318  and  319),  named  after  their  discoverer 
Pacini,  also  called  Corpuscles  of  Vater,  are  little  elongated  oval  bodies, 
situated  on  some  of  the  cerebro-spinal  and  sympathetic  nerves,  especially 
the  cutaneous  nerves  of  the  hands  and  feet;  and  on  branches  of  the 
large  sympathetic  plexus  about  the  abdominal  aorta  (Kolliker).  They 
often  occur  also  on  the  nerves  of  the  mesentery,  and  are  especially  well 
-seen  even  by  the  naked  eye  in  the  mesentery  of  the  cat.  They  have  been 
observed  also  in  the  pancreas,  lymphatic  glands  and  thyroid  glands,  as 


THE    NERVOUS    SYSTEM. 


461 


well  as  in  the  penis  of  the  cat.  Each  corpuscle  is  attached  by  a  narrow 
pedicle  to  the  nerve  on  which  it  is  situated,  and  is  formed  of  several 
concentric  layers  of  fine  membrane,  consisting  of  a  hyaline  ground-mem- 
brane with  connective-tissue  fibres,  each  layer  being  lined  by  endothe- 
lium (Fig.  320);  through  its  pedicle  passes  a  single  nerve-fibre,  which, 
after  traversing  the  several  concentric  layers  and  their  immediate  spaces, 
enters  a  central  cavity,  and,  gradually  losing  its  dark  border,  and  be- 
coming smaller,  terminates  at  or  near  the  distal  end  of  the  cavity,  in  a 


Fig.  318. 


Fir,.  310. 


Fig.  31R.— Extremities  of  a  nerve  of  the  finger  with  Pacinian  corpuscles  attached,  about  the  nat- 
ural size  (adapted  from  Henle  and  K<">lliker). 

Fig.  319.— Pacinian  corpuscle  of  the  cat's  mesentery.  The  stalk  consists  of  a  nerve-fibre  (N  I  with 
its  thick  outer  sheath.  The  peripheral  capsules  of  the  Pacinian  corpuscle  are  continuous  jwith  the 
outer  sheath  of  the  stalk.  The  intermediary  part  becomes  much  narrower  near  the  entrance  W  the 
axis-cylinder  into  the  clear  central  mass.  A  hook  shaped  termination  with  the  end-bulb  (T.)  is  seen 
in  the  upper  part.  A  blood-nessel  <  V  >  enters  the  Pacinian  corpuscle,  and  approaches  the  end-bulb; 
it  possesses  a  sheath  which  is  the  continuation  of  the  peripheral  capsules  of  the  Pacinian  corpuscle. 
X  100.    (Klein  and  Noble  Smith.) 


knob-like  enlargement,  or  m  a  bifurcation.  The  enlargement  com- 
monly found  at  the  end  of  the  fibre,  is  said  by  Pacini  to  resemble  a  gan- 
glion corpuscle;  but  this  observation  has  not  been  confirmed.  In  some 
cases  two  nerves  have  been  seen  entering  one  Pacinian  body,    and  in 


462 


HANDBOOK    OF    PHYSIOLOGY. 


others  a  nerve  after  passing  unaltered  through  one,  has  been  observed  to 
terminate  in  a  second  Pacinian  corpuscle.  The  physiological  import  of 
these  bodies  is  still  obscure. 


Fig.  330. 


Fig.  321. 


Fig.  322. 


Fig.  320. — Summit  of  a  Pacinian  corpuscle  of  the  human  finger,  showing  the  endothelial  mem- 
branes lining  the  capsules.     X  200.    (Klein  and  Noble  Smith.) 

Fig.  321.— A  corpuscle  of  Herbst,  from  the  tongue  of  a  duck,  a,  medullated  nerve  cut  away. 
<Klein.) 

Fig.  322.— End-bulb  of  Krause.    a,  medullated  nerve-fibre;    b,  capsule  of  corpuscle. 

(2.)  The  corpuscles  of  H erbst  (Fig.  321)  are  closely  allied  to  Pacinian 
corpuscles,  except  that  they  are  smaller  and  longer,  with  a  row  of  nu- 

B  A 


Fig.  323. — Papillae  from  the  skin  of  the  hand,  freed  from  the  cuticle  and  exhibiting  tactile 
■corpuscles,  a.  Simple  papilla  with  four  nerve-fibres;  a,  tactile  corpuscles;  b,  nerves,  b.  Papilla 
treated  with  acetic  acid;  a,  cortical  layer  with  cells  and  fine  elastic  filaments;  b,  tactile  corpuscle 
with  transverse  nuclei;  c,  entering  nerve  with  neurilemma  or  perineurium;  d,  nerve-fibres  winding 
round  the  corpuscle,     x  350.    (Kolliker.) 


clei  around  the  central  termination  of  the  nerve  in  the  core.     They  have 
been  found  chiefly  in  the  tongues  of  ducks.     The  capsules  are  nearer 


THE    NERVOUS    SYSTEM. 


463 


together,  and  towards  the  centre  the  endothelial  sheath  appears  to  be 
absent. 

(3.)  End-bulbs  are  found  in  the  conjunctiva,  in  the  glans  penis  and 
clitoris,  in  the  skin,  in  the  lips,  and  in  tendon;  each  is  about  -fa  inch 
in  diameter,  oval  or  spheroidal,  and  is  composed  of  a  medullated  nerve- 
fibre,  which  terminates  in  corpuscles  of  various  shapes,  with  a  capsule 
containing  a  transparent  or  striated  mass,  in  the  centre  of  which  termi- 


Fig.  324.  Fig.  325. 

Fig.  324.— A  corpuscle  of  Grandry,  from  the  tongue  of  a  duck. 
Fig.  325.— A  touch-corpuscle  of  Meissner,  from  the  skin  of  the  human  hand. 

nates  the  axis-cylinder  of  the  nerve-fibre,  the  ending  of  which  is  some- 
what clubbed  (Fig.  322). 

(4.)  Totich-corjmscles  (Fig.  323)  are  found  in  the  papillae  of  the  skin 
of  the  fingers  and  toes,  or  among  its  epithelium;  they  may  be  simple  or 


Fig.  326. 


Fig.  327. 


Fig.  328. 


Fig.  326.— Termination  of  medullated  nerve-fibres  in  tendon  near  the  muscular  insertion  (Golgi). 

Fig.  327.— One  of  the  reticulated  end-plates  of  Fig.  326,  more  highly  magnified,  a,  medullated 
nerve-fibre;  b,  reticulated  end-plates  (GolgO, 

Fig.  328.— A  termination  of  a  medullated  nerve-fibre  in  tendon,  lower  half  with  convoluted  me- 
dullated nerve-fibre  (Golgi,). 

compound;  when  simple,  they  are  large  and  slightly  flattened  transpar- 
ent nucleated  ganglion  cells,  inclosed  in  a  capsule;  when  compound  the 
capsule  contains  several  small  cells.  They  are  small  oblong  masses, 
about  -jly  inch  long,  and  7^ff  inch  broad.  Some  regard  touch-corpus- 
cles as  little  else  tl\m  masses  of  fibrous  or  connective  tissue,  surrounded 
by  elastic  fibres,  and  formed,  according  to  Huxley,  by  an  increased  de- 


4:64:  HANDBOOK   OF   PHYSIOLOGY. 

velopment  of  the  primitive  sheaths  of  the  nerve-fibres,  entering  the 
papillae.  Others,  however,  believe  that,  instead  of  thus  consisting  of  a 
homogeneous  mass  of  connective  tissue,  they  are  special  and  peculiar 
bodies  of  laminated  structure,  directly  concerned  in  the  sense  of  touch. 
They  do  not  occur  in  all  the  papillae  of  the  parts  where  they  are  found, 
and,  as  a  rule,  in  the  papillas  in  which  they  are  present  there  are  no 
blood-vessels.  Since  these  bodies  in  which  the  nerve-fibres  end  are  only 
met  with  in  the  papillae  of  highly  sensitive  parts,  it  is  inferred  that  they 
are  specially  concerned  in  the  sense  of  touch,  yet  their  absence  from  the 
papillae  of  other  tactile  parts  shows  that  they  are  not  essential  to  this 
sense. 

The  peculiar  way  in  which  the  medullated  nerve  winds  round  and 
round  the  corpuscle  before  it  enters  it  is  shown  in  Fig.  325. 

It  loses  its  sheath  before  it  enters  into  the  interior,  and  then  its  axis- 
cylinder  branches,  and  the  branches  coil  around  the  corpuscle  (Fig. 
325),  anastomosing  with  one  another  and  ending  in  pear-shaped  enlarge- 
ments. 

(5.)  The  corpuscles  of  Grandry  (Fig.  324),  form  another  variety,  and 
have  been  noticed  in  the  beaks  and  tongues  of  birds.  They  consist  of 
corpuscles  oval  or  spherical,  contained  within  a  nucleated  sheath,  and 
containing  several  cells,  two  or  more  compressed  vertically.  The  cells 
are  granular  and  transparent,  with  a  nucleus.  The  nerve  enters  on  one 
side,  and  laying  aside  its  medullary  sheath,  terminates  in  or  between  the 
cells. 

(6.)  Nerve  terminations,  probably  sensory  in  function,  are  found  in 
intermuscular  tissue  (Figs.  326,  327),  and  also  in  tendon.  The  former 
are  reticulated  end  plates,  and  the  latter  are  something  like  small  Paci- 
nian corpuscles  (Fig.  328). 

(7.)  In  addition  to  the  special  end  organs,  sensory  fibres  may  termi- 
nate in  plexuses,  as  in  the  sub-epithelial  and  the  intra-epithelial  plexus 
of  the  cornea. 

B.  Of  Nerves  of  Special  Sense. — The  terminations  of  the  nerves 
of  special  sense  will  be  considered  in  the  Chapter  on  the  Special  Senses. 

C.  Of  Motor  Nerves. — The  terminations  of  nerves  in  muscle,  both 
striped  and  unstriped,  have  been  already  described,  p.  398. 

D.  Of  Secretory  Nerves. — The  ending  of  nerves  in  the  cells  of  the 
salivary  glands  has  been  described  by  Pfliiger,  and  has  been  already 
alluded  to. 

III.  General  Plan  of  the  Construction  of  the  Nervous 

System. 

The  Nervous  System  is  made  up  of  two  portions  or  systems,  the  (I.) 
Cerebrospinal,  and  the  (II.)  Sympathetic. 

(I.)  The  Cerebro-spinal  System  includes  the  Brain — including 


THE    NERVOUS    SYSTEM.  465 

the  Cerebrum,  Cerebellum,  the  Crura  cerebri,  the  Pons  Varolii,  and  the 
so-called  Basic  ganglia;  the  Medulla  Oblongata;  and  the  Spinal  cord, 
with  the  nerves  proceeding  from  them.  Its  fibres  are  chiefly,  but  not 
exclusively,  distributed  to  the  skin  and  other  organs  of  the  senses,  and 
to  the  voluntary  muscles. 

(II.)  The  Sympathetic  System  consists  of: — (1)  A  double  chain 
of  ganglia  and  fibres,  which  extends  from  the  cranium  to  the  pelvis, 
along  each  side  of  the  vertebral  column,  and  from  which  branches  are 
distributed  both  to  the  cerebro-spinal  system,  and  to  other  parts  of  the 
sympathetic  system.  With  these  may  be  included  the  small  ganglia  in 
connection  with  those  branches  of  the  fifth  cerebral  nerve  which  are  dis- 
tributed in  the  neighborhood  of  the  organs  of  special  sense:  namely,  the 
Ophthalmic,  Otic,  Spheno -palatine,  and  Submaxillary  ganglia.  (2) 
Various  ganglia  and  plexuses  of  nerve-fibres  which  give  off  branches  to 
the  thoracic  and  abdominal  viscera,  the  chief  of  such  plexuses  being  the 
Cardiac,  Solar,  and  Hypogastric;  but  in  intimate  connection  with  these 
are  many  secondary  plexuses,  as  the  Aortic,  Spermatic,  and  Renal.  To 
these  plexuses,  fibres  pass  from  the  prevertebral  chain  of  ganglia,  as  well 
as  from  cerebro-spinal  nerves.  (3)  Various  ganglia  and  plexuses  in  the 
substance  of  many  of  the  viscera,  as  in  the  Stomach,  Intestines  and 
Urinary  bladder.  These,  which  are,  for  the  most  part,  microscopic,  also 
freely  communicate  with  other  parts  of  the  sympathetic  system,  as  well 
as,  to  some  extent,  with  the  cerebro-spinal.  (4)  By  many,  the  ganglia 
on  the  Posterior  roots  of  the  spinal  nerves,  on  the  Glossopharyngeal  and 
Vagus,  and  on  the  Sensory  root  of  the  Fifth  cerebral  nerve  (Gasserian 
ganglion),  are  also  included  as  sympathetic-nerve  structures. 

We  have  already  considered  the  functions  of  nerve-fibres;  we  must 
now  turn  to  those  of  the  Nerve-centres,  which  are  made  up  not  only  of 
nerve-fibres  but  also  of  nerve-cells. 

IV.  Functions  of  Nerve-Centres. 

The  functions  of  nerve-centres  may  be  classified  as  follows: — 1.  Con- 
duction. 2.  Transference.  3.  Reflection.  4.  Automatism.  5.  Aug- 
mentation.    6.  Inhibition. 

1.  Conduction. 

Conduction  in  or  through  nerve-centres  may  be  thus  simply  illus- 
trated. The  food  in  a  given  portion  of  the  intestines,  acting  as  a 
stimulus,  produces  a  certain  impression  on  the  nerves  in  the  mucous 
membrane,  which  impression  is  conveyed  through  them  to  the  adjacent 
ganglia  of  the  sympathetic.     In  ordinary  cases,  the  consequence  of  such 

an  impression  on  the  ganglia  is  the  movement   by  reflex   action  of  the 
30 


4t66  HANDBOOK   OF   PHYSIOLOGY. 

muscular  coat  of  that  and  the  adjacent  part  of  the  canal.  But  if  irritant 
substances  be  mingled  with  the  food,  the  sharper  stimulus  produces  a 
stronger  impression,  and  this  is  conducted  through  the  nearest  ganglia  to 
others  more  and  more  distant;  and,  from  all  these,  reflex  motor  impulses 
issuing,  excite  a  wide-extended  and  more  forcible  action  of  the  intestines. 
Or  even  through  the  sympathetic  ganglia, the  impression  maybe  further 
conducted  to  the  spinal  cord,  whence  may  issue  motor  impulses  to  the 
abdominal  and  other  muscles,  producing  cramp.  And  yet  further,  the 
same  morbid  impression  may  be  conducted  through  the  spinal  cord  to 
the  brain,  where  it  may  he  felt.  In  the  opposite  direction,  mental  influ- 
ence may  be  conducted  from  the  brain  through  a  succession  of  nervous 
centres — the  spinal  cord  and  ganglia,  and  one  or  more  ganglia  of  the 
sympathetic — to  produce  the  influence  of  the  mind  on  the  digestive 
and  other  organs;  altering  both  the  quantity  and  quality  of  their  secre- 
tions. 

2.  Transference. 

It  has  been  previously  stated  that  impressions  conveyed  by  any  cen- 
tripetal nerve-fibre  travel  uninterruptedly  throughout  its  whole  length, 
and  are  not  communicated  to  adjacent  fibres. 

When  such  an  impression,  however,  reaches  a  nerve-centre,  it  may 
seem  to  be  communicated  to  another  fibre  or  fibres;  as  pain  or  some  other 
kind  of  sensation  may  be  felt  in  a  part  different  altogether  from  that 
from  which,  so  to  speak,  the  stimulus  started.  Thus,  in  disease  of  the 
hip,  there  may  be  pain  in  the  knee.  This  apparent  change  of  place  of  a 
sensation  to  a  part  to  which  it  would  not  seem  properly  to  belong  is 
termed  transference. 

The  transference  of  impressions  may  be  illustrated  by  the  fact  just 
referred  to — the  pain  in  the  knee,  which  is  a  common  symptom  of  disease 
of  the  hip.  In  this  case  the  impression  made  by  the  disease  on  the 
nerves  of  the  hip-joint  is  conveyed  to  the  spinal  cord;  there  it  is  trans- 
ferred to  the  central  ends  or  connections  of  the  nerve-fibres  which  are 
distributed  about  the  knee.  Through  these  the  transferred  impression 
is  conducted  to  the  brain,  which,  referring  the  sensation  to  the  part  from 
which  it  usually  through  these  fibres  receives  impressions,  feels  as  if  the 
disease  and  the  source  of  pain  were  in  the  knee.  At  the  same  time 
that  it  is  transferred,  the  primary  impression  may  be  also  conducted  to 
the  brain;  and  in  this  case  the  pain  is  felt  in  both  the  hip  and  the  knee. 
And  so,  in  whatever  part  of  the  respiratory  organs  an  irritation  may  be 
seated,  the  impression  it  produces,  being  conducted  to  the  medulla  ob- 
longata, is  transferred  to  the  central  connections  of  the  nerves  of  the 
larynx;  and  thence,  being  conducted  as  in  the  last  case  to  the  brain, 
the  latter  perceives  the  peculiar  sensation  of  tickling  in  the  glottis, 
which  excites   the  act  of  coughing.     Or,  again,  when  the  sun's   light 


THE    NERVOUS    SYSTEM.  467 

falls  strongly  on  the  eye,  a  tickling  may  be  felt  in  the  nose,  exciting 
sneezing. 

A  variety  of  transference,  which  may  be  termed  radiation  of  impres- 
sions, is  shown  wheu  an  impression  received  by  a  nervous  centre  is  dif- 
fused to  many  other  parts  in  the  same  centre,  and  produces  sensations 
extending  far  beyond  the  part  from  which  the  primary  impression  was 
derived.  Hence,  as  in  the  former  cases,  result  various  kinds  of  what 
have  been  denominated  sympathetic  sensations.  Sometimes  such  sensa- 
tions are  referred  to  almost  every  part  of  the  body:  as  in  the  shock  and 
tingling  of  the  skin  produced  by  some  startling  noise.  Sometimes  only 
the  parts  immediately  surrounding  the  point  first  irritated  participate  in 
the  effects  of  the  irritation;  thus,  the  aching  of  a  tooth  may  be  accom- 
panied by  pain  in  the  adjoining  teeth,  and  in  all  the  surrounding  parts 
of  the  face;  the  explanation  of  such  a  case  being,  that  the  irritation 
conveyed  to  the  brain  by  the  nerve-fibres  of  the  diseased  tooth  is  radiated 
to  the  central  ends  of  adjoining  fibres,  and  that  the  mind  perceives  this 
secondary  impression  as  if  it  were  derived  from  the  peripheral  ends  of 
the  fibres. 

3.  Reflection. 

In  the  cases  of  transference  of  nerve-force  just  described,  it  has  been 
said  that  all  that  need  be  assumed  is  a  communication  of  the  excited 
condition  of  an  afferent  nerve  to  other  parts  of  its  nerve-centre  than 
that  from  which  it  takes  its  origin.  In  the  case  of  reflection,  on  the 
other  hand,  the  stimulus  having  been  conveyed  to  a  nerve-centre  by  a 
centripetal  nerve,  is  conducted  away  again  by  a  centrifugal  nerve,  and 
effects  some  change— motor,  secretory,  or  nutritive,  at  the  peripheral 
extremity  of  the  latter — the  difference  in  effect  depending  on  the  variety 
of  centrifugal  nerve  secondarily  affected.  As  in  transference,  the  reflec- 
tion may  take  place  from  a  certain  limited  set  of  centripetal  nerves  to  a 
corresponding  and  related  set  of  centrifugal  nerves;  as  when  in  conse- 
quence of  the  impression  of  light  on  the  retina,  the  iris  contracts,  but 
no  other  muscle  moves.  Or  the  reflection  may  extend  to  widely  different 
parts:  as  when  an  irritation  in  the  larynx  brings  all  the  muscles  engaged 
in  expiration  into  coincident  movement.  Keflex  movements,  occurring 
quite  independently  of  sensation,  are  generally  called  excito-motor; 
those  which  are  guided  or  accompanied  by  sensation,  but  not  to  the 
extent  of  a  distinct  perception  or  intellectual  process,  are  termed  sen- 
sori-vwtor. 

(a)  For  the  manifestation  of  every  reflex  action,  these  things  are  neces- 
sary: (1),  oue  or.  more  perfect  centripetal  nerve-fibres,  to  convey  an  im- 
pression; (2),  a  nervous  centre  for  its  reception,  and  by  which  it  may  be 
reflected;  (3).  oue  or  more  centrifugal  nerve-fibres,  along  which  the  im- 
pression may  be  conducted  to  (4),  the  muscular  or  other  tissue  bv  which 


46 S  HANDBOOK   OF    PHYSIOLOGY. 

the  effect  is  manifested.  Iu  the  absence  of  any  one  of  these  conditions, 
a  proper  reflex  action  cannot  take  place;  and  whenever,  for  example, 
impressions  made  by  external  stimuli  on  sensory  nerves  give  rise  to 
movements,  these  are  never  the  result  of  the  direct  reaction  of  the  sen- 
sory and  motor  fibres  of  the  nerves  on  each  other;  in  all  such  cases  the 
impression  is  conveyed  by  the  afferent  fibres  to  a  nerve-centre,  and  is 
therein  communicated  to  the  motor  fibres. 

(b)  All  reflex  actions  are  essentially  involuntary,  though  most  of 
them  admit  of  being  modified,  controlled,  or  prevented  by  a  voluntary 
effort. 

(c)  Keflex  actions  performed  in  health  have,  for  the  most  part,  a  dis- 
tinct purpose,  and  are  adapted  to  secure  some  end  desirable  for  the  well- 
being  of  the  body;  but,  in  disease,  many  of  them  are  irregular  and 
purposeless.  As  an  illustration  of  the  first  point,  may  be  mentioned 
movements  of  the  digestive  canal,  the  respiratory  movements,  and  the 
contraction  of  the  eyelids  and  the  pupil  to  exclude  many  rays  of  light, 
when  the  retina  is  exposed  to  a  bright  glare.  These  and  all  other  nor- 
mal reflex  acts  afford  also  examples  of  the  mode  in  which  the  nervous 
centres  combine  and  arrange  co-ordinately  the  actions  of  the  nerve-fibres, 
so  that  many  muscles  may  act  together  for  the  common  end.  Another 
instance  of  the  same  kind  is  furnished  by  the  spasmodic  contractions  of 
the  glottis  on  the  contact  of  carbonic  acid  gas,  or  any  foreign  substance, 
with  the  surface  of  the  epiglottis  or  larynx.  Examples  of  the  purpose- 
less irregular  nature  of  morbid  reflex  action  are  seen  in  the  convulsive 
movements  of  epilepsy,  and  in  the  spasms  of  tetanus  and  hydrophobia. 

(d)  Keflex  muscular  acts  are  often  more  sustained  than  those  produced 
by  the  direct  slimulus  of  muscular  nerves.  The  irritation  of  a  muscular 
organ,  or  its  motor  nerve,  produces  contraction  lasting  only  so  long  as 
the  irritation  continues;  but  irritation  applied  to  a  nervous  centre 
through  one  of  its  centripetal  nerves,  may  excite  reflex  and  harmonious 
contractions,  which  last  some  time  after  the  withdrawal  of  the  stimulus. 

Classification  of  Reflex  Actions. — Reflex  actions  may  be  classified 
as  follows: — 1.  Those  in  which  both  the  centripetal  and  centrifugal 
nerves  concerned  are  cerebrospinal;  e.g.,  deglutition,  sneezing,  coughing, 
and,  in  pathological  conditions,  tetanus,  epilepsy.  2.  Those  in  which 
the  centripetal  nerve  is  cerebrospinal,  and  the  centrifugal  is  sympathetic, 
most  often  vaso-motor;  e.g.,  secretion  of  saliva,  or  gastric  juice;  blushing 
or  pallor  of  the  skin.  3.  Those  in  which  the  centripetal  nerve  is  of  the 
sympathetic  system,  and  the  centrifugal  is  cerebrospinal.  The  majority 
of  these  are  pathological,  as  in  the  case  of  convulsion,  produced  by  intes- 
tinal worms,  or  hysterical  convulsions.  4.  Those  in  which  both  centrip- 
etal and  centrifugal  nerves  are  of  the  sympathetic  system:  as,  for  exam- 
ple, in  the  nervous  mechanism  concerned  in  the  secretion  of  the  intestinal 


THE    NERVOUS    SYSTEM.  4'i'.' 

fluids,  those  which  unite  the  various  generative  functions,  and  many 
pathological  phenomena. 

Relations  between  the  Stimulus  and  the  Resulting  Reflex 
Action. — Certain  rules  showing  the  relation  between  the  resulting  reflex 
action  and  the  stimulus  have  been  drawn  up  by  Pfliiger,  as  follows: — 

1.  Laiv  of  unilateral  reflection.  —A  slight  irritation  of  sensory  nerves 
is  reflected  along  the  motor  nerves  of  the  same  region.  Thus,  if  the 
skin  of  a  frog's  foot  be  tickled  on  the  right  side,  the  right  leg  is  drawn 
up. 

2.  Law  of  symmetrical  reflection. — A  stronger  irritation  is  reflected, 
not  only  on  one  side,  but  also  along  the  corresponding  motor  nerves  of 
the  opposite  side.  Thus,  if  the  spinal  cord  of  a  man  has  been  severed  by 
a  stab  in  the  back,  when  one  foot  is  tickled  both  legs  will  be  drawn  up. 

3.  Laiv  of  intensity. — Tn  the  above  case,  the  contractions  will  be  more 
violent  on  the  side  irritated. 

4.  Law  of  radiation. — If  the  irritation  (afferent  impulse)  increases, 
it  is  reflected  along  the  motor  nerves  which  spring  from  points  higher  up 
the  spinal  cord,  till  at  length  all  the  muscles  of  the  body  are  thrown  into 
action. 

Varieties  of  Reflex  Actions. 

Simple  and  Co-ordinated  Reflex  Actions. — In  the  simplest  form  of 
reflex  action  a  single  nerve  cell  with  an  afferent  and  an  efferent  fibre  is 
concerned,  but  in  the  majority  of  actual  actions  a  number  of  cells  are 
probably  concerned,  and  the  impression  is  as  it  were  distributed  among 
them,  and  they  act  in  concert  or  co-ordination.  This  co-ordinating 
power  belongs  to  nerve-centres. 

Primary  and  Secondary  or  acquired  Reflex  Actions. — We  must  care- 
fully distinguish  between  such  reflex  actions  which  may  be  termed  pri- 
mary, and  those  which  are  secondary  or  acquired.  As  examples  of  the 
former  class  we  may  cite  sucking,  contraction  of  the  pupil,  drawing  up 
the  legs  when  the  toes  are  tickled,  and  many  others,  which  are  per- 
formed as  perfectly  by  the  infant  as  by  the  adult. 

The  large  class  of  secondary  reflex  actions  consists  of  acts  which  re- 
quire for  their  first  performance,  and  many  subsequent  repetitions,  an 
effort  of  will,  but  which  by  constant  repetition  are  habitually  though 
not  necessarily  performed,  mechanically,  i.  e.,  without  the  intervention 
of  consciousness  and  volition.  As  instances  we  may  take  reading,  writ- 
ing, walking,  etc. 

In  endeavoring  to  conceive  how  such  complicated  actions  can  be  per- 
formed without  consciousness  and  will,  we  must  suppose  that  in  the  first 
instance  the  will  directs  the  nerve  force  along  certain  channels  causing 
the  performance  of  certain  acts,  e.  g.,  the  various  movements  of  flexion 
and  extension  involved  in  walking.     After  a  time  by  constant  repetition, 


470  HANDBOOK    OF    PHYSIOLOGY. 

these  routes  become,  to  use  a  metaphor,  well  worn  :  there  is,  as  it  were, 
a  beaten  track  along  which  the  nerve-force  travels  with  much  greater 
ease  than  formerly:  so  much  so  that  a  slight  stimulus,  such  as  the  pres- 
sure of  the  foot  on  the  ground,  is  sufficient  to  start  and  keep  going  in- 
definitely the  complex  reflex  actions  of  walking  during  entire  mental 
abstraction,  or  even  during  sleep.  In  such  acts  as  reading,  writing,  and 
fne  like,  it  would  appear  as  if  the  will  set  the  necessary  reflex  machinery 
going,  and  that  the  reflex  actions  go  on  uninterruptedly  until  again  in- 
terfered with  by  the  will. 

Without  this  capacity  possessed  by  the  nervous  system  of  "  organiz- 
ing conscious  actions  into  more  or  less  unconscious  ones/'  education  or 
training  would  be  impossible.  A  most  important  part  of  the  process  by 
which  these  acquired  reflex  actions  come  to  be  performed  automatically 
consists  in  what  is  termed  association.  If  two  acts  be  at  first  performed 
voluntarily  in  succession,  and  this  succession  is  often  repeated,  the  per- 
formance of  the  first  is  at  once  followed  mechanically  by  the  second. 
Instances  of  this  "  force  of  habit  "  must  be  within  the  daily  experience 
of  every  one. 

Of  course  it  is  only  such  actions  as  have  become  entirely  reflex  that 
can  be  performed  during  complete  unconsciousness,  as  in  sleep.  Cases 
of  somnambulism  are  of  course  familiar  to  every  one,  and  authentic  in- 
stances are  on  record  of  persons  writing,  and  even  playing  the  piano  dur- 
ing sleep. 

4.  Automatism. 

To  nerve  centres,  it  is  said,  belongs  the  property  of  originating 
nerve-impulses,  as  well  as  of  receiving  them,  and  conducting  and  reflect- 
ing them. 

The  term  automatism  is  employed  to  indicate  the  origination  of  ner- 
vous impulses  in  nerve-centres,  and  their  conduction  therefrom,  inde- 
pendently of  previous  reception  of  a  stimulus  from  another  part.  It  is 
impossible,  in  the  present  state  of  our  knowledge,  to  say  definitely  what 
actions  in  the  body  are  really  in  this  sense  automatic.  An  example  of 
automatic  nerve-action  has  been  already  referred  to,  i.  e.,  that  of  the 
respiratory  ceutre,  but  the  apparently  best  examples  of  automatism  are 
found,  however,  in  the  case  of  the  cerebrum,  which  will  be  presently 
considered. 

5  and  6.  Augmentation  and  Inhibition. 

Nerve-cells  not  only  receive  and  reflect  nerve  impulses,  and  also  in 
some  cases  even  originate  such  impulses,  but  they  are  also  capable  of  in- 
creasing the  impulse,  and  the  result  is  what  is  called  augmentation;  and 
when  a  nerve-centre  is  in  action,  its  action  is  also  capable  of  being  in- 


THE    NERVOUS    SYSTEM. 


471 


creased  or  diminished  {inhibition)  by  afferent  impulses.  This  is  the 
case  in  whatever  way  the  centre  has  caused  the  action,  whether  of  itself, 
or  by  means  of  previous  afferent  impulses.  The  action,  by  which  a 
centre  is  capable  of  being  inhibited  or  exalted,  has  been  well  shown  in 
the  case  of  the  vaso-motor  centre,  before  described.  This  power,  which 
can  be  exerted  from  the  periphery,  is  very  important  in  regulating  the 
action  even  of  partially  automatic  centres  such  as  the  respiratory  centre. 


CHAPTER   XVIII. 

THE  CEREBROSPINAL  NERVOUS    SYSTEM. 

The  physiology  of  the  cerebro-spinal  nervous  system  includes  that  of 
the  Spinal  Cord,  Medulla  Oblongata,  and  Brain,  of  the  several  Nerves 
given  off  from  each,  and  of  the  Ganglia  on  those  nerves. 

Membranes  of  the  Brain  and  Spinal  Cord.— The  Brain  and 
Spinal  Cord  are  enveloped  in  three  membranes — (1)  the  Dura  Mater,  (2) 
the  Arachnoid,  (3)  the  Pia  Mater. 

(1.)  The  Dura  Mater,  or  external  covering,  is  a  tough  membrane 
composed  of  bundles  of  connective  tissue  which  cross  at  various  angles, 
and  in  whose  interstices  branched  connective-tissue  corpuscles  lie;  it  is 
lined  by  a  thin  elastic  membrane,  and  on  the  inner  surface,  and,  where 
it  is  not  adherent  to  the  bone,  on  the  outer  surface  also,  is  a  layer  of  en- 
dothelial cells  very  similar  to  those  found  in  serous  membranes.  (2.) 
The  Arachnoid  is  a  much  more  delicate  membrane,  very  similar  in  struc- 
ture to  the  dura  mater,  and  lined  on  its  outer  or  free  surface  by  an  en- 
dothelial membrane.  (3.)  The  Pia  Mater  consists  of  two  chief  layers, 
between  which  numerous  blood-vessels  ramify.  Between  the  arachnoid 
and  pia  mater  is  a  network  of  fibrous-tissue  trabecule  sheathed  with  en- 
dothelial cells;  these  sub-arachnoid  trabecule  divide  up  the  sub-arach- 
noid space  into  a  number  of  irregular  sinuses.  There  are  some  similar 
trabecule,  but  much  fewer  in  number,  traversing  the  sub-dural  space, 
i.  e.,  the  space  between  the  dura  mater  and  arachnoid. 

Pacchionian  bodies  are  growths  from  the  sub-arachnoid  network  of 
connective-tissue  trabeculae  which  project  through  small  holes  in  the 
inner  layers  of  the  dura  mater  into  the  venous  sinuses  of  that  membrane. 
The  venous  sinuses  of  the  dura  mater  have  been  injected  from  the 
sub-arachnoidal  space  through  the  intermediation  of  these  villous  out- 
'growths. 

A.    The  Spinal  Cord  and  its  Nerves. 

The  spinal  cord  is  a  cylindriform  column  of  nerve-substance  con- 
nected above  with  the  brain  through  the  medium  of  the  medulla  oblon- 
gata, and  terminating  below,  about  the  lower  border  of  the  first  lumbar 
vertebra,  in  a  slender  filament  of  gray  substance,  the  filum  terminale, 
which  lies  in  the  midst  of  the  roots  of  many  nerves  forming  the  cauda 
equina. 

Structure. — The  cord  is  composed  of  white  and  gray  nervous  sub- 
stance, of  which  the  former  is  situated  externally,   and  constitutes  its 


THE    CEREBROSPINAL    NERVOUS    SYSTEM. 


47 


chief  portion,  while  the  latter  occupies  its  central  or  axial  portion,  and 
is  so  arranged,  that  on  the  surface  of  a  transverse  section  of  the  cord  it 
appears  like  two  somewhat  cresceutic  masses  connected  together  by  a 


Pons  Vfrro2i..-V,A?j 
Medall.  Obiony^ 
CcrtMLum — .r'CfSS 


of.  S/iit-Ue.1  Cork 


1st.  DorsaL 
Vertebra. 


1st  Lumba 
ybftr.fr/-u 


LowcrExtremity  -  - 
of  Sfiinal  Cord. 


Fig.  329.— View  of  the  e-rebro  spinal  axis  of  the  nervous  system.  The  right  half  of  the  cranium 
and  trunk  of  the  body  has  been  removed  by  a  vertical  section;  the  membranes  of  the  brain  and 
spinal  cord  have  also  been  removed,  and  the  roots  and  first  part  of  the  fifth  and  ninth  cranial,  and 
of  all  the  spinal  nerves  of  the  right  side,  have  been  dissected  out  and  laid  separately  on  the  wan  or 
the  skull  and  on  the  several  vertebrae  opposite  to  the  place  of  their  natural  exit  from  the  cranio- 
spinal cavity.    (After  Bourgery.) 

narrower  portion,  or  isthmus  (Fig.  330).     Passing  through  the  centre 
of  this  isthmus  in  a  longitudinal  direction  is  a   minute  canal  (central 


471 


HANDBOOK    OF    PHYSIOLOGY. 


canal),  which  is  continued  through  the  whole  length  of  the  cord,  and 
opens  above  into  the  space  at  the  back  of  medulla  oblongata  and  pons 
Varolii,  called  the  fourth  ventricle.  It  is  lined  by  a  layer  of  columnar 
ciliated  epithelium. 

The  spinal  cord  consists  of  two  exactly  symmetrical  halves,  separated 
anteriorly  and  posteriorly  by  vertical  -fissures  (the  posterior  fissure  being 
deeper,  but  less  wide  and  distinct  than  the  anterior),  and  united  in  the 
middle  by  nervous  matter,  which  is  usually  described  as  forming  two 
commissures — an  anterior  commissure,  in  front  of  the  central  canal  con- 
sisting of  medullated  nerve-fibres,  and  a  posterior  commissure  behind 
the  central  canal,  consisting  also  of  medullated  nerve-fibres,  but  with 


Fig.  330.— Different  views  of  a  portion  of  the  spinal  cord  from  the  cervical  region,  with  the 
roots  of  the  nerves  (slightly  enlarged).  In  a,  the  anterior  surface  of  the  specimen  is  shown;  the 
anterior  nerve-root  of  its  right  side  being  divided;  in  b,  a  view  of  the  right  side  is  given;  in  c,  the 
upper  surface  is  shown;  in  d,  the  nerve-roots  and  ganglion  are  shown  from  below.  1.  The  anterior 
median  fissure ;  2,  posterior  median  fissure;  3,  anterior  lateral  depression,  over  which  the  anterior 
nerve-roots  are  seen  to  spread;  4,  posterior  lateral  groove,  into  which  the  posterior  roots  are  seen 
to  sink;  5,  anterior  roots  passing  the  ganglion;  5',  in  a.  the  anterior  root  divided;  6,  the  posterior 
roots,  the  fibres  of  which  pass  into  the  ganglion  6';  7,  the  united  or  compound  nerve;  7',  the  poste- 
rior primary  branch,  seen  in  a  and  u  to  be  derived  in  part  from  the  anterior  and  in  part  from  the 
posterior  root.    (Allen  Thomson.; 


more  neuroglia,  which  gives  the  gray  aspect  to  this  commissure  (Fig. 
330,  b).  Each  half  of  the  spinal  cord  is  marked  on  the  sides  (obscurely 
at  the  lower  part,  but  distinctly  above)  by  two  longitudinal  furrows, 
which  divide  it  into  three  portions,  columns,  or  tracts,  an  anterior, 
lateral,  and  posterior.  From  the  groove  between  the  anterior  and  lateral 
columns  spring  the  anterior  roots  of  the  spinal  nerves  (b  and  0,  5);  and 
just  in  front  of  the  groove  between  the  lateral  and  posterior  column  arise 


THE    CEREBROSPINAL    NERVOUS    SYSTEM. 


47 


.  .»■ 


the  posterior  roots  of  the  same  (b,  6);  a  pair  of  roots  on  each  side  cor- 
responding to  each  vertebra  (Fig.  329). 

White  matter. — The  white  matter  of  the  cord  is  made  up  of  me- 
dullated  nerve-fibres  of  various  sizes,  arranged  longitudinally  around  the 
cord  under  the  pia  mater,  aud  passing  in  to  support  the  individual  fibres 
in  the  delicate  connective  tissue  or  neuroglia  made  up  of  a  very  fine  re- 
ticulum, with  both  small  cells  almost  filled  up  by  nuclei  and  stellate 
branching  corpuscles. 

The  general  rule  respecting  the  size  of  different  parts  of  the  cord 
appears  to  be,  that  the  size  of  each  part  bears  a  direct  proportion  to  the 
size  and  number  of  nerve-roots  given  off  from  itself,  and  has  but  little 
relation  to  the  size  or  number  of  those  given  off  below  it.     Thus  the 


4mmmm 


mBSm 


!/.&. 


Fig.  331.— Section  of  gray  matter  of  anterior  cornu  of  a  calf's  spinal  cord;  n  f,  nerve-fibres  of 
white  matter  in  transverse  section,  showing  axis-cylinder  in  centre  of  each;  a  r,  anterior  roots  of 
spinal  nerve  passing  out  through  white  matter;  y  c,  large  stellate  nerve-cells  with  nuclei:  they  are 
seen  imbedded  in  neuroglia.    (Schofleld.j 

cord  is  very  large  in  the  middle  and  lower  part  of  its  cervical  portion, 
whence  arise  the  large  nerve-roots  for  the  formation  of  the  brachial 
plexuses  and  the  supply  of  the  upper  extremities,  and  again  enlarges 
at  the  lowest  part  of  its  dorsal  portion  and  the  upper  part  of  its  lum- 
bar, at  the  origins  of  the  large  nerves  which,  after  forming  the  hi  ml  inl- 
and sacral  plexuses,  are  distributed  to  the  lower  extremities.  The  chief 
cause  of  the  greater  size  at  these  parts  of  the  spinal  cord  is  increase  in 
the  quantity  of  gray  matter;  for  there  seems  reason  to  believe  that  the 
white  or  fibrous  part  of  the  cord  becomes  gradually  and  progressive!- 
larger  from  below  upwards,  doubtless  from  the  addition  of  a  certain  num- 
ber of  upward  passing  fibres  from  each  pair  of  nerves. 

From  careful  estimates  of  the  number  of  nerve-fibres  in  a  trans 


4r'<0  HANDBOOK    OF    PHYSIOLOGY. 

section  of  the  cord  towards  its  upper  end,  and  the  number  entering  it 
by  the  anterior  and  posterior  roots  of  each  pair  of  nerves,  it  has  been 
shown  that  in  the  human  spinal  cord  not  more  than  half  of  the  total 
number  of  nerve-fibres  entering  the  cord  through  all  the  spinal  nerves 
^re  contained  in  a  transverse  section  near  its  upper  end.  It  is  obvious, 
therefore,  that  at  least  half  of  the  nerve-fibres  entering  it  must  terminate 
in  the  cord  itself. 

Gray  matter. — The  gray  matter  of  the  cord  consists  essentially  of 
an  extremely  delicate  network  of  the  primitive  fibrillar  of  axis-cylinders, 
and  which  are  derived  from  the  ramification  of  multipolar  ganglion  cells 
of  very  large  size,  containing  large  round  nuclei  with  nucleoli.  This 
fine  plexus  is  called  Gerlach's  network,  and  is  mingled  with  the  meshes 


Fig.  332.— Transverse  section  of  half  the  spinal  cord  in  the  lumbar  enlargement  (semi-diagram- 
matic). 1.  Anterior  median  fissure;  2,  posterior  median  fissure;  3,  central  canal  lined  with  epithe- 
lium; 4,  posterior  commissure;  5,  anterior  commissure ;  6,  posterior  column;  7,  lateral  column;  8, 
anterior  column.  The  white  substance  is  traversed  by  radiating  trabeculae  of  pia  mater.  9,  Fasci- 
culus of  posterior  nerve-root  entering  in  one  bundle;  10,  fasciculi  of  anterior  roots  entering  in  four 
spreading  bundles  of  fibres;  b,  in  the  cervix  cornu,  decussating  fibres  from  the  nerve-roots  and  pos- 
terior commissure ;  c,  posterior  vesicular  columns.  About  half  way  between  the  central  canal  and 
7  are  seen  the  group  of  nerve- cells  forming  the  tractus  intermedio-lateralis;  e,  e,  fibres  of  anterior 
roots;  e\  fibres  of  anterior  roots  which  decussate  in  anterior  commissure.    (Allen  Thomson.)    v  6. 


of  neuroglia,  which  in  some  parts  is  chiefly  fibrillated,  in  others  mainly 
granular  and  punctiform.  The  neuroglia  is  prolonged  from  the  sur- 
face into  the  tip  of  the  posterior  cornu  of  gray  matter  and  forms  a 
jelly-like  transparent  substance,  which,  when  hardened,  is  found  to  be 
reticular,  and  is  called  the  substantia  gelatinosa  of  Eolando. 

The  multipolar  cells  are  either  scattered  singly  or  arranged  in  groups, 
of  which  the  following  are  to  be  distinguished  on  either  side: — (a)  In  the 
anterior  cornu.  The  groups  found  in  the  anterior  cornu  are  generally 
two — one  at  the  lateral  part  near  the  lateral  column,  and  the  other  at 


THE    CEREBROSPINAL    NERVOUS    SYSTEM.  47T 

the  tip  of  the  cornu  iu  the  middle  line — sometimes,  as  in  the  lumbar  en- 
largement, there  is  a  third  group  more  posterior.  The  cells  of  the  an- 
terior group  are  the  largest.  Into  many  of  these  cells  the  fibres  of  the 
anterior  motor  nerve-roots  can  be  distinctly  traced,  (b)  In  the  tractus 
inter medio-later alls.  A  group  of  nerve-cells  midway  between  the  ante- 
rior and  posterior  cornua,  near  the  external  surface  of  the  gray  matter. 
It  is  especially  developed  in  the  dorsal,  and  also  in  the  upper  cervical  re- 
gion, (c)  In  the  posterior  vesicular  columns  of  Lockhart  Clarke.  These 
are  found  in  the  posterior  cornua  of  gray  matter  towards  the  inner  sur- 
face, extending  from  the  cervical  enlargement  to  the  third  lumbar  nerves 
(Fig.  332,  c).  (d)  Smaller  cells  are  scattered  throughout  the  gray  mat- 
ter, but  are  found  chiefly  at  the  tip  (caput  cornu)  of  posterior  cornu,  in 
a  finely  granular  basis,  and  also  among  the  posterior  root  fibres  (substan- 
tia gelutinosa  cinerea  of  Rolando). 

The  anterior  nerve-cells  are  connected  by  their  processes  immediately 
with  the  axis-cylinders  of  the  fibres  of  the  anterior  or  motor  nerve-roots: 
whereas  the  nerve-cells  of  the  posterior  roots  are  connected  with  nerve- 
fibres,  not  directly,  but  only  through  the  intermediation  of  Gerlach's 
nerve-network,  in  which  their  branching  processes  lose  themselves. 

Spinal  Nerves. — The  spinal  nerves  consist  of  thirty-one  pairs,  issu- 
ing from  the  sides  of  the  whole  length  of  the  cord,  their  number  corre- 
sponding with  the  intervertebral  foramina  through  which  they  pass.  Each 
nerve  arises  by  two  roots,  an  anterior  and  posterior,  the  latter  being  the 
larger.  The  roots  emerge  through  separate  apertures  of  the  sheath  of 
dura  mater  surrounding  the  cord;  and  directly  after  their  emergence, 
where  the  roots  lie  in  the  intervertebral  foramen,  a  ganglion  is  found  on 
the  posterior  root.  The  anterior  root  lies  in  contact  with  the  anterior 
surface  of  the  ganglion,  but  none  of  its  fibres  intermingle  with  those  in 
the  ganglion  (5,  Fig.  330).  But  immediately  beyond  the  ganglion  the 
two  roots  coalesce,  and  by  the  mingling  of  their  fibres  forma  compound 
or  mixed  spinal  nerve,  which,  after  issuing  from  the  intervertebral  canal, 
gives  off  anterior  and  posterior  or  ventral  and  dorsal  branches,  each 
containing  fibres  from  both  the  roots  (Fig.  330),  as  well  as  a  third  or 
visceral  branch,  ramus  cotnmunicans,  to  the  sympathetic. 

The  anterior  root  of  each  spinal  nerve  arises  by  numerous  separate 
and  converging  bundles  from  the  anterior  column  of  the  cord;  the  pos- 
terior root  by  more  numerous  parallel  bundles,  from  the  posterior  column, 
or,  rather,  from  the  posterior  part  of  the  lateral  column  (Fig.  330),  for 
if  a  fissure  be  directed  inwards  from  the  groove  between  the  middle  and 
posterior  columns,  the  posterior  roots  will  remain  attached  to  the  for- 
mer. The  anterior  roots  of  each  spinal  nerve  consist  of  centrifugal  fibres; 
the  posterior  as  exclusively  of  centripetal  fibres. 

Course  of  the  Fibres  of  the  Spinal  Nerve-Roots,  (a)  The  An- 
terior roots  enter  the  cord  in  several  bandies,  which  may  be  called: — 


47S  HANDBOOK    OF    PHYSIOLOGY. 

(1)  Internal;  (2)  Middle;  (3)  External;  all  being  more  or  less  connected 
with  the  groups  of  multipolar  cells  in  the  anterior  cornua.  1.  The  in- 
ternal fibres  are  partly  connected  with  internal  group  of  nerve-cells  of 
anterior  cornu  of  the  same  side;  but  some  fibres  pass  over,  through  an- 
terior commissure  to  end  in  the  anterior  cornu  of  opposite  side,  proba- 
bly in  internal  group  of  cells.  2.  The  middle  fibres  are  partly  in 
connection  with  the  lateral  group  of  cells  in  anterior  cornu,  and  in  part 
pass  backwards  to  posterior  cornu,  having  no  connection  with  cells.  3. 
The  external  fibres  are  partly  in  connection  with  the  lateral  group  of 
cells  in  the  anterior  cornu,  but  some  fibres  proceed  direct  into  the  lateral 
column  without  connection  with  cells,  and  pass  upwards  in  it. 

(b)  The  Posterior  roots  enter  the  posterior  cornua  in  two  chief  bun- 
dles, either  at  the  tip,  through  or  round  the  substantia  gelatinosa,  or  by 
the  inner  side.  The  former  enter  the  gray  matter  at  once,  and  as  a 
rule,  turn  upwards  or  downwards  for  a  certain  distance  and  then  pass 
horizontally;  some  fibres  reach  the  anterior  cornua,   passing  at   once 


Atob-jrnot.       (!■•]>.  t 


P.root        P.H.C. 


Fig.  333.— Diagram  of  the  spinal  cord  at  the  lower  cervical  region  to  show  the  track  of  fibres; 
■d.p.  t.,  direct  pyramidal  tract;  l.  p.  t.,  crossed  pyramidal  tract;  d.  c.  t.,  direct  cerebellar  tract; 
p.  m.  c,  posterior  median  column.  A.  G.  F.,  anterior  ground  fibres;  A.  c,  anterior  commissure; 
P.  c,  post  commissure;  a.  l.  a.  t.,  antero-lateral  ascending  tract;  Ant.  C,  anterior  cornu;  P.  Cor., 
posterior  cornu;  c.  c.  p.,  intermediate  gray  substance;  l.  l.  l.,  lateral  limiting  layer.  (After  Gow- 
■ers.) 

horizontally;  and  the  others,  the  opposite  side,  through  the  posterior 
gray  commissure.  Of  those  which  enter  by  the  inner  side  of  the  cornua 
the  majority  pass  up  (or  down)  in  the  white  substance  of  the  posterior 
columns,  and  enter  the  gray  matter  at  various  heights  at  the  base  of  the 
posterior  cornu;  perhaps  some  pass  directly  upwards  and  inwards  in  the 
posterior  median  column  with^"4"  enteric  tLs  gray  matter.  Those 
that  enter  the  gray  matter  pass  in  various  directions,  some  to  join  the 
lateral  cells  in  the  anterior  cornu,  some  join  the  cells  in  the  posterior 
vesicular  column,  and  some  pass  across  to  the  other  side  of  the  cord  in 
the  anterior  commissure,  whilst  others  become  again  longitudinal  in  the 
gray  matter. 

It  should  be  here  mentioned  that  the  cells  in  the  posterior  vesicular 
column  are  connected  with  medullated  fibres  which  pass  horizontally  to 
the  white  matter  of  the  lateral  columns,  and  there  become  longitudinal. 


THE    CEREBROSPINAL    NERVOUS    SYSTEM.  47'' 

Course  of  the  fibres  in  the  cord.  The  nerve-fibres  which  form  the 
white  matter  of  the  cord  are  nearly  all  longitudinal  fibres.  It  is,  how- 
ever, a  matter  of  great  difficulty  to  trace  them  by  mere  dissection,  and 
so  other  methods  have  been  resorted  to.  One  of  these  is  based  upon  the 
fact  that  nerve-fibres  undergo  degeneration  when  they  are  cut  off  from 
the  centre  with  which  they  are  normally  connected,  or  when  the  parts 
to  which  they  are  distributed  are  removed,  as  in  amputation  of  a  limb; 
and  information  as  to  the  course  of  the  fibres  has  been  obtained  by  trac- 
ing such  degenerated  tracts.  The  second  method  consists  in  observing 
the  development  of  the  fibres  of  the  various  tracts;  some  tracts  of  fibres 
receive  their  medullary  substance  later  than  others,  and  are  to  be  traced 
by  their  gray  appearance.  The  chief  tracts  which  have  been  made  out 
are  the  following: — (1)  The  direct  pyramidal  tract  (Fig.  333,  d,  p,  t),  a 
comparatively  small  portion  of  the  inner  part  of  the  anterior  columns, 
which  is  traceable  from  the  anterior  pyramids  of  the  medulla,  as  far  as 
the  mid-dorsal  region  of  the  spinal  cord.  It  consists  of  the  fibres  of  the 
pyramids  which  do  not  undergo  decussation  in  the  medulla.  They  are 
probably  fibres  chiefly  for  the  arm  and  constitute  about  one-fourth  or 
one-fifth  of  the  whole  motor  tract.  There  is  reason  for  believing,  how- 
ever, that  the  fibres  of  this  tract  uudergo  decussation  throughout  their 
coarse,  and  also  that  fibres  pass  over  from  it  through  the  anterior  com- 
missure to  join  the  lateral  pyramidal  tract;  (2)  the  Crossed  or  lateral  pyra- 
midal tract  (Fig.  333,  l.  p.  t.)  can  be  traced  from  the  anterior  pyra- 
mids of  the  medulla,  and  consists  of  motor  fibres  which  decussate  in  the 
anterior  fissure  and  pass  downwards  in  the  lateral  columns  near  the 
posterior  cornu  of  the  gray  matter.  They  may  be  traced  downwards  as 
far  as  the  lower  end  of  the  cord.  The  number  of  fibres  which  decussate 
in  the  medulla,  and  consequently  the  size  of  this  tract,  varies.  The 
fibres  which  most  constantly  cross  over  are  those  for  the  leg.  The  pyra- 
midal tracts  end  in  the  gray  matter  of  the  anterior  cornua;  (3)  Direct 
cerebellar  tract,  D.  c.  t.,  which  corresponds  to  the  peripheral  portion  of 
the  posterior  lateral  column  between  the  crossed  pyramidal  tract  and 
the  edge  of  the  cord,  can  be  traced  upwards  directly  to  the  cerebellum 
aud  downwards  as  far  as  the  mid-lumbar  region;  (4)  Posterior  median 
column  or  Fasciculus  of  Goll,  is  found  on  either  side  of  the  posterior 
commissure,  and  is  traceable  upwards  and  terminates  as  the  fasciculus 
gracilis  of  the  medulla.  It  is  traceable  downwards  as  far  as  the  mid- 
dorsal  region.  The  portion  of  the  posterior  column  between  the  poste- 
rior median  column  and  the  posterior  roots  of  the  spinal  nerves,  known 
as  (5)  the  Fasciculus  cuneatus,  Burdach's,  or  Postero-external  column, 
is  composed  of  fibres  of  the  posterior  roots  on  their  way  to  enter  the  gray 
substance  aud  the  posterior  median  column  at  different  heights.  The 
antero-lateral  column  contains  fibres  from  the  anterior  cornua  of  the 
same  as  well  as  of  the  opposite  side;  (G)  Lateral  limiting  layer  (l.  l.  L.) 


480  HANDBOOK    OF    PHYSIOLOGY. 

consists  of  fine  fibres  which,  pass  into  the  gray  matter  at  different  levels; 
it  probably  consists  of  connecting  fibres  to  connect  the  gray  matter  of 
different  levels.  These  fibres  have  not  a  long  course;  (7)  Anterior 
ground  fibres  (a.  g.  f.)  are  vertical  fibres  which  probably  connect  the 
anterior  cornua  at  different  levels.  Some  fibres  pass  to  the  anterior 
commissure  and  connect  with  the  anterior  cornu  of  the  opposite  side; 
(8)  Antero-lateral  ascending  tract  is  a  tract  which  degenerates  upwards. 
It  is  a  sensory  tract,  and  is  connected  with  the  posterior  nerve-roots  of 
the  opposite  side. 

Functions  of  the  Spinal  Nerve-Roots. — The  anterior  spinal 
nerve-roots  are  efferent  or  motor:  the  posterior  are  afferent  or  sensory. 
The  fact  is  proved  in  various  ways.  Division  of  the  anterior  roots  of 
one  or  more  nerves  is  followed  by  complete  loss  of  motion  in  the  parts 
supplied  by  the  fibres  of  such  roots;  but  the  sensation  of  the  same  parts 
remains  perfect.  Division  of  the  posterior  roots  destroys  the  sensibility 
of  the  parts  supplied  by  their  fibres,  while  the  power  of  motion  continues 
unimpaired.  Moreover,  irritation  of  the  ends  of  the  distal  portions  of 
the  divided  anterior  roots  of  a  nerve  excites  muscular  movements;  irri- 
tation of  the  ends  of  the  proximal  portions,  which  are  still  in  connection 
with  the  cord,  is  followed  by  no  appreciable  effect.  Irritation  of  the 
distal  portions  of  the  divided  posterior  roots,  on  the  other  hand,  pro- 
duces no  muscular  movements  and  no  manifestations  of  pain;  for,  as 
already  stated,  sensory  nerves  convey  impressions  only  towards  the  nerv- 
ous centres:  but  irritation  of  the  proximal  portions  of  these  elicits  signs 
of  intense  suffering.  Occasionally,  under  this  last  irritation,  muscular 
movements  also  ensue;  but  these  are  either  voluntary,  or  the  result  of 
the  irritation  being  reflected  from  the  sensory  to  the  motor  fibres. 
Occasionally,  too,  irritation  of  the  distal  ends  of  divided  anterior  roots 
elicits  signs  of  pain,  as  well  as  producing  muscular  movements:  the  pain 
thus  excited  is  probably  the  result  either  of  cramp  or  of  so-called  recur- 
rent sensibility. 

Recurrent  Sensibility. — If  the  anterior  root  of  a  spinal  nerve  be 
divided,  and  the  peripheral  end  be  irritated,  not  only  movements  of  the 
muscles  supplied  by  the  nerve  take  place,  but  also  of  other  muscles,  in- 
dicative of  pain.  If  the  main  trunk  of  the  nerve  (after  the  coalescence 
of  the  roots  beyond  the  ganglion)  be  divided,  and  the  anterior  root  be 
irritated  as  before,  the  general  signs  of  pain  still  remain,  although  the 
contraction  of  the  muscles  does  not  occur.  The  signs  of  pain  disappear 
when  the  posterior  root  is  divided.  -From  these  experiments  it  is  be- 
lieved that  the  stimulus  passes  down  the  anterior  root  to  the  mixed  nerve, 
and  returns  to  the  central  nervous  system  through  the  posterior  root  by 
means  of  certain  sensory  fibres  from  the  posterior  root,  which  loop  back 
into  the  anterior  root  before  continuing  their  course  into  the  mixed 
nerve-trunk. 


THE    CEREBROSPINAL    NERVOUS    SYSTEM.  481 

Functions  of  the  Ganglia  on  Posterior  Roots. — The  ganglia  act  as 
centres  for  the  nutrition  of  the  nerves,  since  when  the  nerves  are  severed 
from  connection  with  the  ganglia,  the  parts  of  the  nerves  so  severed 
degenerate,  whilst  the  parts  which  remain  in  connection  with  them  do 
not. 

Functions  of  the  Spinal  Cord. 

The  power  of  the  spinal  cord,  as  a  nerve-centre,  may  be  arranged 
under  the  heads  of  (1)  Conduction;  (2)  Transference;  (3)  Keflex  action. 

(1)  Conduction. — The  functions  of  the  spinal  cord  in  relation  to  con- 
duction, may  be  best  remembered  by  considering  its  anatomical  connec- 
tions with  other  parts  of  the  body.  From  these  it  is  evident  that,  with 
the  exception  of  some  few  filaments  of  the  sympathetic,  there  is  no  way 
by  which  nerve-impulses  can  be  conveyed  from  the  trunk  and  extremi- 
ties to  the  brain,  or  vice  versa,  other  than  that  formed  by  the  spinal 
cord.  Through  it,  the  impressions  made  upon  the  peripheral  extremi- 
ties or  other  parts  of  the  spinal  sensory  nerves  are  conducted  to  the 
brain,  where  alone  they  can  he  perceived.  Through  it,  also,  the  stimulus 
of  the  will,  conducted  from  the  brain,  is  capable  of  exciting  the  action 
of  the  muscles  supplied  from  it  with  motor  nerves.  And  for  all  these 
conductions  of  impressions  to  and  fro  between  the  brains  and  the  .spinal 
nerves,  the  perfect  state  of  the  cord  is  necessary;  for  when  any  part  of  it 
is  destroyed,  and  its  communication  with  the  brain  is  interrupted,  im- 
pressions on  the  sensory  nerves  given  off  from  it  below  the  seat  of  injury, 
cease  to  be  propagated  to  the  brain,  and  the  brain  loses  the  power  of 
voluntarily  exciting  the  motor-nerves  proceeding  from  the  portion  of 
cord  isolated  from  it.  Illustrations  of  this  are  furnished  by  various 
examples  of  paralysis,  but  by  none  better  than  by  the  common  paraplegia, 
or  loss  of  sensation  and  voluntary  motion  in  the  lower  part  of  the  body, 
in  consequence  of  destructive  disease  or  injury  of  a  portion,  including 
the  whole  thickness,  of  the  spinal  cord.  Such  lesions  destroy  the  com- 
munication between  the  brain  and  all  parts  of  the  spinal  cord  below  the 
seat  of  injury,  and  consequently  cut  off  from  their  connection  with  the 
brain  the  various  organs  supplied  with  nerves  issuing  from  those  parts  of 
the  cord. 

It  is  not  probable  that  the  conduction  of  impressions  along  the  cord 
is  effected  (to  any  great  extent),  as  was  formerly  supposed,  through  the 
gray  substance,  i.  e.,  through  the  nerve-corpuscles  and  filaments  connect- 
ing them.  All  parts  of  the  cord  are  not  alike  able  to  conduct  all  im- 
pressions; and  as  there  are  separate  nerve-fibres  for  motor  and  for  sensory 
impressions,  so  in  the  cord,  separate  and  determinate  tracts  serve  to  con_ 
duct  always  the  same  kind  of  impression. 

Experimental  and  other  observations  point  to  the  following  conclu- 

31 


482  HANDBOOK    OF    PHYSIOLOGY. 

sions  regarding  the  conduction  of  sensory  and  motor  impressions  through 
the  spinal  cord. 

It  is  important  to  bear  in  mind  that  the  gray  matter  of  the  cord,  even 
if  it  conduct  some  impressions  giving  rise  to  sensation,  appears  not  to  be 
sensitive  when  it  is  directly  stimulated.  The  explanation  probably  is, 
that  it  possesses  no  apparatus  such  as  exists  at  the  peripheral  terminations 
of  sensory  nerves,  for  the  reception  of  sensory  impressions. 


The  Conducting  Paths  in  the  Spinal  Cord. 

a.  Sensory  Impressions  are  conveyed  to  the  spinal  cord  by  the  pos- 
terior nerve-roots,  and  generally  speaking  cross  over  to  the  opposite  side, 
and  are  conveyed  upwards  in  two  or  three  paths,  according  to  the  nature 
of  the  sensory  impulse. 

(1.)  Sensibility  to  Pain  is  almost  certainly  conveyed  upwards  in  that 
part  of  the  lateral  column  which  is  called  by  Growers  the  antero-lateral 
ascending  tract  (a  l  a  t,  Fig.  333).  It  is  a  tract  of  vertical  fibres  imme- 
diately in  front  of  the  crossed  pyramidal  and  direct  cerebellar  tracts. 
The  zone  extends  across  the  lateral  column  as  a  band  which  is  largest  in 
area  near  the  periphery  of  the  cord,  where  it  fills  up  the  angle  between 
the  crossed  pyramidal  and  cerebellar  tracts,  and  it  reaches  the  surface 
of  the  cord  in  front  of  the  latter  tract;  it  then  extends  forwards  in  the 
periphery  of  the  anterior  column,  almost  to  the  anterior  median  fissure 
(G-owers). 

(2.)  Sensibility  to  Touch  (tactile  sensibility)  is  probably  conveyed  up- 
wards, after  decussating  almost  as  soon  as  it  enters  the  cord,  in  the  pos- 
terior median  column. 

(3.)  Sensibility  of  the  Muscles  (muscular  sensibility). — The  path  of 
muscular  sensation  does  not  decussate,  but  passes  upwards  probably  in 
the  posterior  median  column  of  the  same  side,  passing  up  to  it  from  the 
hinder  part  of  the  postero-external  column,  and  according  to  Flechsigin 
the  direct  cerebellar  tract. 

(4.)  Sensibility  to  Temperature. — The  path  for  sensations  of  tem- 
perature is  probably  near  to  that  of  sensibility  to  pain,  in  the  lateral 
column. 

(5.)  Sensory  Impressions  subserving  Reflex  Actions. — There  is  con- 
siderable probability  that  all  the  paths  for  cutaneous  sensibility  undergo 
interruption  in  the  spinal  cord,  and  do  not  pass  straight  up,  as  no  ascend- 
ing tract  of  degeneration  has  been  demonstrated  so  far  when  a  lesion  has 
been  confined  to  the  nerve-roots.  If  this  be  the  case,  it  is  probable  that 
the  same  fibres  which  convey  sensation  have  also  to  do  with  the  cutaneous 
reflexes.  In  the  case  of  muscular  reflexes,  however,  as  the  fibres  pass 
upwards  without  interruption,  the  reverse  is  in  all  probability  the  case, 


THE    CEREBROSPINAL    NEBV0IT8    SYSTEM. 


483 


and  special  afferent  fibres,  even  if  few  in  number,  exist,  which  are  em- 
ployed in  the  chain  of  such  reflexes. 

b.  Motor  Impressions. — Motor  impressions  are  conveyed  down- 
wards from  the  brain  along  the  pyramidal  tracts,  viz.,  the  direct  or  ante- 
rior, and  the  crossed  or  lateral,  chiefly  in  the  latter.  Generally  speaking, 
the  impressions  pass  down  on  the  side  opposite  to  which  they  originate, 
having  undergone  decussation  in  the  medulla;  but  some  impressions  do 
not  cross  in  the  medulla,  but  lower  down,  in  the  cord,  being  conveyed 
by  the  anterior  or  uncrossed  pyramidal  fibres,  and  decussate  in  the  ante- 
rior commissure.     The  motor  fibres  for  the  legs  partially  pass  downwards 


Fig.  334.— Diagram  of  the  decussation  of  the  conductors  for  voluntary  movements,  and  those 
for  sensation:  a  r,  anterior  roots  and  their  continuations  in  the  spinal  cord,  and  decussation  at  the 
lower  part  of  the  medulla  oblongata,  mo;  p  r,  the  posterior  roots  and  their  continuation  and 
decussation  in  the  spinal  cord;  g,  g,  the  ganglions  of  the  roots.  The  arrows  indicate  the  direction 
of  the  nervous  action;  r,  the  right  side;  i,  the  left  side.  1,  2,  3,  indicate  places  of  alteration  in  a 
lateral  half  of  the  spino-cerebral  axis,  to  show  the  influence  on  the  two  kinds  of  conductors,  results 
ing  from  section  of  the  cord  at  any  one  of  these  three  places.    (After  Brown-Stquard.) 

in  the  lateral  columns  of  the  same  side.  This  is  also  probably  the  case 
with  the  bilateral  muscles,  i.  e.,  muscles  of  the  two  sides  acting  together, 
such  as  the  intercostal  muscles  and  other  muscles  of  the  trunk,  as  will 
as  the  costo-humeral  muscles. 

It  is  quite  certain,  as  was  just  now  pointed  out,  that  the  fibres  of  the 
anterior  nerve-roots  are  more  numerous  than  the  fibres  proceeding  down- 
wards from  the  brain  in  the  pyramidal  tracts,  or  the  so-called  pyramidal 
fibres.  It  is  therefore  probable  that  each  pyramidal  fibre,  or  set  of  fibres, 


484  HANDBOOK   OF   PHYSIOLOGY. 

corresponds  with  an  apparatus  of  ganglion  cells  in  the  anterior  cornu 
either  on  the  same  level,  or  even  above  or  below,  that  when  this  fibre,  or 
set  of  fibres,  is  stimulated,  very  complex  co-ordinated  movements  occur 
— such  co-ordinated  movements  having  been  set  up  by  impressions  from 
a  connected  system  of  ganglion  cells,  sent  out  into  the  motor  nerve  fibres 
which  arise  from  them.  In  other  words,  it  appears  to  be  probable  that 
in  the  gray  matter  of  the  anterior  cornua  of  various  sections  of  the  cord 
are  contained  the  apparatus  for  various  complicated  co-ordinated  move- 
ments. The  apparatus  of  each  co-ordinated  movement  may  be  set  in 
motion  either  by  sensory  impressions  passing  to  the  cord,  when  the  re. 
suit  of  movement  would  be  a  reflex  action,  or  by  an  impression  travelling 
downwards  from  the  brain,  and  conveyed  by  one  or  more  pyramidal 
fibres. 

Division  of  the  anterior  pyramids  of  the  medulla  at  the  point  of  de- 
cussation (2,  Fig.  334),  is  followed  by  paralysis  of  motion,  never  quite 
absolute,  in  all  parts  below.  Disease  or  division  of  any  part  of  the  cere- 
bro-  spinal  axis  above  the  seat  of  decussation  (1,  Fig.  334)  is  followed  by 
impaired  or  lost  power  of  motion  on  the  opposite  side  of  the  body;  while 
a  like  injury  inflicted  below  this  part  (3,  Fig.  334)  induces  similar,  never 
quite  absolute  no  doubt,  on  the  corresponding  side. 

When  one  half  of  the  spinal  cord  is  cut  through,  complete  anaesthesia 
of  the  other  side  of  the  body  below  the  point  of  section  results,  but  there 
is  often  greatly  increased  sensibility  (hyperesthesia)  on  the  same  side; 
so  much  so  that  the  least  touch  appears  to  be  agonizing.  This  condition 
may  persist  for  several  days.  Similar  effects  may,  in  man,  be  the  result 
of  injury. 

In  addition  to  the  transmission  of  ordinary  sensory  and  motor  im- 
pulses, the  spinal  cord  is  the  medium  of  conduction  also  of  impulses  to 
and  from  the  Vaso-motor  centre  in  the  medulla  oblongata,  although  it 
probably  contains  special  vaso-motor  centres  of  its  own. 

It  will  be  seen  in  Chapter  XXI.  that  Gaskell  considers  that  the  white 
visceral  branches  from  the  spinal  cord  to  the  sympathetic  system  are  con- 
nected with  or  arise  from  the  posterior  vesicular  column  of  Clarke,  and 
from  the  anterior  lateral  cells.  Others  think  that  the  direct  cerebellar 
tract  arises  from  Clarke's  column. 

ransference. — Examples  of  the  transference  of  impressions  in  the 
cord  have  been  given  (p.  466);  and  that  the  transference  takes  place  in 
the  cord,  and  not  in  the  brain,  is  nearly  proved  by  the  frequent  cases  of 
pain  felt  in  the  knee  and  not  in  the  hip,  in  diseases  of  the  hip;  of  pain 
felt  in  the  urethra  or  glans  penis,  and  not  in  the  bladder,  in  calculus; 
or,  if  both  the  primary  and  the  secondary  or  transferred  impression 
were  in  the  brain,  both  should  be  felt. 


THE    CEREBROSPINAL    NEK  VOL'S    SYSTEM. 


Reflex  Action  or  Reflection. 


4>:» 


In  man  the  spinal  cord  is  so  much  under  the  control  of  the  higher 
nerve-centres,  that  its  own  individual  functions  in  relation  to  reflex  ac- 
tion are  apt  to  be  overlooked;  so  that  the  result  of  injury,  by  which  the 
cord  is  cut  off  completely  from  the  influence  of  the  encephalon,  is  apt  to 
lessen  rather  than  increase  our  estimate  of  its  importance  and  individual 
endowments.     Thus,  when  the  human  spinal  cord  is  divided,  the  lower 
extremities  fall  into  any  position  that  their  weight  and  the  resistance  of 
surrounding  objects  combine  to  give  them;  if  the  body  is  irritated,  they 
do  not  move  towards  the  irritation;  and  if  they  are  touched,  the  conse- 
quent reflex  movements  are  disorderly  and  purposeless;  all  power  of 
voluntary  movement  is  absolutely  abolished.     In  other  mammals,  how- 
ever, e.  ().,  in  the  rabbit  or  dog,  after  recovery  from  the  shock  of  the 
operation,  which  takes  some  time,  reflex  actions  in  the  parts  below  will 
occur  after  the  spinal  cord  has  been  divided,  a  very  feeble  irritation  being 
followed  by  extensive  and  co-ordinate  movements.     In  the  case  of  the 
frog,  and  many  other  cold-blooded  animals,  in  which  experimental  and 
other  injuries  of  the  nerve-tissues  are  better  borne,  and  in  which  the 
lower  nerve-centres  are  less  subordinate  in  their  action  to  the  higher,  the 
reflex  functions  of  the  cord  are  still  more  clearly  shown.     When,  for 
example,  a  frog's  head  is  cut  off,  its  limbs  remain  in,  or  assume  a  natural 
position;  they  resume  it  when  disturbed;  and  when  the  abdomen  or  back 
is  irritated,  the  feet  are  moved  with  the  manifest  purpose   of  pushing 
away  the  irritation.     The  main  difference  in  the  cold-blooded  animals 
being  that  the  reflex  movements  are  more  definite,  complicated,  and 
effective,  although  less  energetic  than  in  the  case  of  mammals.     It  might 
indeed 'be  thought,  on  superficial  examination,  that  the  mind  of  the  ani- 
mal was  engaged  in  the  acts;  and  yet  all  analogy  would  lead  us  to  the 
belief  that  the  spinal  cord  of  the  frog  has  no  different  endowment,  in 
kind,  from  those  which  belong  to  the  cord  of  the  higher  vertebrata:  the 
difference  is  only  in  degree.     And  if  this  be  granted,  it  may  be  assumed 
that,  in  man  and  the  higher  animals,  many  actions  are  performed  as  reflex 
movements  occurring  through  and  by  means  of  the  spinal  cord,  although 
the  latter  cannot  by  itself  initiate  or  even  direct  them  independently. 

Cutaneous  and  Muscle  Reflexes.— In  the  human  subject  two 
kinds  of  reflex  actions  dependent  upon  the  spinal  cord  are  usually  dis- 
tinguished, the  alterations  of  which,  either  in  the  direction  of  increase 
or  of  diminution,  are  indications  of  some  abnormality,  and  are  used  as  a 
means  of  diagnosis  in  nervous  and  other  disorders.  They  are  termed 
Tespectively  (a)  Cutaneous  reflexes,  and  (b)  Muscle  reflexes,  (a)  Cu- 
taneous reflexes  are  set  up  by  a  gentle  stimulus  applied  to  the  skin.  The 
subjacent  muscle  or  muscles  contract  in  response.  Although  these 
cutaneous  reflex  actions  may  be  demonstrated  almost  anywhere,  yet  cer- 
tain of  such  actions  as  being  most  characteristic  are  distinguished,  e.  g., 


483  HANDBOOK    OF    PHYSIOLOGY. 

plantar  reflex;  gluteal  reflex,  i.  e.,  a  contraction  of  the  gluteus  maximus 
when  the  skin  over  it  is  stimulated;  cremaster  reflex,  retraction  of  the 
testicle  when  the  skin  of  the  inside  of  the  thigh  is  stimulated,  and  the 
like.  The  ocular  reflexes,  too,  are  important.  They  are  contraction  of 
the  iris  on  exposure  to  light,  and  its  dilatation  on  stimulating  the  skin 
of  the  cervical  region.  All  of  these  cutaneous  reflexes  are  true  reflex 
actions,  but  they  differ  in  different  individuals,  and  are  more  easily 
elicited  in  the  young,  (b)  Muscle  reflexes,  or  as  they  are  often  termed, 
tendon-reflexes,  consist  of  a  contraction  of  a  muscle  under  conditions  of 
more  or  less  tension,  when  its  tendon  is  sharply  tapped.  The  so-called 
patella-tendon-reflex  is  the  most  well-known  of  this  variety  of  reflexes. 
If  one  knee  be  slightly  flexed,  as  by  crossing  it  over  the  other,  so  that 
the  quadriceps  femoris  is  extended  to  a  moderate  degree,  and  the  patella 
tendon  be  tapped  with  the  fingers  or  the  earpiece  of  a  stethoscope,  the 
muscle  contracts  and  the  knee  is  jerked  forwards. 

Another  variety  of  the  same  phenomenon  is  seen  if  the  foot  is  flexed 
so  as  to  stretch  the  calf  muscles  and  the  tendo  Achillis  is  tapped;  the 
foot  is  extended  by  the  contraction  of  the  stretched  muscles.  It  appears, 
however,  that  the  tendon  reflexes  are  not  exactly  what  their  name  im- 
plies. The  interval  between  the  tap  and  the  contraction  is  too  short  for 
the  production  of  a  true  reflex  action.  It  is  suggested  that  the  contrac- 
tion is  caused  by  local  stimulation  of  the  muscle,  but  that  this  would  not 
occur  unless  the  muscle  had  been  reflexly  stimulated  previously  by  the 
tension  applied,  and  placed  in  a  condition  of  excessive  irritability.  It  is 
further  probable  that  the  condition  on  which  it  depends  is  a  reflex  spinal 
irritability  of  the  muscle  or  (exaggerated)  muscular  tone,  which  is  ad- 
mitted to  be  a  reflex  j)henomenon. 

Inhibition  of  Reflex  Actions. — The  fact  that  such  movements  as  are 
produced  by  irritating  the  skin  of  the  lower  extremities  in  the  human 
subject,  after  division  or  disorganization  of  a  part  of  the  spinal  cord,  do 
not  follow  the  same  irritation  when  the  mind  is  active  and  connected 
with  the  cord  through  the  brain,  is,  probably,  due  to  the  mind  ordinarily 
perceiving  the  irritation  and  instantly  controlling  the  muscles  of  the 
irritated  and  other  parts;  for  even  when  the  cord  is  perfect,  such  invol- 
untary movements  will  often  follow  irritation,  if  it  be  applied  when  the 
mind  is  wholly  occupied.  When,  for  example,  one  is  anxiously  thinking, 
even  slight  stimuli  will  produce  involuntary  and  reflex  movements.  So, 
also,  during  sleep,  such  reflex  movements  may  be  observed,  when  the 
skin  is  touched  or  tickled;  for  example,  when  one  touches  with  the  finger 
the  palm  of  the  hand  of  a  sleeping  child,  the  finger  is  grasped — the  im- 
pression on  the  skin  of  the  palm  producing  a  reflex  movement  of  the 
muscles  which  close  the  hand.  But  when  the  child  is  awake,  no  such 
effect  is  produced  by  a  similar  touch. 

Further,  many  reflex  actions  are  capable  of  being  more  or  less  con- 
trolled or  even  altogether  prevented  by  the  will:  thus  an  inhibitory  ac- 
tion maybe  exercised  by  the  brain  over  reflex  functions  of  the  cord  and 
the  other  nerve  centres.  The  following  may  be  quoted  as  familiar  ex- 
amples of  this  inhibitory  action: — 


THE    CEREBROSPINAL    XERYOUS    SYSTEM.  487 

To  prevent  the  reflex  action  of  crying  out  when  in  pain,  it  is  often 
sufficient  firmly  to  clench  the  teeth  or  to  grasp  some  object  and  hold  it 
tight.  When  the  feet  are  tickled  we  can,  by  an  effort  or  will,  prevent 
the  reflex  action  of  jerking  them  up.  So,  too,  the  involuntary  closing 
of  the  eyes  and  starting,  when  a  blow  is  aimed  at  the  head,  can  be  simi- 
larly restrained. 

Darwin  has  mentioned  an  interesting  example  of  the  way  in  which, 
on  the  other  hand,  such  an  instinctive  reflex  act  may  override  the 
strongest  effort  of  the  will.  He  placed  his  face  close  against  the  glass 
of  the  cobra's  cage  in  the  Reptile  House  at  the  Zoological  Gardens,  and 
though,  of  course,  thoroughly  convinced  of  his  perfect  security,  could 
not  by  any  effort  of  the  will  prevent  himself  from  starting  back  when  the 
snake  struck  with  fury  at  the  glass. 

It  has  been  found  by  experiment  that  in  a  frog  the  optic  lobes  and 
optic  thalami  have  a  distinct  action  in  inhibiting  or  delaying  reflex  ac- 
tion, and  also  that  more  generally  any  afferent  stimulus,  if  sufficiently 
strong,  may  inhibit  or  modify  any  reflex  action  even  in  the  absence  of 
these  centres. 

On  the  Avhole,  therefore,  it  may,  from  these  and  like  facts,  be  con- 
cluded that  reflex  acts,  performed  under  the  influence  of  the  reflecting 
power  of  the  spinal  cord,  are  essentially  independent  of  the  brain  and 
may  be  performed  perfectly  when  the  brain  is  separated  from  the  cord: 
that  these  include  a  much  larger  number  of  the  natural  and  purposive 
movements  of  the  lower  animals  than  of  the  warm-blooded  auimals  and 
man:  and  that  over  nearly  all  of  them  the  mind  may  exercise,  through 
the  higher  nerve  centres,  some  control;  determining,  directing,  hinder- 
ing, or  modifying,  them,  either  by  direct  action,  or  by  its  power  over 
associated  muscles. 

To  these  instances  of  spinal  reflex  action,  some  add  yet  many  more,, 
including  nearly  all  the  acts  which  seem  to  be  performed  unconsciously, 
such  as  those  of  walking,  running,  writing,  and  the  like:  for  these  are 
really  involuntary  acts.  It  is  true  that  at  their  first  performances  they 
are  voluntary,  that  they  require  education  for  their  perfection,  and  are 
at  all  times  so  constantly  performed  in  obedience  to  a  mandate  of  the 
will,  that  it  is  difficult  to  believe  in  their  essentially  involuntary  nature. 
But  the  will  really  has  only  a  controlling  power  over  their  performance; 
it  can  hasten  or  stay  them,  but  it  has  little  or  nothing  to  do  with  the 
actual  carrying  out  of  the  effect.  And  this  is  proved  by  the  circumstance 
that  these  acts  can  be  performed  with  complete  mental  abstraction:  and, 
more  than  this,  that  the  endeavor  to  carry  them  out  entirely  by  the  ex- 
ercise of  the  Avill  is  not  only  not  beneficial,  but  positively  interferes  with 
their  harmonious  and  perfect  performance.  Any  one  may  convince  him- 
self of  this  fact  by  trying  to  take  each  step  as  a  voluntary  act  in  walking 


488  HANDBOOK    OF    PHYSIOLOGY. 

down  stairs,  or  to  form  each  letter  or  word  in  writing  by  a  distinct  exer- 
cise of  the  will. 

These  actions,  however,  will  be  again  referred  to,  when  treating  of 
their  possible  connection  with  the  functions  of  the  Sensory  Ganglia. 

Morbid  reflex  actions. — The  relation  of  the  reflex  action  to  the 
strength  of  the  stimulus  is  the  same  as  was  shown  generally  in  the  action 
of  ganglia,  a  slight  stimulus  producing  a  slight  movement,  and  a  greater. 
a  greater  movement,  and  so  on;  but  in  instances  in  which  we  must  as- 
sume that  the  cord  is  morbidly  more  irritable,  i.  e.,  apt  to  issue  more 
nervous  force  than  is  proportionate  to  the  stimulus  applied  to  it,  a  slight 
impression  on  a  sensory  nerve  produces  extensive  reflex  movements. 
This  appears  to  be  the  condition  in  tetanus,  in  which  a  slight  touch  on 
the  skin  may  throw  the  whole  body  into  convulsion.  A  similar  state  is 
induced  by  the  introduction  of  strychnia,  and,  in  frogs,  of  opium,  into 
the  blood;  and  numerous  experiments  on  frogs  thus  made  tetanic,  have 
shown  that  the  tetanus  is  wholly  unconnected  with  the  brain,  and  de- 
pends on  the  state  induced  in  the  spinal  cord. 

Special  Centres  in  Spinal  Cord. 

It  may  seem  to  have  been  implied  that  the  spinal  cord  as  a  single 
"  nerve-centre,  reflects  alike  from  all  parts  all  the  impressions  conducted 
to  it.  This,  however,  is  not  the  case,  and  it  should  be  regarded  as  we 
have  indicated,  as  a  collection  of  nervous  centres  united  in  a  continuous 
column.  This  is  well  illustrated  by  the  fact  that  segments  of  the  cord 
may  act  as  distinct  nerve-centres,  and  excite  muscular  action  in  the 
parts  supplied  with  nerves  given  off  from  them;  as  well  as  by  the  anal- 
ogy of  certain  cases  in  which  the  muscular  movements  of  single  organs 
are  under  the  control  of  certain  circumscribed  portions  of  the  cord.  The 
special  centres  are  the  following: — 

(a.)  Centre  for  Defalcation,  or  Ano- Spinal  centre. — The  mode  of  ac- 
tion of  the  ano-spinal  centre  appears  to  be  this.  The  mucous  membrane 
of  the  rectum  is  stimulated  by  the  presence  of.  faeces  or  gases  in  the 
bowel.  The  stimulus  passes  up  by  the  afferent  nerves  of  the  hsemor- 
rhoidal  and  inferior  mesenteric  plexus  to  the  centre  in  the  cord,  situated 
in  the  lumbar  enlargement,  and  is  reflected  through  the  pudendal  plexus 
to  the  anal  sphincter  on  the  one  hand,  and  on  the  other  to  the  mus- 
cular tissue  in  the  wall  of  the  lower  bowel.  In  this  way  is  produced  a 
relaxation  of  the  first  and  a  contraction  of  the  second,  and  expulsion  of 
the  contents  of  the  bowel  follows.  The  centre  in  the  spinal  cord  is  par- 
tially under  the  control  of  the  will,  so  that  its  action  may  be  either  in- 
hibited, or  augmented  or  helped.  The  action  may  be  helped,  by  the 
abdominal  muscles  which  are  under  the  control  of  the  will,  although 
under  a  strong  stimulus  they  may  also  be  compelled  to  contract  by  reflex 
action. 


THE    CEREBROSPINAL    NEBV0U8    SYS1KM.  4*9 

(b.)  Centre  for  Micturition,  or  the  Yesico- Spinal  centre. — The  vesico- 
spinal centre  acts  in  a  very  similar  way  to  that  of  the  ano-spinal.  The 
centre  is  also  in  the  lumbar  enlargement  of  the  cord.  It  may  be  stimu- 
lated to  action  by  impulses  descending  from  the  brain,  or  reflexly  by 
the  presence  of  urine  in  the  bladder.  The  action  of  the  brain  may  be 
voluntary,  or  it  may  be  excited  to  action  by  the  sensation  of  distention 
of  the  bladder  by  the  urine.  The  sensory  fibres  concerned  are  the  pos- 
terior roots  of  the  lower  sacral  nerves.  The  action  of  the  centre  thus 
stimulated  is  double,  or  it  may  be  supposed  that  the  centre  consists  of 
two  parts,  one  which  is  usually  in  action  and  maintains  the  tone  of  the 
sphincter,  and  the  other  which  causes  contraction  of  the  bladder  and 
other  muscles.  When  evacuation  of  the  bladder  is  to  occur,  impulses 
are  sent  on  the  one  hand  to  its  muscles  and  to  certain  other  muscles, 
which  cause  their  contraction,  and  on  the  other  to  the  sphincter  urethras 
which  procures  its  relaxation.  The  way  having  been  opened  by  the  re- 
laxation of  the  sphincter,  the  urine  is  expelled  by  the  combined  action 
of  the  bladder  and  accessory  muscles.  The  cerebrum  may  act  not  only 
in  the  way  of  stimulating  the  centre  to  action,  but  also  in  the  way  of  in- 
hibiting its  action.  The  abdominal  muscles  may  be  called  into  action  as 
in  defalcation. 

(c.)  Centre  for  Emission  of  Semen,  or  Genito-Spinal  centre. — The 
centre  situated  in  the  lumbar  enlargement  of  the  spinal  cord  is  stimulated 
to  action  by  sensory  impressions  from  the  glans  penis.  Efferent  im- 
pulses from  the  centre  excite  the  successive  and  co-ordinate  contractions 
of  the  muscular  fibres  of  the  vasa  deferentia  and  vesiculae  seminales,  and 
of  the  accelerator  urinae  and  other  muscles  of  the  urethra;  and  a  forcible 
expulsion  of  semen  takes  place,  over  which  the  mind  has  little  or  no  con- 
trol, and  which,  in  cases  of  paraplegia,  may  be  unfelt. 

(d.)  Centre  for  the  Erection  of  the  Penis. — This  centre  is  also  situ- 
ated in  the  lumbar  region.  It  is  excited  to  action  by  the  sensory  nerves 
of  the  penis.  Efferent  impulses  produce  dilatation  of  the  vessels  of  the 
penis,  which  also  appears  to  be  in  part  the  result  of  a  reflex  contraction 
of  the  muscles  by  which  the  veins  returning  the  blood  from  the  penis  are 
compressed. 

(e.)  Centre  for  Parturition. — The  centre  for  the  expulsion  of  the 
contents  of  the  uterus  in  parturition  is  situated  in  the  lumbar  spinal  cord 
rather  higher  up  than  the  other  centres  already  enumerated.  The  stimu- 
lation of  the  interior  of  the  uterus  by  its  contents  may,  under  certain 
conditions,  excite  the  centre  to  send  out  impulses  which  produce  a  con- 
traction of  the  uterine  walls  and  expulsion  of  the  contents  of  the  cavity. 
The  centre  is  independent  of  the  will,  since  delivery  can  take  place  in 
paraplegic  women,  and  also  whilst  a  patient  is  under  the  influence  of 
chloroform.     Again,  as  in  the  cases  of  defascation  and  micturition,  the 


490  HANDBOOK    OF    PHYSIOLOGY. 

abdominal  muscles  assist;  their  action  being  for  the  most  part  reflex  and 
involuntary. 

(/.)  Centre  for  Movements  of  Lymphatic  Hearts  of  Frog. — Volkmann 
has  shown  that  the  rhythmical  movements  of  the  anterior  pair  of  lym- 
phatic hearts  in  the  frog  depend  upon  nervous  influence  derived  from 
the  portion  of  spinal  cord  corresponding  to  the  third  vertebra,  and  those 
of  the  posterior  pair  on  influence  supplied  by  the  portion  of  cord  oppo- 
site the  eighth  vertebra.  The  movements  of  the  heart  continue,  though 
the  whole  of  the  cord,  except  the  above  portions,  be  destroyed;  but  on 
the  instant  of  destroying  either  of  these  portions,  though  all  the  rest  of 
the  cord  be  untouched,  the  movements  of  the  corresponding  hearts  cease. 
What  appears  to  be  thus  proved  in  regard  to  two  portions  of  the  cord, 
may  be  inferred  to  prevail  in  other  portions  also;  and  the  inference  is 
reconcilable  with  most  of  the  facts  known  concerning  the  physiology  and 
comparative  anatomy  of  the  cord. 

(g.)  The  Centre  for  the  Tone  of  Muscles. — The  influence  of  the  spinal 
cord  on  the  sphincter  ani  and  sphincter  urethra?  has  been  already  men- 
tioned (see  above).  It  maintains  these  muscles  in  permanent  contrac- 
tion. The  condition  of  these  sphincters,  however,  is  not  altogether  ex- 
ceptional. It  is  the  same  in  kind  though  it  exceeds  in  degree  that 
condition  of  muscles  which  has  been  called  tone,  or  passive  contraction; 
a  state  in  which  they  always  when  not  active  appear  to  be  during  health, 
and  in  which,  though  called  inactive,  they  are  in  slight  contraction,  and 
certainly  are  not  relaxed,  as  they  are  long  after  death,  or  when  the  spinal 
cord  is  destroyed.  This  tone  of  all  the  muscles  of  the  trunk  and  limbs 
depends  on  the  spinal  cord,  as  the  contraction  of  the  sphincters  does. 
If  an  animal  be  killed  by  injury  or  removal  of  the  brain,  the  tone  of  the 
muscles  may  be  felt  and  the  limbs  feel  firm  as  during  sleep;  but  if  the 
spinal  cord  be  destroyed,  the  sphincter  ani  relaxes,  and  all  the  muscles 
feel  loose,  and  flabby,  and  atonic,  and  remain  so  till  rigor  mortis  com- 
mences. 

This  kind  of  tone  must  be  distinguished  from  that  mere  firmness  and 
tension  which  it  is  customary  to  ascribe,*  under  the  name  of  tone,  to  all 
tissues  that  feel  robust  and  not  flabby,  as  well  as  to  muscles.  The  tone 
peculiar  to  muscles  has  in  it  a  degree  of  vital  contraction:  that  of  other 
tissues  is  only  due  to  their  being  well  nourished,  and  therefore  compact 
and  tense. 

All  the  foregoing  examples  illustrate  the  fact  that  the  spinal  cord  is  a 
collection  of  reflex  centres,  upon  which  the  higher  centres  act  by  sending 
down  impulses  to  set  in  motion,  modify  or  control  them.  The  move- 
ments or  other  phenomena  of  reflex  action  being  as  it  were  the  function 
of  the  ganglion  cells  to  which  an  afferent  impression  is  conveyed  by  the 
posterior  nerve-trunks  in  connection  with  them,  and  that  the  extent  of 
the  movement  depends  upon  the  strength  of  the  stimulus,  the  position 


THE    CEREBROSPINAL    NERVOUS    SYSTEM  491 

in  which  it  is  applied  as  well  as  the  condition  of  the  nerve  cells,  the  con- 
nection between  the  cells  being  so  intimate  that  a  series  of  co-ordinated 
movements  may  result  from  a  single  stimulation.  "Whether  the  cells 
possess  as  well  the  power  of  originating  impulses  (automatism)  is  doubt- 
ful, but  this  is  possible  in  the  case  of 

(h.)  Vaso-motor  centres  which  are  situated  in  the  cord  (p.  147),  and  of 

(i.)  Sweating  centres  which  must  be  closely  related  to  them,  and 
possibly  in  the  case  of 

(  /.)  The  centres  for  maintaining  the  tone  of  muscles. 

The  Nutrition  (a)  of  the  muscles,  appears  to  be  under  the  control  of 
the  spinal  cord.  "When  the  anterior  motor  nerve  cells  are  diseased  the 
muscles  atrophy.  In  the  same  way  (b)  the  bones  and  (c)  joints  are 
seriously  affected  when  the  cord  is  diseased.  The  former  where  the  an- 
terior nerve  cells  are  implicated  do  not  grow,  and  the  latter  are  disorgan- 
ized in  some  cases  when  the  posterior  columns  are  affected,  (d)  The 
skin  too  evidently  is  only  maintained  in  a  healthy  condition  as  long  as 
the  cord  and  its  nerves  are  intact.  No  doubt  part  of  this  influence 
which  the  cord  exercises  over  nutrition  is  due  to  the  relationship  which 
it  bears  to  the  vaso-motor  nerves.  "Within  the  cord  are  contained,  for 
some  distance,  fibres  (a)  which  regulate  the  dilatation  of  the  pupil,  (b) 
which  have  to  do  with  the  glycogenic  function  of  the  liver,  (c)  winch 
control  the  nerve-supply  of  the  vessels  of  the  face  and  head,  (d)  which 
produce  acceleration  of  the  heart's  action,  and,  in  fact,  all  the  other  so- 
called  sympathetic  functions  (see  Chapter  XXL). 

B.  The  Medulla  Oblongata. 

The  medulla  oblongata  (Figs.  335,  336)  is  a  column  of  gray  and 
white  nervous  substance  formed  by  the  prolongation  upwards  of  the 
spinal  cord  and  connecting  it  with  the  brain. 

Structure. — The  gray  substance  which  it  contains  is  situate'd  in  the 
interior  and  variously  divided  into  masses  and  laminae  by  the  white  or 
fibrous  substance  which  is  arranged  partly  in  external  columns,  and 
partly  in  fasciculi  traversing  the  central  gray  matter.  The  medulla  ob- 
longata is  larger  than  any  part  of  the  spinal  cord.  Its  columns  arepyri- 
form,  enlarging  as  they  proceed  towards  the  brain,  and  are  continuous 
with  those  of  the  spinal  cord.  Each  half  of  the  medulla,  therefore,  may 
be  divided  into  three  columns  or  tracts  of  fibres,  continuous  with  the 
three  tracts  of  which  each  half  of  the  spinal  cord  is  made  up.  The  col- 
umns are  more  prominent  than  those  of  the  spinal  cord,  and  separated 
from  each  other  by  deeper  grooves.  The  anterior,  continuous  with  the 
anterior  columns  of  the  cord,  are  called  the  anterior  pyramids;  the  pos- 
terior, continuous  with  the  posterior  columns  of  the  cord,  with  the  ad- 
dition of  the  funiculus  of  Rolando  on  each  side  (Fig.  337,  fl\),  are  called 


492 


HANDBOOK    OF    PHYSIOLOGY. 


the  restiform  bodies.  On  the  outer  side  of  the  anterior  pyramids  of  each 
side,  near  its  upper  part,  is  a  small  oval  mass  containing  gray  matter, 
and  named  the  olivary  body;  and  at  the  posterior  part  of  the  restiform 
column  immediately  on  each  side  of  the  posterior  median  groove,  con- 
tinuous with  the  posterior  median  column  of  the  cord,  a  small  tract  is 
marked  off  by  a  slight  groove  from  the  remainder  of  the  restiform  body, 
and  called  the  posterior  pyramid  or  fasciculus  gracilis.  The  restiform 
columns,  instead  of  remaining  parallel  with  each  other  throughout  the 
whole  length  of  the  medulla  oblongata,  diverge  near  its  upper  part, 
aud  by  thus  diverging,  lay  open,  so  to  speak,  a  space  called  the  fourth 
ventricle,  the  floor  of  which  is  formed  by  the  gray  matter  of  the  interior 
of  the  medulla,  exposed  by  this  divergence. 


''Mr 

Fig.  335. 


Fig.  336. 


Fig.  335.— Anterior  surface  of  the  pons  Varolii,  and  medulla  oblongata,  a,  a,  anterior  pyra- 
mids; b,  their  decussation;  c,  c,  olivary  bodies;  d,  d,  restiform  bodies;  e,  arciform  fibres;  /,  fibres 
passing  from  the  anterior  column  of  the  cord  to  the  cerebellum;  g.  anterior  column  of  the  spinal 
cord;  h,  lateral  column;  p,  pons  Varolii;  i,  its  upper  fibres;  5,  5,  roots  of  the  fifth  pair  of  nerves. 

Fig.  336.— Posterior  surface  of  the  pons  Varolii,  corpora  quadrigemina,  and  medulla  oblongata. 
The  peduncles  of  the  cerebellum  are  cut  short  at  the  side,  a,  a,  the  upper  pair  of  corpora  quadri- 
gemina ;  6,  6 ,  the  lower ;  /,  /,  superior  peduncles  of  the  cerebellum ;  e,  eminence  connected  with  the 
nucleus  of  the  hypoglossal  nerve ;  e,  that  of  the  glosso-pharyngeal  nerve ;  i,  that  of  the  vagus  nerve ; 
d,  d,  restiform  bodies;  p,  p,  posterior  pyramids;  v,  v,  groove  in  the  middle  of  the  fourth  ventricle, 
ending  below  in  the  calamus  scriptorius;  7,  7,  roots  of  the  auditory  nerves. 

On  separating  the  anterior  pyramids,  and  looking  into  the  groove  be- 
tween them,  some  decussating  fibres  of  the  lateral  columns  of  the  cord 
can  be  plainly  seen. 


Distribution  of  the  Fibres  of  the  Medulla  Oblongata. 

a.  The  anterior  pyramid  of  each  side,  although  mainly  composed  of 
continuations  of  the  fibres  of  the  anterior  columns  of  the  spinal  cord, 
receives  fibres  from  the  lateral  columns,  both  of  its  own  and  the  opposite 
side;  the  latter  fibres  forming  almost  entirely  the  decussating  strands 


THE    CEREBROSPINAL    NERVOUS    SYS  1  KM. 


4U3 


which  are  seen  in  the  groove  between  the  anterior  pyramids.  Thus 
composed,  the  anterior  pyramidal  fibres  proceeding  onwards  to  the  brain 
are  distributed  in  the  following  manner: — 

1.  The  greater  part  pass  on  through  the  Pons  to  the  Cerebrum.  A 
portion  of  the  fibres,  however,  running  apart  from  the  others,  joins  some 
fibres  from  the  olivary  body,  and  unites  with  them  to  form  what  is  called 
the  olivary  fasciculus  or  fillet.  2.  A  small  tract  of  fibres  proceeds  to  the 
cerebellum. 

b.  The  lateral  column  of  the  cord  on  each  side  of  the  medulla,  in 
proceeding  upwards,  divides  into  three  parts,  outer,  inner,  and  middle, 
which  are  thus  disposed  of: — 1.  The  outer  fibres  (direct  cerebellar  tract) 
go  with  the  restiform  tract  to  the  cerebellum.     2.  The  middle  (crossed 


Fig.  337.— Posterior  view  of  the  medulla,  fourth  ventricle,  and  mesencephalon  (natural  size\ 
p.n.,  line  of  the  posterior  roots  of  the  spinal  nerves;  p.m./.,  posterior  median  fissure;  f.g.,  funiculus 
gracilis;  cl.,  its  clava;  f.c,  funiculus  cuneatus;  f.R..  funiculus  of  Rolando;  r.b..  restiform  body; 
c.s.,  calamus  scriptorius;  I,  section  of  ligula  or  tseuia;  part  of  choroid  plexus  is  seen  beneath  it ; 
l.r.,  lateral  recess  of  the  ventricle;  str.,  strife  acusticae;  <'./.,  inferior  fossa;  s./.,  posterior  fossa;  be- 
tween it  and  the  median  sulcus  is  the  fasciculus  teres;  cbl.,  cut  surface  of  the  cerebellar  hemi- 
sphere; n.d..  central  or  gray  matter;  s  m  v.,  superior  medullary  velum;  big.,  ligula;  x.r.p  ,  supe- 
rior cerebellar  peduncle  cut  longitudinally;  cr„  combined  section  of  the  three  cerebellar  peduncles; 
.q.s.,  c.q.L,  corpora  quadrigemina  (superior  and  inferior);  fr.,  frtenulum;  /.,  fibres  ot  the  fillet 
een  on  the  surface  or  the  tegmentum;    c,  crusti;  l.g  ,  lateral  groove;    cg.L,  corpus  geniculum  in- 


terims; th.,  posterior  part  of  thalamus;  p.,  pineal  body, 
sponding  cranial  nerves.    (E.  A.  Schiifer.) 


The  roman  numbers  indicate  the  corre- 


pyramidal  tract)  decussate  across  the  middle  line  with  their  fellows,  and 
form  a  part  of  the  anterior  pyramid  of  the  opposite  side.  3.  The  inner 
pass  on  to  the  cerebrum,  at  first  superficially  but  afterwards  beneath 
the  olivary  body  and  the  arcuate  fibres,  and  then  proceed  along  the  floor 
of  the  fourth  ventricle,  on  each  side,  under  the  name  of  the  fasciculus 
teres. 

c.  The  posterior  column  of  the  cord  is  represented  in  the  medulla  by 


494 


HANDBOOK    OF    PHYSIOLOGY. 


i.  the  posterior  pyramid,  or  fasciculus  gracilis,  which  is  a  continuation 
of  the  posterior  median  column,  and  by  ii.  the  restiform  body,  comprising 
the  funiculus  cuneatus  and  the  funiculus  of  Rolando.  The  fasciculus 
gracilis  (Fig.  337,  f.g),  diverges  above  as  the  broader  clava  to  form  one 
on  either  side  the  lower  lateral  boundary  of  the  fourth  ventricle,  then 
tapers  off,  and  becomes  no  longer  traceable.  The  funiculus  cuneatus, 
or  the  rest  of  the  posterior  column  of  the  cord,  is  continued  up  in  the 
medulla  as  such  (Fig.  337,  f.c);  but  soon,  in  addition,  between  this  and 
the  continuation  of  the  posterior  nerve-roots,  appears  another  tract  called 
the  funiculus  of  Rolando  (Fig.  337,/. R).  High  up,  the  funiculus  cune- 
atus is  covered  by  a  set  of  fibres  (arcuate  fibres),  which  issue  from  the 
anterior  median  fissure,  turn  upwards  over  the  anterior  pyramids  to  pass 
directly  into  the  corresponding  hemisphere  of  the  cerebellum,  being 
joined  by  the  fibres  of  the  direct  cerebellar  tract;  the  funiculus  of 


p.w,/.   fa   -n.g      fc_ 


n32 


Fig.  338.— Section  of  the  medulla  oblongata  in  the  region  of  the  superior  pyramidal  decussation; 
a.m.f.,  anterior  median  fissure;  fa.,  superficial  arciform  fibres  emeraring  from  the  fissure;  py., 
pyramid;  n.a.r.,  nuclei  of  arciform  fibres;  f.a.,  deep  arciform  becoming  superficial;  o.,  lower  end 
of  olivary  nucleus;  n.l.,  nucleus  lateralis;  f.r.,  formatio  reticularis;  f.aM,  arciform  fibres  proceeding 
from  the  formatio  reticularis;  g.,  substantia  gelatinosa  of  Rolando;  a.V.,  ascending  root  of  fifth 
nerve;  n.c,  nucleus  cuneatus;  n.c'.,  external  cuneate  nucleus;  n.g.,  nucleus  gracilis;  f.g.,  funiculus 
gracilis;  p.m.f.,  posterior  median  fissure;  c.c,  central  canal  surrounded  by  gray  matter,  in  which 
are  n.XL,  nucleus  of  the  spinal  accessory,  and  n.XIL,  nucleus  of  the  hypogiossal;  s.d..  superior 
pyramidal  decussation.    (Modified  from  Schwalbe.) 

Fig.  339.— Section  of  the  medulla  oblongata  at  about  the  middle  of  the  olivary  body,  f.l.a.,  ante- 
rior median  fissure;  n.ar.,  nucleus  arciformis;  p.,  pyramid;  XII.,  bundle  of  hypoglossal  nerve 
emerging  from  the  surface;  at  b,  it  is  seen  coursing  between  the  pyramid  and  the  olivary  nucleus,  o. ; 
f.a.e.,  external  arciform  fibres;  n.l ,  nucleus  lateralis;  a.,  arciform  fibres  passing  towards  restiform 
body,  partly  through  the  substantia  gelatinosa,  g.,  partly  superficial  to  the  ascending  root  of  the 
fifth  nerve,  a.  V.;  X.,  bundle  of  vagus  root  emerging ;  f.r  ,  formatio  reticularis ;  c.r.,  corpus  resti- 
forme,  beginning  to  be  formed,  chiefly  by  arciform  fibres,  superficial  and  deep;  n.c,  nucleus  cune- 
atus; n.g.,  nucleus  gracilis;  t.,  attachment  of  the  ligula;  f.s.,  funiculus  solitarius;  n.X .  n.X'.,  two 
parts  of  the  vagus  nucleus;  n.XIL,  hypoglossal  nucleus;  n.t.,  nucleus  of  the  funiculus  teres;  n.am., 
nucleus  ambiguus;  r.,  raphe;  A.,  continuation  of  the  anterior  column  of  cord;  o',  o",  accessory 
olivary  nucleus;  p.o.,  pedunculus  olivse.    CModified  from  Schwaibe.) 


Rolando,  and  the  funiculus  cuneatus,  although  appearing  to  join  them, 
do  not  actually  do  so,  except  to  a  partial  extent. 


THE    CEREBRO-SPINAL    NERVOUS    SYSTEM.  495 

Gray  Matter  of  the  Medulla. — To  a  considerable  extent  the  gray  mat- 
ter of  the  medulla  is  a  continuation  of  that  in  the  spinal  cord,  but  the 
arrangement  is  somewhat  different. 

The  displacement  of  the  anterior  cornu  takes  place  because  of  the 
decussation  of  a  large  part  of  the  fibres  of  the  lateral  columns  in  the 
anterior  pyramids  passing  through  the  gray  matter  of  the  anterior 
cornu,  so  that  the  caput  cornu  is  cut  off  from  the  rest  of  the  gray 
matter,  and  is,  moreover,  pushed  backwards  by  the  olivary  body,  to  be 
mentioned  below.  It  lies  in  the  lateral  portion  of  the  medulla,  and  ex- 
ists for  a  time  as  the  nucleus  lateralis  (Fig.  338,  nl);  it  consists  of  a  retic- 
ulum of  gray  matter,  containing  ganglion  cells  intersected  by  white 
nerve-fibres.  The  base  of  the  anterior  cornu  is  pushed  more  from  the 
anterior  surface,  and  when  the  central  canal  opens  out  into  the  fourth 
ventricle,  forms  a  collection  of  ganglion  cells,  producing  the  eminence 
of  the  fasciculus  teres;  from  certain  large  cells  in  it  arise  the  hypoglossal 
nerve  (Fig.  338,  XII.),  which  passes  through  the  medulla,  and  appears 
between  the  olivary  body  and  the  anterior  pyramids. 

In  the  fasciculus  teres,  nearer  to  the  middle  line  as  well  as  to  the  sur- 
face, is  a  collection  of  nerve  cells  called  the  nucleus  of  that  funiculus 
(Fig.  339,  nt).  The  gray  matter  of  the  posterior  cornu  is  displaced 
somewhat  by  bands  of  fibres  passing  through  it.  The  caput  cornu  ap- 
pears at  the  surface  as  the  funiculus  of  Eolando,  whilst  the  cervix  cornu 
is  broken  up  into  a  reticulated  structure  which  is  displaced  laterally, 
similar  in  structure  to  the  nucleus  lateralis.  From  the  increase  of  the 
base  of  the  posterior  cornu,  the  nuclei  of  the  funiculus  gracilis  and  fu- 
niculus cuneatus  are  derived  (Fig.  339,  n.g,  n.c),  and  outside  of  the  latter 
is  an  accessory  nucleus  formed  (Fig.  339,  n.c).  Internally  to  these  latter, 
and  also  derived  from  the  cells  of  the  base  of  the  posterior  cornu  and  ap- 
pearing in  the  floor  of  the  fourth  ventricle,  when  the  central  canal  opens 
are  the  nuclei  of  the  spinal  accessory,  vagus,  and  glossopharyngeal 
nerves.  In  the  upper  part  of  the  medulla  also,  to  the  outside  of  these 
three  nuclei,  is  found  the  principal  auditory  nucleus.  All  the  above 
nuclei  appear  to  be  derived  from  a  continuation  of  the  gray  matter  of 
the  spinal  cord,  but  a  fresh  collection  of  gray  matter  not  represented  is 
interpolated  between  the  anterior  pyramids  and  the  lateral  column,  con- 
tained within  the  olivary  prominence,  the  wavy  line  of  which  (corpus 
dentatum)  is  doubled  upon  itself  at  an  angle  with  the  extremities 
directed  upwards  and  inwards  (Fig.  339,  o).  There  may  also  be  a  smaller 
collection  of  gray  matter  on  the  outer  and  inner  side  of  the  olivary  nu- 
cleus known  as  accessory  olivary  nuclei. 

Functions. — As  in  case  of  the  spinal  cord,  the  functions  of  the  me- 
dulla oblongata,  like  those  of  the  spinal  cord,  may  be  considered  under 
the  heads  of: — 1.  Conduction;  2.  Reflex  action,  or  Reflection;  and,  in 
addition,  3.  Automatism. 

1.  In  conducting  impressions  the  medulla  oblongata  has  a  wider  ex- 
tent of  function  than  any  other  part  of  the  nervous  system,  since  it  is 
obvious  that  all  impressions  passing  to  and  fro  between  the  brain  and 
the  spinal  cord  and  all  nerves  arising  below  the  pons,  must  be  transmitted 
through  it. 


-196  HANDBOOK    OF  PHYSIOLOGY. 

2.  As  a  nerve-centre  by  which  impressions  are  reflected,  the  medulla 
oblongata  also  resembles  the  spinal  cord;  the  only  difference  between 
them  consisting  of  the  fact  that  many  of  the  reflex  actions  performed  by 
the  former  are  much  more  important  to  life  than  any  performed  by  the 
spinal  cord. 

Demonstration  of  Functions. — It  has  been  proved  by  repeated  experi- 
ments on  the  lower  animals  that  the  entire  brain  may  be  gradually  cut 
away  in  successive  portions,  and  yet  life  may  continue  for  a  considerable 
time,  and  the  respiratory  movements  be  uninterrupted.  Life  may  also 
continue  when  the  spinal  cord  is  cut  away  in  successive  portions  from 
below  upwards  as  high  as  tbe  point  of  origin  of  the  phrenic  nerve.  In 
Amphibia,  the  brain  has  been  all  removed  from  above,  and  the  cord,  as 
far  as  the  medulla  oblongata,  from  below;  and  so  long  as  the  medulla 
oblongata  was  intact,  respiration  and  life  were  maintained.  But  if.  in 
any  animal,  the  medulla  oblongata  is  wounded, particularly  if  it  is  wounded 
in  its  central  part,  opposite  the  origin  of  the  pneumogastric  nerves,  the 
respiratory  movements  cease,  and  the  animal  dies  asphyxiated.  And  this 
effect  ensues  even  when  all  parts  of  the  nervous  system,  except  the 
medulla  oblongata,  are  left  intact 

Injury  and  disease  in  men  prove  the  same  as  these  experiments  on 
animals.  Numerous  instances  are  recorded  in  which  injury  to  the 
medulla  oblongata  has  produced  instantaneous  death;  and,  indeed,  it  is 
through  injury  of  it,  or  of  the  part  of  the  cord  connecting  it  with  the 
origin  of  the  phrenic  nerve,  that  death  is  commonly  produced  in  frac- 
tures attended  by  sudden  displacement  of  the  upper  cervical  vertebras. 

Special  Centres. 

In  the  medulla  are  contained  a  considerable  number  of  centres  which 
preside  over  many  important  and  complicated  co-ordinated  movements 
of  muscles.  The  majority  of  these  centres  are  (a.)  reflex  centres  sim- 
ply, which  are  stimulated  by  afferent  or  by  voluntary  impressions. 
Some  of  them  are  (b.)  automatic  centres,  being  capable  of  sending 
out  efferent  impulses,  generally  rhythmical,  without  previous  stimu- 
lation by  afferent  or  by  voluntary  impressions.  The  automatic  centres 
are,  however,  generally  influenced  by  reflex  or  by  voluntary  impulses* 
Some  again  of  the  centres,  whether  reflex  or  automatic,  are  (c.)  control 
centres,  by  which  subsidiary  spinal  centres  are  governed.  Finally  the 
action  of  some  of  the  centres  is  (d.)  tonic,  i.  e.,  they  exercise  their  influ- 
ence, either  directly  or  through  another  apparatus,  continuously  and 
uninterruptedly  in  maintaining  a  regular  action. 

(a.)  Simple  Reflex  centres, 

(1.)  A  centre  for  the  co-ordinated  movements  of  Mastication,  the 
afferent  and  efferent  nerves  of  which  have  been  already  enumerated  (p. 
230). 


THE    CEREBRO-SPIXAE    NERVOUS    SYSTEM.  497 

(2.)  A  centre  for  the  movements  of  Deglutition.  The  medulla  ob- 
longata appears  to  contain  the  centre  whence  are  derived  the  motor 
impulses  enabling  the  muscles  of  the  palate,  pharynx,  and  oesophagus  to 
produce  the  successive  co  ordinate  and  adapted  movements  necessary  to 
the  act  of  deglutition  (p.  245).  This  is  proved  by  the  persistence  of 
swallowing  in  some  of  the  lower  animals  after  destruction  of  the  cerebral 
hemispheres  and  cerebellum;  its  existence  in  anencephalous  monsters; 
the  power  of  swallowing  possessed  by  the  marsupial  embryo  before  the 
brain  is  developed;  and  by  the  complete  arrest  of  the  power  of  swallow- 
ing when  the  medulla  oblongata  is  injured  in  experiments. 

(3.)  A  centre  for  the  combined  muscular  movements  of  Slicking,  the 
motor  nerves  concerned  being  the  facial  for  the  lips  and  mouth,  the 
hypoglossal  for  the  tongue,  and  the  inferior  maxillary  division  of  the  5th 
for  the  muscles  of  the  jaw. 

(4.)  A  centre  for  the  Secretion  of  Saliva,  which  has  been  already 
mentioned  (p.  237). 

(5.)  A  centre  for  Vomiting  (p.  258). 

(6.)  A  centre  for  Coughing,  which  is  said  to  be  independent  of  the 

respiratory  centre,  being   situated   above   the   inspiratory  part  of  that 

centre. 

(7.)  A  centre  for  Sneezing,  connected  no  doubt  with  the  respiratory 

centre. 

(8.)  A  centre  for  the  Dilatation  of  the  pupil,  the  fibres  from  which 
pass  out  partly  in  the  third  nerve  and  partly  through  the  spinal  cord 
(through  the  last  two  cervical  and  two  upper  dorsal  nerves?)  into  the 
cervical  sympathetic. 

(b  )  Automatic  centres. 

(1.)  Respiratory  centre. — The  action  of  the  respiratory  centre  has 
been  already  discussed.  It  is  only  necessary  to  repeat  here  that  although 
it  can  be  influenced  by  afferent  impulses,  it  is  also  automatic  in  its 
action,  being  capable  of  direct  stimulation,  as  by  the  condition  of  the 
blood  circulating  within  it.  It  is  also  bilateral.  It  probably  consists  of 
an  inspiratory  part  and  of  an  expiratory  part.  The  centre  is  capable  of 
being  influenced  both  reflexly  and  to  a  certain  extent  also  by  voluntary 
impulses.  The  vagus  influence  is  probably  constant  in  the  direction  of 
stimulating  the  inspiratory  portion  of  the  centre,  whereas  the  influence 
of  the  superior  laryngeal  is  not  always  in  action,  and  is  inhibitory. 

(2.)  The  Gardio-Inhibitory  centre.  The  action  of  this  centre  in 
maintaining  the  proper  rhythm  of  the  heart  through  the  vagus  fibres, 
which  terminate  in  a  local  intrinsic  mechanism,  has  been  already  dis- 
cussed. The  centre  can  be  directly  stimulated,  as  by  the  condition  of 
the  blood  circulating  within  it,  and  also  iudirectly  by  afferent  stimuli, 
especially  by  stimulating  the  abdominal  sympathetic  nerves,  but  also  by 
stimulating  anv  sensorv  nerve,  including  the  vagus  itself. 
32' 


498  HANDBOOK    OF    PHYSIOLOGY. 

(3.)  The  Accelerator  centre  for  the  heart.  A  centre  from  which  arise 
the  accelerator  fihres  of  the  heart,  probably  exists  in  the  medulla.  It  is 
automatic  but  not  tonic  in  action. 

(4.)  The  Vaso-motor  centre,  which  controls  the  unstripecl  muscle  of 
the  arteries,  is  also  situated  in  the  medulla.  Like  the  respiratory  centre, 
it  is  bilateral. 

As  has  already  been  pointed  out,  this  centre  may  be  directly  or  re- 
flexly  stimulated,  as  well  as  by  impressions  conveyed  downwards  from 
the  cerebrum  to  the  medulla.  The  condition  of  the  blood  circulating  in 
it  is  the  direct  stimulus.  Its  influence  is  no  doubt  a  tonic  or  else  a 
rhythmic  one.  It  is  also  supposed  that  there  is  in  the  medulla  a  special 
vaso-dilator  centre,  not  acting  tonically,  stimulation  of  which  produces 
vascular  dilatation.  The  diabetic  centre  is  probably  a  part  of  the  vaso- 
motor centre,  at  any  rate  stimulation  of  it  causes  dilatation  of  the  vessels 
of  the  liver. 

(5.)  A  chief  centre  for  the  secretion  of  Stveat  exists  in  the  medulla. 
It  controls  the  subsidiary  spinal  sweat  centres.  It  is  double,  and  the  two 
sides  may  be  excited  unequally  so  as  to  produce  unilateral  sweating.  It 
is  probably  automatic  and  reflex. 

(6.)  A  Spasm  centre  is  said  to  be  present  in  the  medulla,  on  the 
stimulation  of  which,  as  by  suddenly  produced  excessive  venosity  of 
the  blood,  general  spasms  of  the  muscles  of  the  body  are  produced. 

(c.)  Control  centres.  These  are  centres  whose  influence  maybe 
directed  to  controlling  the  action  of  the  subsidiary  centres.     They  are — 

(1.)  The  Respiratory  centre,  which  probably  controls  the  action  of 
other  subordinate  centres  in  the  spinal  cord. 

(2.)  The  Cardio-InMMtory,  which  acts  upon  a  local  ganglionic 
mechanism  in  the  heart. 

(3.)  The  Accelerator  centre,  if  it  exists,  probably  acts  through  a  local 
mechanism  in  the  heart. 

(4.)  The  Vaso-motor  centre  controls  spinal  as  well  as  local  tonic 
centres. 

(5.)  The  medullary  Sweat  centre  controls  spinal  sweat  centres. 

(d.)  Tonic  centres.  Of  the  centres  whose  action  is  tonic  or  con- 
tinuous up  to  a  certain  degree,  may  be  cited  the  vaso-motor  and  the 
cardio-inhibitory . 

It  should  not  be  forgotten  that  in  the  medulla  are  the  centres  for  the 
special  senses,  Hearing  and  Taste,  and  that  other  special  centres  are 
supposed  to  be  localized  there,  of  which  may  be  mentioned  one,  the 
hypothetical  Inhibitory  heat  centre,  which  controls  the  production  of 
heat  by  the  tissues,  independently  of  the  vaso-motor  centre. 

Though  respiration  and  life  continue  while  the  medulla  oblongata  is 
perfect  and  in  connection  with  the  respiratory  nerves,  yet,  when  all  the 
brain  above  it  is  removed,  there  is  no  more  appearance  of  sensation,  or 


THE    CKREBRO-8PINAL    NERVOUS    SYSTEM.  49.) 

•will,  or  of  any  mental  act  in  the  animal,  the  subject  of  the  experiment, 
than  there  is  when  only  the  spinal  cord  is  left.  The  movements  are  all 
involuntary  and  unfelt;  and  the  medulla  oblongata  has,  therefore,  no 
claim  to  be  considered  as  an  organ  of  the  mind,  or  as  the  seat  of  sensa- 
tion or  voluntary  poiuer.  These  are  connected  with  parts  to  be  after- 
wards described. 

C.  The  Pons  Varolii. 

Structure. — The  meso-cephalon,  or  pons  Varolii  (vi.,  Fig.  341),  is 
composed  principally  of  transverse  fibres  connecting  the  two  hemispheres 
of  the  cerebellum,  and  forming  its  principal  transverse  commissure. 
But  it  includes,  interlacing  with  these,  numerous  longitudinal  fibres 
which  connect  the  medulla  oblongata  with  the  cerebrum,  and  transverse 
fibres  which  connect  it  with  the  cerebellum.  Among  the  fasciculi  of 
nerve-fibres  by  which  these  several  parts  are  connected,  the  pons  also 
contains  abundant  gray  or  vesicular  substance,  which  appears  irregularly 
placed  among  the  fibres,  and  fills  up  all  the  interstices.  The  fibres  of 
the  facial  nerve  probably  decussate  in  the  pons. 

Functions. — The  anatomical  distribution  of  the  fibres,  both  transverse 
and  longitudinal,  of  which  the  pons  is  composed,  is  sufficient  evidence 
of  its  functions  as  a  conductor  of  impressions  from  one  part  of  the 
cerebro-spinal  axis  to  another.  Concerning  its  functions  as  a  nerve- 
centre,  little  or  nothing  is  certainly  known. 

An  important  point  in  the  diagnosis  of  lesions  of  the  pons  Varolii  is 
the  occurrence  of  a  variety  of  what  is  called  crossed  paralysis.  If  the 
lesion  be  in  the  lower  half  of  the  pons,  there  is  paralysis,  motor  and  sen- 
sory, more  or  less  complete  of  the  opposite  side  of  the  body,  with 
paralysis  of  the  facial  nerve  of  the  same  side.  If  the  lesion  be  in  the 
upper  half  of  the  pons,  the  facial  nerve  is  paralyzed  on  the  same  side  as 
the  other  paralysis,  but  other  nerves  are  involved.  Hyperpyrexia  follows 
after  some  lesions  of  the  pons. 

D.  The  Crura  Cerebri. 

Structure. — The  Crura  Cerebri  (in.,  Fig.  341)  are  principally  formed 
of  nerve-fibres,  of  which  the  inferior  or  more  superficial  (crusta)  are  in 
part  continuous  with  those  of  the  anterior  pyramidal  tracts  of  the  medulla 
oblongata,  and  the  superior  or  deeper  fibres  (tegmentum)  with  the 
lateral  and  posterior  pyramidal  tracts,  and  with  the  olivary  fasciculus. 
The  middle  third  only  of  the  crusta  contains  the  fibres  of  the  pyra- 
midal tracts.  The  outer  third  transmits  fibres  which  connect  the  cere- 
bellum with  the  temporal  and  occipital  lobes,  and  the  inner  third  fibres 
which  connect  the  frontal  lobes  -with  the  cerebellum  through  its  superior 
peduncles. 


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Each  cms  cerebri  contains  among  its  fibres  a  mass  of  gray  substance,. 
the  locus  niger. 

Functions. — With  regard  to  their  functions,  the  crura  cerebri  may  be 
regarded  as,  principally,  conducting  organs:  the  crusta  conducting 
chiefly  motor  and  the  tegmentum  sensory  impressions.  As  nerve-centres 
they  are  probably  connected  with  the  functions  of  the  third  cerebral 
nerve,  which  arises  from  the  locus  niger,  and  through  which  are  directed 
the  chief  of  the  numerous  and  complicated  movements  of  the  eyeball. 
The  crura  cerebri  are  also  in  all  probability  connected  with  the  co-ordi- 
nation of  other  movements  besides  those  of  the  eye,  as  either  rotatory 
or  disorderly  movements  result  after  section  of  either  of  them. 

Lesion  of  one  crus  is  followed  by  motor  and  sensory,  partial  or  com- 


Fig.  340.— Diagram  of  the  motor  tract  as  shown  in  a  diagrammatic  horizontal  section  through  the 
Cerebral  hemispheres,  Crura,  Pons,  and  Medulla.  Fr.,  frontal  lobe;  Oc,  occipital  lobe;  AF.,  ascend- 
ing frontal;  AP.,  ascending  parietal,  convolutions;  pCf.,  pre-central  Assure  in  front  of  the  ascend- 
ing frontal  convolution;  FR.,  fissure  of  Rolando;  IPF  ,  inter-parietal  fissure,  a  section  of  crus  is  let- 
tered on  the  left  side.  SN. ,  substantia  nigra ;  Py.,  pyramidal  motor  fibre,  which  on  the  right  is  shown 
as  continuous  lines  converging  to  pass  through  the  posterior  limb  of  IO,  internal  capsule  (the  knee 
or  elbow  of  which  is  shown  thus  *)  upwards  into  the  hemisphere  and  downwards  through  the  pons 
to  cross  the  medulla  in  the  anterior  pyramids.    (Gowers.) 

plete  paralysis  of  the  opposite  side  of  the  body  and  paralysis  of  the  third 
nerve  of  the  same  side  as  the  lesion. 


E.  The  Corpora  Quadrigemina. 

The  corpora  quadrigemina  (from  which,  in  function,  the  corpora 
geniculata  are  not  distinguishable)  are  the  homologues  of  the  optic  lobes 
in  Birds,  Amphibia,  and  Fishes,  and  may  be  regarded  as  the  principal 
nerve-centres  for  visual  sensations. 

Functions. — (1)  The  experiments  of  Flourens,  Longet,  and  Hertwig 
show  that  removal  of  the  corpora  quadrigemina  loliolly  destroys  the  power 


THE    CEREBROSPINAL    NEBVOTJS    SYSTEM. 


501 


of  seeing;  and  diseases  in  which  they  are  disorganized  are  usually  accom- 
panied by  blindness.  Atrophy  of  them  is  also  often  a  consequence  of 
atrophy  of  the  eyes.  Destruction  of  one  of  the  corpora  quadrigemina 
(or  of  one  optic  lobe  in  birds)  produces  blindness  of  the  opposite  eye. 
This  loss  of  sight  is  the  only  apparent  injury  of  sensibility  sustained  by 
the  removal  of  the  corpora  quadrigemina. 

The  (2)  removal  of  one  of  them  affects  the  movements  of  the  body,  so 
that  animals  rotate,  as  after  division  of  the  crus  cerebri,  only  more 
slowly:  but  this  may  be  due  to  giddiness  and  partial  loss  of  sight. 

(3)  The  more  evident  and  direct  influence  is  that  yjroduced  on  the  iris. 
It  contracts  when  the  corpora  quadrigemina  are  irritated:  it  is  always 


Fig.  341.— Base  of  the  brain.  1,  superior  longitudinal  fissure;  2,  2',  3",  anterior  cerebral  lobe;  3, 
fissure  of  Sylvius,  between  anterior  and  4,  4',  4",  middle  cerebral  lobe;  5,5',  posterior  lobe;  •>, 
medulla  oblongata;  the  figure  Si  in  the  right  anterior  pyramid;  7,  8,  9.  10,  the  cerebellum;  +  the  in- 
ferior vermiform  process.  The  figures  from  I.  to  IX.  are  placed  against  the  corresponding  cerebral 
nerves;  in.  is  placed  on  the  right  crus  cerebri.  VI.  and  VII.  on  the  pons  Varolii ;  X.  the  lirst  cervi- 
cal or  suboccipital  nerve.    (Allen  Thomson.)    X. 


dilated  when  they  are  removed:  so  that  they  may  be  regarded,  in  some 
measure  at  least,  as  the  nervous  centres  governing  its  movements,  and 
adapting  them  to  the  impressions  derived  from  the  retina  through  the 
optic  nerves  and  tracts. 

(4)  The  centre  for  the  co-ordination  of  the  movements  of  the  eyes  is 
also  contained  in  them.  This  centre  is  closely  associated  with  that  for 
contraction  of  the  pupil,  and  so  it  follows  that  contraction  or  dilatation 
follows  upon  certain  definite  ocular  movements. 


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F.  The  Cerebrum. 

Relation  to  other  parts. — The  relation  of  the  cerebrum  to  the  other 
parts  of  the  central  nervous  system  will  be  understood  on  reference  to 
Figs.  343,  344. 

It  is  composed  of  two  so-called  halves  or  hemispheres,  and  is  placed  in 
connection  with  the  Pons  and  Medulla  oblongata  by  its  two  Crura  or  pe- 
duncles (III.  Fig.  341):  it  is  connected  with  the  cerebellum  by  the  pro- 
cesses called  superior  crura  of  the  cerebellum,  ox  processus  a  cerebello  ad 
testes,  and  by  a  layer  of  gray  matter,  called  the  valve  of  Vieussens.  which. 


Fig.  342.— Dissection  of  brain,  from  above,  exposing  the  lateral  fourth  and  fifth  ventricles  with 
the  surrounding  parts.  X.— a,  anterior  part,  or  genu  of  corpus  callosum ;  b,  corpus  striatum;  6', 
the  corpus  striatum  of  left  side,  dissected  so  as  to  expose  its  pray  substance;  c,  points  by  a  line  to 
the  taenia  semicircularis ;  d,  optic  thalamus;  e,  anterior  pillars  of  fornix  divided;  below  they  are 
seen  descending  in  front  of  the  third  ventricle  and  between  them  is  seen  part  of  the  anterior  com- 
missure; in  front  of  the  letter  e  is  seen  the  slit-like  fifth  ventricle,  between  the  two  laminae  of  the 
septum  lucidum;  /,  soft  or  middle  commissure;  g  is  placed  in  the  posterior  part  of  the  third  ven- 
tricle; immediately  behind  the  latter  are  the  posterior  commissure  ("just  visible)  and  the  pineal  gland, 
the  two  crura  of  which  extend  forwards  along  the  inner  and  upper  margins  of  the  optic  thalami; 
Tiand  i.  the  corpora  quadrigemina;  fc,  superior  cms  of  cerebellum,  close  to  k  is  the  valve  of  Vieus- 
sens, which  has  been  divided  so  as  to  expose  the  fourth  ventricle;  I,  hippocampus  major  and  cor- 
pus fimbriatum,  or  taenia  hippocampi;  m,  hippocampus  minor;  n,  emiuentia  collateralis;  o,  fourth 
ventricle;  p,  posterior  surface  of  medulla  oblongata;  r,  section  of  cerebellum;  s,  upper  part  of  left 
hemisphere  of  cerebellum  exposed  by  the  removal  of  part  of  the  posterior  cerebral  lobe. 
(Hirschfeld  and  Leveillc.) 
I 

lies  between  these  processes,  and  extends  from  the  inferior  vermiform 
process  of  the  cerebellum  to  the  corpora  quadrigemina  of  the  cerebrum. 
These  parts,  which  thus  connect  the  cerebrum  with  the  other  principal 
divisions  of  the  cerebro-spinal  system,  may,  therefore,  be  regarded  as  the 


THE   CEREBROSPINAL    NERVOUS    SYSTEM. 


5<B 


continuation  of  the  cerebro-spinal  axis  or  column;  on  which,  as  a  kind 
of  offset  from  the  main  nerve-path,  the  cerebellum  is  placed;  and  on  the 
further  continuation  of  which  in  the  direct  line,  is  placed  the  cerebrum 
(Fig.  343). 

When  the  two  hemispheres  are  separated  and  turned  to  either  side,  a 
broad  connecting  band  or  commissure,  the  corpus  callosum,  is  seen. 

Convolutions  of  the  Cerebrum.— For  convenience  of  description, 
the  surface  of  the  brain  has  been  divided  intone  lobes  (Gratiolet). 

1.  Frontal  (F.  Figs.  343,  344),  limited  behind  by  the  fissure  of  Ro- 
lando (central  fissure),  and  beneath  by  the  fissure  of  Sylvius.  Its  surface 
consists  of  three  main  convolutions,  which  are  approximately  horizontal 
in  direction,  and  are  broken  up  into  numerous  secondary  gyri.  They 
are  termed  the  superior,  middle,  and  inferior  frontal  convolutions.     In 


Fig.  343.— Plan  in  outline  of  the  encephalon,  as  seen  from  the  right  side.  X.  The  parts  are 
represented  as  separated  from  one  another  somewhat  more  than  natural,  so  as  to  show  their  con- 
nections. A,  cerebrum;  /,  g,  h,  its  anterior,  middle,  and  posterior  lobes;  e,  fissure  of  Sylvius;  B, 
cerebellum;  C,  pons  Varolii;  D,  medulla  oblongata;  a,  peduncles  of  the  cerebrum;  b,  c,  d,  superior, 
middle,  and  inferior  peduncles  of  the  cerebellum.    (From  Quain.) 

addition,  the  frontal  lobe  contains,  at  its  posterior  part,  a  convolution 
which  runs  upwards  almost  vertically  ("ascending  frontal"),  and  is 
bounded  in  front  by  a  fissure  termed  the  praecentral,  behind  by  that  of 
Rolando. 

2.  Parietal  (P.).  This  lobe  is  bounded  in  front  by  the  fissure  of 
Rolando,  behind  by  the  external  perpendicular  fissure  (parietooccipital), 
and  below  by  the  fissure  of  Sylvius.  Behind  the  fissure  of  Rolando  is 
the  "  ascending  parietal  "  convolution,  which  swells  out  at  its  upper  end 
into  what  is  termed  the  superior  parietal  lobule.  The  superior  parietal 
lobule  is  separated  from  the  inferior  parietal  lobule  by  the  intra-parietal 
sulcus.  The  inferior  parietal  lobule  (pli  conrbe)  is  situated  at  the  pos- 
terior and  upper  end  of  the  fissure  of  Sylvius;  it  consists  of  (a)  an  ante- 
rior part  (supra-marginal   convolution)  which  hooks  round  the  end   of 


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the  fissure  of  Sylvius,  and  joins  the  superior  temporal  convolution,  and 
a  posterior  part  (b)  (angular  gyrus)  which  hooks  round  into  the  middle 
temporal  convolution. 

3.  Tempo?'0-sphenoidal  (T.),  contains  three  well-marked  convolutions, 
parallel  to  each  other,  termed  the  superior,  middle,  and  inferior  temporal. 
The  superior  and  middle  are  separated  by  the  parallel  fissure. 

4.  Occipital  (0.).  This  lobe  lies  behind  the  external  perpendicular 
or  parieto-occipital  fissure,  and  contains  three  convolutions,  termed  the 
superior,  middle,  and  inferior  occipital.  They  are  often  not  well 
marked.  In  man,  the  external  parieto-occipital  fissure  is  only  to  be  dis- 
tinguished as  a  notch  in  the  inner  edge  of  the  hemisphere;  below  this  it 
is  quite  obliterated  by  the  four  annectent  gyri  (plis  de  passage)  which 


Fig.  341.— Lateral  view  of  the  brain  f  semi-diagrammatic).  F,  Frontal  lobe;  P,  Parietal  lobe;  O,  Oc- 
cipital lobe;  T,  Temporo-sphenoidal  lobe;  S,  Assure  of  Sylvius;  S'.  horizontal,  S",  ascending  ramus 
of  the  same,  c,  sulcus  centralis  (fissure  of  Rolando);  A,  ascending  frontal;  B,  ascending  parietal 
convolution;  Fl,  superior;  F2,  middle;  F3,  inferior  frontal  convolutions;  fl,  superior.  f2,  inferior 
frontal  sulcus;  f 3,  prsecentral  sulcus;  PI.  superior  parietal  lobule;  P2,  inferior  parietal  lobule  con- 
sisting of  P2,  supramarginal  gyrus,  and  P2',  angular  gyrus;  ip,  interparietal  sulcus;  cm,  termination 
of  callosa-marginal  fissure;  01,  first.  02,  second,  03,  third  occipital  convolutions;  po,  parieto-occip- 
ital fissure;  o,  transverse  occipital  fissure;  o2,  sulcus  occipitalis  inferior;  Tl,  first,  T2,  second,  T3, 
third  temporo-sphenoidal  convolutions;  tl,  first,  t2,  second  temporo-sphenoidal  fissures.    (Ecker.) 

run  nearly  horizontally.     The  upper  two  connect  the  parietal,  and  the 
lower  two  the  temporal  with  the  occipital  lobe. 

5.  Central  lobe,  or  island  of  Eeil,  which  contains  a  number  of  radi- 
ating convolutions  (gyri  operti). 

When  the  cerebral  hemispheres  have  been  removed  by  transverse  cuts 
at  a  level  of  the  corpus  callosum,  and  that  body  has  been  cut  through  on 
either  side  about  half  an  inch  from  the  middle  line  by  an  anteroposte- 
rior vertical  incision,  a  considerable  space  on  either  side  of  the  middle 


THK    CEBEBKO-SPINAL    NERVOUS    SYSTEM. 


505 


line  in  the  interior  of  the  brain  is  laid  open,  called  the  lateral  ventricles. 
They  are  separated  by  a  thin  double  partition,  the  septum  lucidum,  be- 
tween the  lamina?  of  which  is  an  interval  containing  fluid,  the  fifth  ven- 
tricle; they  communicate  by  an  aperture  below.  They  are  lined  with 
ciliated  epithelium.  Each  ventricle  consists  of  a  narrow  interval  extend- 
ing into  the  anterior  and  posterior  regions  from  the  middle  region  of 
the  corresponding  hemisphere.  Its  middle  portion  or  body  is  straight, 
but  each  horn  is  more  or  less  curved.  In  the  floor  of  the  cavity  project 
portions  of  the  chief  basal  ganglia,  the  corpus  striatum  in  front,  and  the 
optic  thalamus  behind,  and  a  white  band  of  tibres,  the  taenia  semicircu- 
laris,  between  them.    For  the  relation  of  the  other  portions  of  the  interior 


Fig.  345. — View  of  the  Corpus  Callosum  from  above.  M.— The  upper  surface  of  the  corpus  eal- 
losum  has  been  fully  exposed  by  separating  the  cerebral  hemispheres  and  throwing  them  to  the 
side;  the  gyrus  fornicatus  has  been  detached,  and  the  transverse  fibres  of  the  corpus  callosum 
traced  for  some  distance  into  the  cerebral  medullary  substance.  1,  the  upper  surface  of  the  corpus 
callosum;  2,  median  furrow  or  raphe;  3,  longitudinal  strias  bounding  the  furrow:  4.  swelling  formed 
by  the  transverse  bauds  as  they  pass  into  the  cerebrum;  5.  anterior  extremity  or  knee  of  the  cor- 
pus callosum;  6,  posterior  extremity;  7,  anterior,  and  8,  posterior  part  of  the  mass  of  fibres  pro- 
ceeding from  the  corpus  callosum;  9,  margin  of  the  swelling;  10,  anterior  part  of  the  convolution 
of  the  corpus  callosum;  11,  hem  or  band  of  union  of  this  convolution;  12,  internal  convolutions 
of  the  parietal  lobe;  13,  upper  surface  of  the  cerebellum.    ( Sappey  after  Foville.  i 

of  the  brain — including  those  of  the  arched  white  commissure  or  fornix 
which  extends  backwards  from  the  septum  lucidum,  and  consists  of  two 
lateral  halves  joined  only  in  the  middle,  with  two  anterior  pillars  and 
two  posterior  crura — and  of  the  third  ventricle,  refer  to  Fig.  342  and  the 
description. 

The  Internal  Surface  (Fig.  -'UT)  contains  the  following  gyri  and 
sulci: 


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HANDBOOK    OF    PHYSIOLOGY. 


Gyrus  fomicatus,  a  long  curved  convolution,  parallel  to  and  curving 
round  the  corpus  callosum,  and  swelling  out  at  its  hinder  and  upper  end 


Sir*"! 


-T» 


Fig.  846.— View  of  the  brain  from  above  (semi-diagrammatic).     SI,  end  of  horizontal  ramus 
of  Assure  of  Sylvius.    The  other  letters  refer  to  the  same  parts  as  in  Fig.  344.     (Eeker.) 

into  the  quadrate  lobule   (precuneus),  which  is  continuous  with  the 
superior  parietal  lobule  on  the  external  surface. 


A    9 


'IP 


Fig.  347. — View  of  the  right  hemisphere  m  the  median  aspect  (semi-diagrammatic).  CC,  cor- 
pus callosum  longitudinally  divided;  Gf,  gyrus  fomicatus;  H,  gyrus  hippocampi;  h,  sulcus  hippo- 
campi; U,  uncinate  gyrus;  cm,  calloso-marginal  fissure;  Fl,  median  aspect  of  first  frontal  con- 
volution; c,  terminal  portion  of  sulcus  centralis  (fissure  of  Rolando);  A,  ascending  frontal:  B. 
ascending  parietal  convolution;  PI',  praecuneus;  Oz,  cuneus;  po,  parietooccipital  fissure;  o,  sulcus 
occipitalis  transversus;  oc,  calcarine  fissure;  oc',  superior;  oc",  inferior  ramus  of  the  same;  D. 
gyrus  descendens;  T4,  gyrus  occipito-temporalis  lateralis  Gobulus  fusiformis);  T5,  gyrus  occipito- 
temporalis  medialis  (lobulus  lingualis).    (Ecker.) 


THE    CEREBROSPINAL    NERVOUS    SYSTEM. 


50? 


Marginal  convolution  runs  parallel  to  the  preceding,  and  occupies  the 
space  between  it  and  the  edge  of  the  longitudinal  fissure. 

The  two  convolutions  are  separated  by  the  calloso-marginal  fissure. 

The  internal  perpendicular  fissure  is  well  marked,  and  runs  down- 
wards to  its  juuction  with  the  calcarine  fissure:  the  wedge-shaped  mass 
intervening  betweeu  these  two  is  termed  the  cuneus.     The  calcarine  fis- 


y 


i    7  '      / 

'J,  mAlW/  \Wi 


Fig.  848. 


t 


Fig. 

349. 

1 

;/»V3 

II 

Fig.  3.50. 


Fig.  34^.— The  layers  of  the  cortical  grav  matter  of  the  cerebrum.    (Meynert.1 
Fig.  350.-t  Drawn  by  G.  Munro  Smith  from  ammonium  bichromate  preparations  by  E.  (. . 
Bons!i> 

sure  corresponds  to  the  projection  into  the  posterior  cornu  of  the  lateral 
ventricle,  termed  the  Hippocampus  minor.  The  temporosphenoidal  lobe 
on  its  internal  aspect  is  seen  to  end  in  a  hook  (uncinate  gyrus).  The 
notch  round  which  it  curves  is  continued  up  and  back  as  the  dentate  or 


508  HANDBOOK    OF    PHYSIOLOGY. 

hippocanipal  sulcus:  this  fissure  underlies  the  projection  of  the  hippo- 
campus major  within  the  brain.  There  are  three  internal  temporo-occi- 
pital  convolutions,  of  which  the  superior  and  inferior  ones  are  usually- 
well  marked,  the  middle  one  generally  less  so*. 

The  collateral  fissure  (corresponding  to  the  eminentia  collateralis) 
forms  the  lower  boundary  of  the  superior  temporo-occipital  convolution. 

All  the  above  details  will  be  found  indicated  in  the  diagrams  (Figs. 
346,  347). 

Structure. — The  cerebrum  is  constructed,  like  the  other  chief  divi- 
sions of  the  cerebro-spinal  system,  of  gray  and  white  matter;  and,  as  in 
the  case  of  the  Cerebellum  (and  unlike  the  spinal  cord  and  medulla  ob- 
longata), the  gray  matter  (cortex)  is  external,  and  forms  a  capsule  or 
covering  for  the  white  substance.  For  the  evident  purpose  of  increasing 
its  amount  without  undue  occupation  of  space,  the  gray  matter  is  vari- 
ously infolded  so  as  to  form  the  cerebral  convolutions. 

The  cortical  gray  matter  of  the  brain  consists  of  five  layers  (Mey- 
nert)  (Fig.  348). 

1.  Superficial  layer  with  abundance  of  neuroglia  and  a  few  small 
multipolar  ganglion-cells.  2.  A  large  number  of  closely  packed  small 
ganglion-cells  of  pyramidal  shape.  3.  The  most  important  layer,  and 
the  thickest  of  all:  it  contains  many  large  pyramidal  ganglion-cells,  each 
with  a  process  running  off  from  the  apex  vertically  towards  the  free  sur- 
face, and  lateral  processes  at  the  base  which  are  always  branched.  Also 
a  median  process  from  the  base  of  each  cell  which  is  unbranched  and 
becomes  continuous  with  the  axis-cylinder  of  a  nerve-fibre.  4.  Numerous 
ganglion-cells:  termed  the  "granular  formation"  by  Meynert.  .5. 
Spindle-shaped  and  branched  ganglion-cells  of  moderate  size  arranged 
chiefly  parallel  to  the  free  surface  (vide  Fig.  348). 

According  to  recent  observations  by  Bousfield,  the  fibres  of  the  me- 
dullary centre  become  connected  with  the  multipolar  ganglion-cells  of 
the  fourth  layer,  and,  from  these  latter,  branches  pass  to  the  angles  at 
the  bases  of  the  pyramidal  cells  of  the  third  layer  of  the  cortex  (Fig.  350, 
a).  From  the  apices  of  the  pyramidal  cells,  the  axis-cylinder  processes 
pass  upwards  for  a  considerable  distance,  and  finally  terminate  in  ovoid 
corpuscles  (Fig.  349),  closely  resembling,  and  homologous  with,  the  cor- 
puscles in  which  the  ultimate  ramifications  of  the  branched  cells  of  Pur- 
kinje  in  the  cerebellum  terminate.  Thus  it  would  seem  that  the  large 
pyramidal  cells  of  the  third  layer  are  themselves  homologous  with  the 
cells  of  Purkinje  in  the  cerebellum. 

The  white  matter  of  the  brain,  as  of  the  spinal  cord,  consists  of 
bundles  of  medullated,  and,  in  the  neighborhood  of  the  gray  matter,  of 
non-medullated  nerve-fibres,  which,  however,  as  is  the  case  in  the  cen- 
tral nervous  system  generally,  have  no  external  nucleated  nerve-sheath, 
which  are  held  together  by  delicate  connective  tissue.  The  size  of  the 
fibres  of  the  brain  is  usually  less  than  that  of  the  fibres  of  the  spinal 
cord:  the  average  diameter  of  the  former  being  about  TirJ-oT  °f  an  mcn- 


THE    CEREBROSPINAL    NERVOUS    SYSTEM.  509" 

Chemical  Composition. — The  chemistry  of  nerves  and  nerve  cells  has 
been  chief!}'  studied  in  the  brain  and  spinal  cord.  Nerve  matter  con- 
tains several  albuminous  and  fatty  bodies  (cerebrin,  lecithin,  and  some 
others),  also  fatty  matter  which  can  be  extracted  by  ether  (including 
cholesterin)  and  various  salts,  especially  Potassium  and  Magnesium 
phosphates,  which  exist  in  larger  quantity  than  those  of  Sodium  and 
Calcium. 

The  great  relative  and  absolute  size  of  the  Cerebral  hemispheres  in 
the  adult  man,  masks  to  a  great  extent  the  real  arrangement  of  the  sev- 
eral parts  of  the  brain,  which  is  illustrated  in  the  two  accompanying 
diagrams. 

From  these  it  is  apparent  that  the  parts  of  the  brain  are  disposed  in 
a  linear  series,  as  follows  (from  before  backwards):  olfactory  lobes, 
cerebral  hemispheres,  optic  thalami,  and  third  ventricle,  corpora  quadri- 
gemina,  or  optic  lobes,  cerebellum,  medulla  oblongata. 

This  linear  arrangement  of  parts  actually  occurs  in  the  human  foetus; 
and  it  is  permanent  in  some  of  the  lower  Vertebrata,  e.  g.,  Fishes,  in 
which  the  cerebral  hemispheres  are  represented  by  a  pair  of  ganglia 
intervening  between  the  olfactory  and  the  optic  lobes,  and  considerably 
smaller  than  the  latter.  In  Amphibia  the  cerebral  lobes  are  further  de- 
veloped, and  arc  larger  than  any  of  the  other  ganglia. 

In  Eeptiles  and  Birds  the  cerebral  ganglia  attain  a  still  further  devel- 
opment, and  in  Mammalia  the  cerebral  hemispheres  exceed  in  weight  all 
the  rest  of  the  brain.  As  we  asceud  the  scale,  the  relative  size  of  the 
cerebrum  increases,  till  in  the  higher  apes  and  man  the  hemispheres, 
which  commenced  as  two  little  lateral  buds  from  the  anterior  cerebral 
vesicle,  have  grown  upwards  and  backwards,  completely  covering  in  and 
hiding  from  view  all  the  rest  of  the  brain.  At  the  same  time  the  smooth 
surface  of  the  brain,  in  many  lower  Mammalia,  such  as  the  rabbit,  is 
replaced  by  the  labyrinth  of  convolutions  of  the  brain. 

Weight  of  the  Brain. — The  brain  of  an  adult  man  weighs  from  48 
to  50  oz. — or  about  3  lbs.  It  exceeds  in  absolute  weight  that  of  all  the 
lower  animals  except  the  elephant  and  whale.  Its  weight,  relatively  to 
that  of  the  body,  is  only  exceeded  by  that  of  a  few  small  birds,  and  some 
of  the  smaller  monkeys.  In  the  adult  man  it  ranges  from  ■£$-■£$  of  the 
body  weight. 

Variations.  Age. — In  a  new-born  child  the  brain  (weighing  10-14 
oz.)  is  T\r  of  the  body  weight.  At  the  age  of  7  years  the  brain  already 
averages  40  oz. ,  and  about  14  years  the  brain  not  ^infrequently  reaches 
the  weight  of  48  oz.  Beyond  the  age  of  forty  years  the  weight  slowly 
but  steadily  declines  at  the  rate  of  about  1  oz.  in  10  years. 

Sex. — The  average  weight  of  the  female  brain  is  less  than  the  male: 
and  this  difference  persists  from  birth  throughout  life.  In  the  adult  it 
amounts  to  about  5  oz.  Thus  the  average  weight  of  an  adult  woman's 
brain  is  about  44  oz. 

I iitelligence. — The  brains  of  idiots  are  generally  much  below  the 
average,  some  weighing  less  than  16  oz.  Still  the  facts  at  present  eol- 
lected  do  not  warrant  more  than  a  very  general  statement,  to  which  there 
arc  numerous  exceptions,  that  the  brain  weight  corresponds  to  some 
extent  with  the  degree  of  intelligence.     There  can  be  little  doubt  that 


510 


HANDBOOK    OF    PHYSIOLOGY. 


the  complexity  and  depth  of  the  convolutions,  which  indicate  the  area  of 
the  gray  matter  of  the  cortex,  correspond  with  the  degree  of  intelligence. 

Weight  of  the  Spinal  Cord.-  The  spinal  cord  of  man  weighs  from 
1-1  £  oz. ;  its  weight  relatively  to  the  brain  is  about  1  :  36.  As  we  de- 
scend the  scale,  this  ratio  constantly  increases  till  in  the  mouse  it  is  1  :  4. 
In  cold-blooded  animals  the  relation  is  reversed,  the  spinal  cord  is  the 
heavier  and  the  more  important  organ.  In  the  newt,  2:1;  and  in  the 
lamprey,  75  :  1. 

Distinctive  Characters  of  the  Human  Brain. — The  following 
characters  distinguish  the  brain  of  man  and  apes  from  those  of  all  other 
animals,  (a.)  The  rudimentary  condition  of  the  olfactory  lobes,  (b.) 
A  perfectly  defined  fissure  of  Sylvius,     (c.)  A  posterior  lobe  completely 


Fig.  351. 


Fig.  352. 


Fig.  351.— Diagrammatic  horizontal  section  of  a  Vertebrate  brain.  The  figures  serve  both  for 
this  and  the  next  diagram.  Mb,  mid  brain:  what  lies  in  front  of  this  is  the  fore-,  and  what  lies 
behind,  the  hind-brain;  Lt,  lamina  terminalis;  Olf,  olfactory  lobes;  Hmp,  hemispheres;  Th.  E, 
thalamencephalon ;  Pn,  pineal  gland;  Py,  pituitary  body;  F.  M,  foramen  of  Munro;  cs,  corpus 
striatum;  Th,  optic  thalamus;  CC,  crura  cerebri:  the  mass  lying  above  the  canal  represents  the 
the  corpora  quadrigemina ;  Cb,  cerebellum;  I— IX.,  the  nine  pairs  of  cranial  nerves;  1,  olfactory 
ventricle;  2,  lateral  ventricle;  3,  third  ventricle;  4,  fourth  ventricle;  +,  iter  a  tertio  ad  quartum 
ventriculum.    (Huxley.) 

Fig.  352. — Longitudinal  and  vertical  Diagrammatic  section  of  a  vertebrate  brain.  Letters  as 
before.    Lamina  terminalis  is  represented  by  the  strong  black  line  joining  Pn  and  Py.    (Huxley.) 


covering  the  cerebellum,     (d.)  The  presence  of  posterior  cornua  in  the 
lateral  ventricles. 

The  most  distinctive  points  in  the  human  brain,  as  contrasted  with 
that  of  apes,  are: — (1.)  The  much  greater  size  and  weight  of  the  whole 
brain.  The  brain  of  a  full-grown  gorilla  weighs  only  about  15  oz.,  which 
is  less  than  -J  the  weight  of  the  human  adult  male  brain,  and  barely  ex- 
ceeds that  of  the  human  infant  at  birth.  (2.)  The  much  greater  com- 
plexity of  the  convolutions,  especially  the  existence  in  the  human  brain 


THE    CEREBROSPINAL    NERVOUS    SYSTEM. 


511 


of  tertiary  convolutions  in  the  sides  of  the  fissures.  (3.)  The  greater 
relative  size  and  complexity,  and  the  blunted  quadrangular  contour  of 
the  frontal  lobes  in  man,  which  are  relatively  both  broader,  longer,  and 
higher,  than  in  apes.  In  apes  the  frontal  lobes  project  keel-like  (ros- 
trum) between  the  olfactory  bulbs.  (4.)  The  much  greater  prominence 
of  the  temporo-sphenoidal  lobes  in  apes.  (5.)  The  fissure  of  Sylvius  is 
nearly  horizontal  in  man,  while  in  apes  it  slants  considerably  upwards. 
(6.)  The  distinctness  of  the  external  perpendicular  fissure,  which  in  apes 
is  a  well-defined  almost  vertical  "slash,"  while  in  man  it  is  almost 
obscured  by  the  annectent  gyri. 


Fig.  353.— Brain  of  the  Orang,  zi  natural  size,  showing  the  arrangement  of  the  convolutions. 
Sy,  fissure  of  Sylvius:  R,  fissure  of  Rolando;  E  P,  external  perpendicular  Assure:  01  f,  olfactory 
lobe;  Cb,  cerebellum;  P  V,  pons  Varolii;  M  O.  medulla  oblongata  As  contrasted  with  the  human 
brain,  the  frontal  lobe  is  short  and  small,  relatively,  the  fissure  of  Sylvius  is  oblique,  the  temporo- 
sphenoidal  lobe  very  prominent,  and  the  external  perpendicular  fissure  very  well  marked.  (Gratio- 
let.) 

Most  of  the  above  points  are  shown  in  the  accompanying  figure  of  the 
brain  of  the  Orang. 


Functions  of  the  Cerebrum. 

Speaking  in  the  most  general  way,  and  for  the  present  omitting  the 
accumulating  evidence  in  favor  of  the  direct  representation  of  the  vari- 
ous co-ordinated  movements  of  the  muscles  of  the  body  in  ganglia  situ- 
ated in  different  parts  of  the  cerebral  cortex,  it  may  be  said  that: — (1.) 
The  Cerebral  hemispheres  are  the  organs  by  which  are  perceived  those 
clear  and  more  impressive  sensations  which  can  be  retained,  and  regard- 
ing which  we  can  judge.  (2.)  The  Cerebrum  is  the  organ  of  the  will,  in 
so  far  at  least  as  each  act  of  the  will  requires  a  deliberate,  however  quick 
determination.  (3.)  It  is  the  means  of  retaining  impressions  of  sensible 
things,  and  reproducing  them  in  subjective  sensations  and  ideas.  (-4.) 
It  is  the  medium  of  all  the  higher  emotions  and  feelings,  and  of  the 


512  HANDBOOK    OF   PHTSIOLOGT. 

faculties   of  judgment,  understanding,  memory,  reflection,  induction, 
imagination  and  the  like. 

Evidence  regarding  the  physiology  of  the  cerebral  hemispheres  has 
been  obtained,  as  in  the  case  of  other  parts  of  the  nervous  system,  from 
the  study  of  Comparative  Anatomy,  from  Pathology,  and  from  Experi- 
ments on  the  lower  animals.  The  chief  evidences  regarding  the  func- 
tions of  the  Cerebral  hemispheres  derived  from  these  various  sources,  are 
briefly  these: — 1.  Any  severe  injury  of  them,  such  as  a  general  concus- 
sion, or  sudden  pressure  by  apoplexy,  may  instantly  deprive  a  man  of  all 
power  of  manifesting  externally  any  mental  faculty.  2.  In  the  same 
general  proportion  as  the  higher  mental  faculties  are  developed  in  the 
Vertebrate  animals,  and  in  man  at  different  ages  and  in  different  indi- 
viduals, the  more  is  the  size  of  the  cerebral  hemispheres  developed  in  com- 
parison with  the  rest  of  the  cerebro-spinal  system.  3.  No  other  part  of 
the  nervous  system  bears  a  corresponding  proportion  to  the  development 
of  the  mental  faculties.  4.  Congenital  and  other  morbid  defects  of  the 
cerebral  hemisphere  are,  in  general,  accompanied  by  corresponding 
deficiency  in  the  range  or  power  of  the  intellectual  faculties  and  the 
higher  instincts.  5.  Eemoval  of  the  cerebral  hemispheres  in  one  of  the 
lower  animals  produces  effects  corresponding  with  what  might  be  antici- 
pated from  the  foregoing  facts. 

Effects  of  the  Removal  of  the  Cerebrum. — The  removal  of  the  cerebrum 
in  the  lower  animals  appears  to  reduce  them  to  the  condition  of  a  mech- 
anism without  spontaneity.  A  pigeon  from  which  the  cerebrum  has  been 
removed  will  remain  motionless  and  apparently  unconscious  unless  dis- 
turbed. When  disturbed  in  any  way  it  soon  recovers  its  former  position; 
when  thrown  into  the  air  it  flies. 

In  the  case  of  the  frog,  when  the  cerebral  lobes  have  been  removed, 
the  animal  appears  similarly  deprived  of  all  power  of  spontaneous  move- 
ment. '  But  it  sits  up  in  a  natural  attitude,  breathing  quietly;  when 
pricked  it  jumps  away;  when  thrown  into  the  water  it  swims;  when 
placed  upon  the  palm  of  the  hand  it  remains  motionless,  although,  if  the 
hand  be  gradually  tilted  over  till  the  frog  is  on  the  point  of  losing  his 
balance,  he  will  crawl  up  till  he  regains  his  equilibrium,  and  comes  to  be 
perched  quite  on  the  edge  of  the  hand.  This  condition  contrasts  with 
that  resulting  from  the  removal  of  the  entire  brain,  leaving  only  the 
spinal  cord;  in  this  case  only  the  simpler  reflex  actions  can  take  place. 
The  frog  does  not  breathe,  he  lies  flat  on  the  table  instead  of  sitting  up; 
when  thrown  into  a  vessel  of  water  he  sinks  to  the  bottom;  when  his 
legs  are  pinched  he  kicks  out,  but  does  not  leap  away. 

Unilateral  Action. — Respecting  the  mode  in  which  the  brain  dis- 
charges its  functions,  there  is  no  evidence  whatever.  But  it  appears 
that,  for  all  but  its  highest  intellectual  acts,  one  of  the  cerebral  hemi- 
spheres is  sufficient.     For  numerou  scases  are  recorded  in  which  no  men- 


THE    CEREBROSPINAL    NERV0U8    SYSTEM.  513 

tal  defect  was  observed,  although  one  cerebral  hemisphere  was  so  disor- 
ganized or  atrophied  that  it  could  not  be  supposed  capable  of  discharging 
its  functions.  The  remaining  hemisphere  was,  in  these  cases,  adequate 
to  the  functions  generally  discharged  by  both;  but  the  mind  does  not 
seem  in  any  of  these  cases  to  have  been  tested  in  very  high  intellectual 
exercises;  so  that  it  is  not  certain  that  one  hemisphere  will  suffice  for 
these.  In  general,  the  brain  combines,  as  one  sensation,  the  impressions 
which  it  derives  from  one  object  through  both  hemispheres,  and  the 
ideas  to  which  the  two  such  impressions  give  rise  are  single.  In  relation 
to  common  sensation  and  the  effort  of  the  will,  the  impressions  to  and  from 
the  hemispheres  of  the  brain  are  carried  across  the  middle  line;  so  that  in 
destruction  or  compression  of  either  hemisphere,  whatever  effects  are  pro- 
duced in  loss  of  sensation  or  voluntary  motion,  are  observed  on  the  side 
of  the  body  opposite  to  that  on  which  the  brain  is  injured. 

Localization  of  Functions. — In  speaking  of  the  cerebral  hemispheres 
as  the  so-called  organs  of  the  mind,  they  have  been  regarded  as  if  they 
were  single  organs,  of  which  all  parts  are  equally  appropriate  for  the  ex- 
ercise of  each  of  the  mental  faculties.  But  it  is  possible  that  each 
faculty  has  a  special  portion  of  the  brain  appropriated  to  it  as  its  proper 
organ.  For  this  theory  the  principal  evidences  are  as  follows: — 1.  That 
it  is  in  accordance  with  the  physiology  of  the  compound  organs  or  sys- 
tems in  the  body,  in  which  each  part  has  its  special  function;  as,  for 
example,  of  the  digestive  system,  in  Avhich  the  stomach,  liver,  and  other 
organs  perform  each  their  separate  share  in  the  general  process  of  the 
digestion  of  the  food.  2.  That  in  different  individuals  the  several  men- 
tal functions  are  manifested  in  very  different  degrees.  Even  in  early 
childhood,  before  education  can  be  imagined  to  have  exercised  any  in- 
fluence on  the  mind,  children  exhibit  various  dispositions — each  presents 
some  predominant  propensity,  or  evinces  a  singular  aptness  in  some 
study  or  pursuit;  and  it  is  a  matter  of  daily  observation  that  every  one 
has  his  peculiar  talent  or  propensity.  But  it  is  difficult  to  imagine  how 
this  could  be  the  case,  if  the  manifestation  of  each  faculty  depended  on 
the  whole  of  the  brain;  different  conditions  of  the  whole  mass  might 
affect  the  mind  generally,  depressing  or  exalting  all  its  functions  in  an 
equal  degree,  but  could  not  permit  one  faculty  to  be  strongly  and  another 
weakly  manifested.  3.  The  plurality  of  organs  in  the  brain  is  supported 
by  the  phenomena  of  some  forms  of  mental  derangement.  It  is  not 
usual  for  all  the  mental  faculties  in  an  insane  person  to  be  equally  dis- 
ordered; it  of  ten  happens  that  the  strength  of  some  is  increased,  while  that 
of  others  is  diminished;  and  in  many  cases  one  function  only  of  the 
brain  is  deranged,  while  all  the  rest  are  performed  in  a  natural  manner. 
4.  The  same  opinion  is  supported  by  the  fact  that  the  several  mental 
faculties  are  developed  to  their  greatest  strength  at  different  periods  of 
life,  some  being  exercised  with  great  energy  in  childhood,  others  only  in 


514  HANDBOOK    OF    PHYSIOLOGY. 

adult  age;  and  that,  as  their  energy  decreases  in  old  age,  there  is  not  a 
gradual  and  equal  diminution  of  power  in  all  of  them  at  once,  but,  on 
the  contrary,  a  diminution  in  one  or  more,  while  others  retain  their  full 
strength,  or  even  increase  in  power.  5.  The  plurality  of  cerebral  organs 
appears  to  be  indicated  by  the  phenomena  of  dreams,  in  which  only  a 
part  of  the  mental  faculties  are  at  rest  or  asleep,  while  the  others  are 
awake,  and,  it  is  presumed,  are  exercised  through  the  medium  of  the 
parts  of  the  brain  appropriated  to  them. 

Unconscious  Cerebration. — In  connection  with  the  above,  some 
remarkable  phenomena  should  be  mentioued  which  have  been  described 
as  depending  on  an  unconscious  action  of  the  brain. 

It  must  be  within  the  experience  of  every  one  to  have  tried  to  recol- 
lect some  particular  name  or  occurrence;  and  after  trying  in  vain  for 
some  time  the  attempt  is  given  up  and  quite  forgotten  amid  other  occu- 
pations, when  suddenly,  hours  or  even  a  day  or  two  afterwards,  the 
desired  name  or  occurrence  unexpectedly  flashes  across  the  mind.  Such 
occurrences  are  supposed  by  many  to  be  due  to  the  requisite  cerebral 
processes  going  on  unconsciously,  and,  when  the  result  is  reached,  to  our 
all  at  once  becoming  conscious  of  it. 

That  unconscious  cerebration  may  sometimes  occur,  is  likely  enough; 
and  it  is  paralleled  by  the  unconscious  walking  of  a  somnambulist.  But 
many  cases  of  so-called  unconscious  cerebration  are  better  explained  by 
the  supposition  that  some  missing  link  in  the  chain  of  reasoning  cannot 
at  the  moment  be  found;  but  is  afterwards,  by  some  chance  combination 
of  events,  suggested,  and  thus  the  mental  process  is  at  once,  with  the 
memory  of  what  has  gone  before,  completed. 

Again,  in  the  vain  endeavor  to  solve  a  difficult,  or  it  may  be  an  easy 
problem,  the  reasoner  is  frequently  in  the  condition  of  a  man  whose 
wearied  muscles  could  never,  before  they  have  rested,  overcome  some 
obstacles.  In  both  cases,— of  brain  and  muscle,  after  renewal  of  their 
textures  by  rest,  the  task  is  performed  so  rapidly  as  to  seem  instan- 
taneous. 

Sleep. — All  parts  of  the  body  which  are  the  seat  of  active  change 
require  periods  of  rest.  The  alternation  of  work  and  rest  is  a  necessary 
condition  of  their  maintenance,  and  of  the  healthy  performance  of  their 
functions.  These  alternating  periods,  however,  differ  much  in  duration 
in  different  cases;  but,  for  any  individual  instance,  they  preserve  a  gen- 
eral and  rather  close  uniformity.  Thus,  as  before  mentioned,  the  periods 
of  rest  and  work,  in  the  case  of  the  heart,  occupy,  each  of  them,  about 
half  a  second;  in  the  case  of  the  ordinary  respiratory  muscles  the  periods 
are  about  four  or  five  times  as  long.  In  many  cases,  again  (as  of  the 
voluntary  muscles  during  violent  exercise)  while  the  periods  during 
active  exertion  alternate  very  frecuently,  yet  the  expenditure  goes  far 
ahead  of  the  repair,  and,  to  compensate  for  this,  an  after  repose  of  some 
hours  become  necessary;  the  rhythm  being  less  perfect  as  to  time,  than 
in  the  case  of  the  muscles  concerned  in  circulation  and  respiration. 

Obviously,  it  would  be  impossible  that,  in  the  case  of  the  Brain,  there 
should  be  short  periods  of  activity  and  repose,  or  in  other  words,  of  con- 
sciousness and  unconsciousness.  The  repose  must  occur  at  long  inter- 
vals; and  it  must  therefore  be  proportionately  long.     Hence  the  necessity 


THE    CEREBROSPINAL    NERVOUS    SYSTEM.  51) 

for  that  condition  which  we  cull  Sleep  ;  a  condition  which,  seeming  at 
first  sight  exceptional,  is  only  an  unusually  perfect  example  of  what 
occurs,  at  varying  intervals,  in  every  actively  working  portion  of  our 
bodies. 

A  temporary  abrogation  of  the  functions  of  the  cerebrum  imitating 
sleep,  may  occur,  in  the  case  of  injury  or  disease,  as  the  consequence  of 
two  apparently  widely  different  conditions.  Insensibility  is  equally  pro- 
duced by  a  deficient  and  an  excessive  quantity  of  blood  in  the  cranium 
(coma);  but  it  was  once  supposed  that  the  latter  offered  the  truest 
analogy  to  the  normal  condition  of  the  brain  in  sleep,  and  in  the  absence 
of  any  proof  to  the  contrary,  the  brain  was  said  to  be  during  sleep  con- 
gested. Direct  experimental  inquiry  has  led,  however,  to  the  opposite 
conclusion. 

By  exposing,  at  a  circumscribed  spot,  the  surface  of  the  brain  of  living 
animals,  and  protecting  the  exposed  part  by  a  watch-glass.  Durham  was 
able  to  prove  that  the  brain  becomes  visibly  paler  (anaemic)  during 
sleep;  and  the  anaemia  of  the  optic  disc  during  sleep,  observed  by  Hugh- 
lings  Jackson,  may  be  taken  as  a  strong  confirmation,  by  analogy,  of  the 
same  fact. 

A  very  little  consideration  will  show  that  these  experimental  results 
correspond  exactly  with  what  might  have  been  foretold  from  the  analogy 
of  other  physiological  conditions.  Blood  is  supplied  to  the  brain  for 
two  partly  distinct  purposes.  (1.)  It  is  supplied  for  mere  nutrition's 
sake.  (2.)  It  is  necessary  for  bringing  supplies  of  potential  or  active 
energy  (i.  e.,  combustible  matter  or  heat)  which  may  be  transformed  by 
the  cerebral  corpuscles  into  the  various  manifestations  of  nerve-force. 
During  sleep,  blood  is  requisite  for  only  the  first  of  these  purposes;  and 
its  supply  in  greater  quantity  would  be  not  only  useless,  but,  by  suppl- 
ing an  excitement  to  work,  when  rest  is  needed,  would  be  positively 
harmful.  In  this  respect  the  varying  circulation  of  blood  in  the  brain 
exactly  resembles  that  which  occurs  in  all  other  energy  transforming 
parts  of  the  body;  e.  g.,  glands  or  muscles. 

At  the  same  time,  it  is  necessary  to  remember  that  the  normal  anaemia 
of  the  brain  which  accompanies  sleep  is  probably  a  result,  and  not  a 
cause  of  the  quiescence  of  the  cerebral  functions.  What  the  immediate 
cause  of  this  periodical  partial  abrogation  of  function  is,  however,  we  do 
not  know. 

Somnambulism  and  Dreams. — What  we  term  sleep  occurs  often  in 
very  different  degrees  in  different  parts  of  the  nervous  system;  and  in 
some  parts  the  expression  cannot  be  used  in  the  ordinary  sense. 

The  phenomena  of  dreams  and  somnambulism  are  examples  of  differ- 
ing degrees  of  sleej)  in  different  parts  of  the  cerebro-spinal  nervous 
system.  In  the  former  case  the  cerebrum  is  still  partially  active;  but 
the  mind-products  of  its  action  are  no  longer  corrected  by  the  reception, 
on  the  part  of  the  sleeping  sensoriam,  of  impressions  of  objects  belong- 
ing to  the  outer  world;  neither  can  the  cerebrum,  in  this  half-awake 
condition,  act  on  the  centres  of  reflex  action  of  the  voluntary  muscles, 
so  as  to  cause  the  latter  to  contract — a  fact  within  the  painful  experience 
of  all  who  have  suffered  from  nightmare. 

In  somnambulism  the  cerebrum  is  capable  of  exciting  that  train  <>f 
reflex  nervous  action  which  is  necessary  for  progression,  while  the  nerve- 
centre  of  muscular  sense  (in  the  cerebellum  ?)  is,  presumably,  fully 
awake;  but  the  sensorium  is  still  asleep,  and  impressions  made  on  it  are 


516  HANDBOOK    OF    PHYSIOLOGY. 

not  sufficiently  felt  to  rouse  the  cerebrum  to  a  comparison  of  the  differ- 
ence between  mere  ideas  or  memories  and  sensations  derived  from  exter- 
nal objects. 

The  Motor  Centres  of  the  Cerebral  Cortex. 

The  experiments  upon  the  brains  of  various  animals  by  means  of  elec- 
trical stimulation  have  demonstrated  that  there  are  definite  regions  of 
the  cerebral  cortex  the  stimulation  of  which  produces  definite  movements 
of  co-ordinated  groups  of  muscle  of  the  opposite  side  of  the  body.  It 
had  long  been  well-known  that  the  cerebral  hemispheres  could  not  be 
excited  by  mechanical,  chemical,  or  thermal  stimuli,  but  Fritsch  and 
Hitzig  were  the  first  to  show  that  they  are  amenable  to  electric  irritation. 
They  employed  a  weak  constant  current  in  their  experiments,  applying 
a  pair  of  fine  electrodes  not  more  than  -?\  in.  apart  to  different  parts  of 
the  cerebral  cortex.  The  results  thus  obtained  have  been  confirmed  and 
extended  by  Ferrier  and  many  others. 

The  fundamental  phenomena  observed  in  all  these  cases  may  be  thus 
epitomized: — 

(1).  Excitation  of  the  same  spot  is  always  followed  by  the  same  move- 
ment in  the  same  animal.  (2).  The  area  of  excitability  for  any  given 
movement  is  extremely  small,  and  admits  of  very  accurate  definition.  (3). 
In  different  animals  excitations  of  anatomically  corresponding  spots  pro- 
duce similar  or  corresponding  results. 

The  various  definite  movements  resulting  from  the  electric  stimula- 
tion of  circumscribed  areas  of  the  cerebral  cortex,  are  enumerated  in  the 
description  of  the  accompanying  figures  of  the  dog  and  monkey's  brain. 

In  the  case  of  the  dog,  the  results  obtained  are  summed  up  as  follows, 
by  Hitzig: — 

(a).  One  portion  (anterior)  of  the  convexity  of  the  cerebrum  is  motor; 
another  portion  (posterior)  is  non-motor,  (b).  Electric  stimulation  of 
the  motor  portion  produces  co-ordinated  muscular  contraction  on  the 
opposite  side  of  the  body.  (c).  With  very  weak  currents,  the  contrac- 
tions produced  are  distinctly  limited  to  particular  groups  of  muscles; 
with  stronger  currents  the  stimulus  is  communicated  toother  muscles  of 
the  same  or  neighboring  parts,  (d).  The  portions  of  the  brain  inter- 
vening between  these  motor  centres  are  inexcitable  by  similar  means. 

With  regard  to  the  facts  above  mentioned,  all  experimenters  are  agreed, 
but  there  is  still  considerable  diversity  of  opinion  as  to  their  explanation. 

In  applying  the  facts  ascertained  by  these  experiments  to  elucidate 
the  physiology  of  the  human  brain,  we  must  remember  that  the  method 
of  electric  stimulation  is  an  artificial  one,  differing  widely  from  the  ordi- 
nary stimuli  to  which  the  brain  is  subject  during  life. 

Effects  of  Stimulation  of   Various  Regions  of  a  Monhey's  Brain. — 


THE    CEREBROSPINAL    NERVOUS    SYSTEM. 


517 


According  to  the  observations  of  Ferrier,  confirmed  and  extended  by  later 
experimenters,  stimulation  of  various  parts  of  the  monkey's  brain,  as  in- 
dicated by  the  numbers  in  Figs.  356,  357,  produces  movements  of 
definite  muscles,  thus: — 

Stimulation  of  the  districts  marked  1,  causes  movements  of  hind  foot; 
•of  2,  chiefly  adduction  of  the  foot;  of  3,  movements  of  hind  foot  and  tail; 


s 

Fig.  355. 
Figs.  354  and  355.— Brain  of  dog,  viewed  from  above  and  in  profile.  F,  frontal  fissure,  some- 
times termed  crucial  sulcus,  corresponding  to  the  fissure  of  Rolando  in  man;  S,  fissure  of  Sylvius. 
around  which  the  four  longitudinal  convolutions  are  concentrically  arranged;  1,  flexion  of  head  on 
the  neck,  in  the  median  line;  flexion  of  head  on  the  neck,  witli  rotation  towards  the  side  of  the 
stimulus;  3,  4,  flexiou  and  extension  of  anterior  limb;  5,  <i,  flexion  ami  extension  of  posterior  limb: 
7,  8,  9,  contraction  of  orbicularis  oculi.  and  the  facial  muscles  in  general.  The  unshaded  pari  ifl 
that  exposed  by  opening  the  skull.    (Dalton.) 

of  4,  of  latissimus  dorsi;  of  5,  extension  forward  of  arm;  a,  b,  c,  d, 
movements  of  hand  and  wrist;  of  6.  supination  and  flexion  of  forearm; 
>of  7,  elevation  of  the  upper  lip;  of  8,  conjoint  action  of  elevation  of 


518 


HANDBOOK    OF  PHYSIOLOGY. 


upper  lip  and  depression  of  lower;  of  9,  opening  of  mouth  and  protru> 
sion  of  tongue;  of  10,  retraction  of  tongue;  of  11,  action  of  platysma; 
of  12,  elevation  of  eyebrows  and  eyelids,  dilatation  of  pupils,  and  turn- 
ing head  to  opposite  side;  of  13,  eyes  directed  to  opposite  side  and  up 
wards,  with  usually  contraction  of  the  pupils;  of  13',  similar  action,  but 
eyes  usually  directed  downwards;  of  14,  retraction  of  opposite  ear,  head 
turns  to  the  opposite  side,  the  eyes  widely  opened,  and  pupils  dilated; 
of  15,  stimulation  of  this  region,  which  corresponds  to  the  tip  of  the  un- 
cinate convolution,  causes  torsion  of  the  lip  and  nostril  of  the  same  side. 
It  is  thus  seen  that  the  motor  areas  chiefly  correspond  with  the  as- 
cending frontal  and  ascending  parietal  convolutions,  and  that  the  move- 
ments of  the  leg  are  represented  at  the  upper  part  of  these  convolutions, 


Fig.  356. 


Fig.  357. 


Figs.  356  and  357.— Diagram  of  monkey's  brain  to  show  the  effects  of  electric  stimulation  of  cer- 
tain spots.    (According  to  Ferrier.) 

then  follow  from  above  downwards  the  centres  for  the  arms,  the  face, 
the  lips,  and  the  tongue. 

According  to  the  further  researches  of  Schafer  and  Horsley,  electrical 
stimulation  of  the  marginal  convolution  internally  at  the  parts  corre- 
sponding with  the  ascending  frontal  and  parietal  convolutions,  from 
before  backwards,  produces  movements  of  the  arm,  of  the  trunk,  and 
of  the  leg. 

A  good  deal  of  doubt  was  thrown  upon  the  experiments  of  Ferrier 
by  Goltz  and  other  observers,  from  the  results  of  excising  the  so-called 
motor  areas  of  the  dog's  brain.  It  was  found  that  the  part  might  be 
sliced  away  or  washed  away  with  a  stream  of  water,  but  that  no  perma- 


THE    CEREBROSPINAL    NERVOUS    SYSTEM. 


510 


nent  paralysis  ensued.  Burdon-Sanderson,  too,  showed  that  stimulation 
of  different  points  in  a  horizontal  section,  through  the  deeper  parts  of 
the  hemispheres,  produces  the  same  effects  as  stimulation  of  the  so-called 
"  centres. " 

More  extensive  observations,  however,  have  confirmed  Ferrier's  origi- 
nal statement,  at  any  rate  with  regard  to  the  monkey's  brain.  Destruc- 
tion of  the  motor  areas  for  the  arm  produces  permanent  paralysis  of  the 
arm  of  the  opposite  side,  and  similarly  of  that  for  the  leg,  paralysis  of 
the  opposite  leg.  If  both  areas  are  destroyed  permanent  hemiplegia 
ensues.  Paralysis  of  so  extensive  and  permanent  character  does  not, 
however,  appear  the  rule  when  the  brain  of  a  dog  is  used  instead  of  that 
of  the  monkey.  It  is  suggested  that  in  the  animal  lower  in  the  scale, 
the  functions  which  in  the  monkey  are  discharged  by  the  cortical  centres 
may  be  subserved  by  the  basal  ganglia. 

Motorial  Areas  of  Hie  Human  Brain. — It  is  naturally  of  great  im- 


A.f 


THl 


Fig.  358.— Motorial  areas  of  the  brain.  A.F.,  ascending  frontal  convolution;  A. P.,  ascending 
parietal;  F.R.,  fissure  of  Rolando;  F.  St/.,  sylvian  fissure.    (After  Growers. ) 

portance  to  discover  how  far  the  result  of  experiments  upon  the  dog  and 
monkey  hold  good  with  regard  to  the  human  brain.  Evidence  furnished 
by  diseased  conditions  is  not  wanting  to  support  the  general  idea  of  the 
existence  of  cortical  motorial  centres  in  the  human  brain  (Fig.  358). 

So  far,  however,  it  has  been  possible  to  localize  motor  functions  in 
the  frontal  and  ascending  parietal  convolutions,  only  to  the  convolu- 
tions which  bound  the  fissure  of  Rolando,  and  to  those  on  the  inner  side 
of  the  hemispheres  which  correspond  thereto. 

The  position  of  the  centres  is  probably  much  the  same  as  in  the 
monkey's  brain — those  for  the  leg  above,  those  for  the  arm,  face,  lips, 
and  tongue  from  above  downwards.  Destruction  of  these  parts  causes 
paralysis,  corresponding  to  the  district  affected,  and  irritation  causes 
convulsions  of  the  muscles  of  the  same  part.  Again,  a  number  of  cases 
are  on  record  in  which  aphasia,  or  the  loss  of  power  of  expressing  ideas 


520 


HANDBOOK    OF    PHYSIOLOGY. 


in  words,  has  been  associated  with  disease  of  the  posterior  part  of  the 
lower  or  third  frontal  convolution  on  the  left  side.  This  condition  is 
usually  associated  with  paralysis  of  the  right  side  (right  hemiplegia). 

This  district  of  the  brain  is  now  generally  known  as  the  motor  area; 
and  there  seems  no  doubt  whatever  that  from  this  area  pass  the  nerve- 
fibres  which  proceed  to  the  spinal  cord,  and  are  there  represented  as  the 
pyramidal  tracts. 

This  is  the  reason,  no  doubt,  thau  movements  are  produced  on  stimu- 
lation of  the  white  matter  after  the  superficial  gray  matter  of  the  ani- 
mal's brain  has  been  sliced  off. 

Motor  tracts  in  the  train. — These  motor  fibres  are  connected  with 
the  pyramidal  cells  of  the  cortex,  and  are  indeed  their  continuations. 

It  will  be  necessary,  therefore,  to  trace  them  from  the  cortex  down- 


Fig.  359. 


Fig.  360. 


Fig.  359.— Diagram  to  show  the  connecting  of  the  Frontal  Occipital  Lobes  with  the  Cerebellum, 
etc.  The  dotted  fines  passing  in  the  crusta  (toc),  outside  the  motor  fibres,  indicate  the  connection 
between  the  temporo-occipital  lobe  and  the  cerebellum,  f.c,  the  fronto-cerebellar  fibres,  which 
pass  internally  to  the  motor  tract  in  the  crusta;  i.f.,  fibres  from  the  caudate  nucleus  to  the  pons. 
fe.,  frontal  lobe;  Oc,  occipital  lobe;  af  ,  ascending  frontal;  ap.,  ascending  parietal  convolutions; 
pcf.,  pre-central  fissure  in  front  of  the  ascending  frontal  convolution;  fr.,  fissure  of  Rolando; 
ipf.,  inter-parietal  fissure;  a  section  of  cms  is  lettered  on  the  left  side,  sn.,  substantia  nigra; 
py,  pyramidal  motor  fibre,  which  on  the  right  is  shown  as  continuous  hnes  converging  to  pass 
through  the  posterior  limb  of  ic,  internal  capsule  (the  knee  or  elbow  of  which  is  shown  thus  *) 
upwards  into  the  hemisphere  and  downwards  through  the  pons  to  cross  at  the  medulla  in  the 
anterior  pyramids.    (Gowers.) 

Fig.  360. — Diagram  to  show  the  relative  positions  of  the  several  motor  tracts  in  their  course 
from  the  cortex  to  the  eras.  The  section  through  the  convolutions  is  vertical;  that  through  the 
internal  capsule,  I,  C,  horizontal;  that  through  the  eras  again  vertical.  C,N,  caudate  nucleus ;  O, 
TH,  optic  thalamus,  L2  and  L3,  middle  and  outer  part  of  lenticular  nucleus;  /,  a,  I,  face,  arm, 
and  leg  fibres.    The  words  in  italic  indicate  corresponding  cortical  centres.    ( Gowersj 


wards.  From  the  motor  area  of  the  cortex  they  converge  to  the  internal 
capsule,  a  comparatively  narrow  band  of  fibres  passing  first  of  all  be- 
tween the  two  parts  of  the  corpus  striatum,  namely,  the  intra-ventricu- 
lar  portion,  or  caudate  nucleus,  and  the  extra-ventricular  portion,  or 
lenticular  nucleus,  and  then  between  the  optic  thalamus  internally  and 


THE    CEREBROSPINAL    NERVors    SYSTEM. 


521 


the  lenticular  nucleus  externally  (Fig.  3G0). 
nal  capsule  are  most  important. 


The  relations  of  the  inter- 


Corpora  Striata. — (1.)  The  corpora  striata  are  situated  in  front  of 
the  optic  thalami,  partly  within  and  partly  without  the  lateral  ventricle. 
Each  corpus  striatum  consists  of  two  parts. 

(a.)  An  intra-veutricular  portion  (caudate  nucleus)  which  is  conical 
in  shape,  with  the  base  of  the  cone  forwards;  it  consists  of  gray  matter, 
with  white  substance  in  its  centre,  (b.)  An  extra-ventricular  portion 
(lenticular  nucleus),  which  is  separated  from  the  other  portion  by  a 

layer  of  white  material,  which  forms  a  portion  of  the  internal  capsule, 

the  anterior  limb.  The  lenticular  nucleus  is  seen,  on  a  horizontal  sec- 
tion of  the  hemisphere,  to  consist  of  three  parts,  separated  from  one 
another  by  white  matter,  of  which  the  smallest  is  inside,  each  part  some- 
what resembling  in  shape  a  wedge.  The  upper  and  internal  surface  is 
in  relation  with  the  caudate  nucleus,  being  separated  from  it  by  the  ante- 


C.0, 


VJH 


Fig.  361.— Vertical  section  through  the  cerebrum  and  basic  ganglia  to  show  the  relations  of  the 
latter,  co,  cerebral  convolutions;  c.c,  corpus  callosum;  r.l..  lateral-ventricle;  /,  fornix;  vIIL,  third 
ventricle;  n.c,  caudate  nucleus;  th,  optic  thalamus;  n.L,  lenticular  nucleus:  c.t\,  internal  capsule; 
cl.,  claustrura;  c.e.,  external  capsule;  m,  corpus  mammilla  re;  t.O.,  optic  tract;  s.t.t,  stria  termi- 
nalis;  /(.(».,  nucleus  amygdala?;  cm,  soft  commissure.    (Sehwalbe.  > 

rior  limb  of  the  internal  capsule.  The  remainder  of  the  internal  surface  is 
in  relation  to  the  optic  thalamus,  being  separated  from  it  by  the  posterior 
limb  of  the  internal  capsule.  The  anterior  and  posterior  limbs  of  the 
internal  capsule  meet  at  an  acute  angle,  which  is  known  as  the  Jcnee  of 
the  internal  capsule.  The  horizontal  section  is  wider  in  the  centre 
than  at  the  end.  On  the  outside  is  the  gray  lamina  (clau strum)  sepa- 
rated by  a  thin  white  layer — external  capsule — from  the  lenticular 
nucleus. 

Optic  Thalami. — (2.)  The  Optic  Thalami  are  oval  in  shape,  and 
rest  upon  the  crura  cerebri.  The  upper  surface  of  each  thalamus  is 
free,  and  of  white  substance,  it  projects  into  the  lateral  ventricle.  The 
posterior  surface  is  also  white.  The  inner  sides  of  the  two  optic  thalami 
are  in  partial  contact,  and  are  composed  of  gray  material  uncovered  by 
white,  and  are.  as  a  rule,  connected  together  by  a  transverse  portion. 


522  HANDBOOK    OF    PHYSIOLOGY. 

In  the  internal  capsule  the  fibres  which  pass  onwards  and  downwards 
to  the  pyramidal  tracts  of  the  spinal  cord  do  not  occupy  more  than  a 
small  section,  namely,  that  part  known  as  the  knee,  and  the  anterior 
two-thirds  of  the  posterior  segment  (Fig.  360).  In  this  district  the 
fibres  for  the  face,  arm,  and  leg,  are  in  this  relation:  those  for  the  face 
and  tongue  are  just  at  the  knee,  and  below  or  behind  them  come  first  the 
fibres  for  the  arm  and  then  those  for  the  leg.  The  posterior  third  of  the 
posterior  segment  is  occupied  by  the  sensory  fibres. 

Following  the  fibres  downwards  from  the  internal  capsule  it  is  found 
that  those  which  are  motor  in  function  descend  in  the  crusta  of  the  crus 
on  either  side,  where  they  are  collected  into  the  upper  part  of  the  mid- . 
die  third,  and  that  they  then  pass  through  the  pons  to  form  the  anterior 
pyramids  of  the  medulla.  The  fibres  then  either  decussate  in  the 
middle  line,  passing  over  to  the  opposite  side  to  become  the  lateral  or 
crossed  pyramidal  tract  of  the  lateral  column  of  the  cord,  or  remain  as 
the  direct  pyramidal  tract  of  the  anterior  column  on  either  side  of  the 
anterior  fissure.  The  direct  pyramidal  tracts,  it  will  be  remembered, 
decussate  by  degrees  in  the  cord. 

This  pathway  of  the  pyramidal  fibres  is  demonstrated  by  their  degen- 
eration when  any  lesion  separates  the  fibres  from  their  corresponding 
cortical  cells,  as,  for  example,  a  hemorrhage  into  the  corpus  striatum  of 
sufficient  extent — but  the  interruption  may  take  place  anywhere  in  the 
whole  course  of  the  tract.  If  the  whole  of  these  fibres  on  one  side  is 
destroyed  transversely,  above  the  decussation,  hemiplegia  of  the  opposite 
side,  more  or  less  complete,  results.  The  idea  which  was  formerly  held, 
that  some  of  these  fibres  pass  through  the  corpus  striatum  does  not 
appear  to  be  supported  by  sufficient  evidence.  They  have  an  interrupted 
course.  The  reason  why  a  hemorrhage  into  the  corpus  striatum  pro- 
duces hemiplegia  appears  to  be  because  of  the  almost  certain  pressure 
which  such  a  lesion  exerts  upon  the  fibres  of  the  internal  capsule. 

Sensory  paths  in  the  train. — The  knowledge  which  we  possess  of  the 
distribution  of  the  sensory  fibres  in  the  brain  is  not  nearly  so  definite  as 
that  which  has  been  obtained  of  the  motor  tracts.  As  we  have  seen,  the 
course  of  the  sensory  fibres  even  in  the  cord  is  not  by  any  means  com- 
pletely understood.  Supposing  such  fibres  to  be  contained  chiefly  in  the 
anterior  part  of  the  lateral  columns  and  in  the  posterior  columns  of  the 
cord,  having  previously  crossed  over  to  the  opposite  side  of  the  cord  to 
that  from  whence  they  came,  they  probably  proceed  in  the  posterior  half 
of  the  medulla,  chiefly  in  the  formatio  reticularis,  and  in  the  correspond- 
ing part  of  the  pons,  beneath  the  corpora  quadrigemina  to  the  tegmen- 
tum of  the  crus.  In  this  they  pass  above  the  locus  niger,  and  enter  the 
posterior  third  of  the  posterior  limb  of  the  internal  capsule  [sensory 
crossiuay).  From  this  district  the  fibres  pass  on  into  the  white  matter 
of  the  brain  and  probably  extend  into  the  so-called  motorial  areas  already 


THE    CKKKBRO-SPINAL    NERVOUS    SYSTEM.  523 

spoken  of  situated  in  the  posterior  frontal  and  anterior  parietal  regions. 
Some  of  the  fibres  pass  into  the  optic  thalamus.  The  fibres  of  the  fifth 
nerve  join  the  tegmentum,  and  so  in  the  internal  capsule  are  included 
with  the  other  sensory  fibres.  This  is  also  probably  the  case  with  the 
other  nerves  of  special  sense, — smell,  vision,  and  hearing. 

Cerebro-cerebellar  fibres. — The  tracts  of  fibres  connecting  the  cere- 
bellum with  the  cerebrum  are  in  all  probability  at  least  three  in  number. 
(a.)  Fibres  situated  in  the  crusta  to  the  inside  of  the  pyramidal  fibres 
(Fig.  360).  These  pass  upwards  in  the  anterior  limb  of  the  internal 
capsule  and  proceed  into  the  anterior  frontal  lobes.  In  the  other  direc- 
tion they  descend  to  the  pons,  and  appear  to  end  in  the  gray  matter 
within  it.  But  it  is  very  likely  that  from  this  gray  matter  fibres  pro- 
ceed, to  the  lateral  and  posterior  parts  of  the  opposite  side  of  the 
cerebellum.  As  the  fibres  degenerate  downwards  they  conduct  in  the 
same  direction,  but  are  arrested  at  the  pons,  where  they  are  interrupted 
by  graJ  matter,  (b.)  Fibres  which  in  the  crusta  are  situated  outside 
the  pyramidal  tract  do  not  enter  the  internal  capsule,  but  at  once  pro- 
ceed to  the  occipital  and  temporo-sphenoidal  lobes.  These  fibres  pro- 
ceed downwards  to  the  cerebellum,  being  interrupted  in  the  pons,  and 
from  thence  proceed  to  the  upper  surface  of  the  opposite  side  of  the 
cerebellum  near  the  middle  lobe,  (c.)  The  third  tract  is  situated  (Fig. 
359,  i,  f)  beneath  the  pyramidal  fibres  and  above  the  locus  niger.  The 
fibres  pass  from  the  corpus  striatum  chiefly  from  the  caudate  nucleus  to 
the  pons  and  thence  to  the  cerebellum. 

Functions  of  the  Corpora  Striata. — The  idea  that  the  corpora  striata 
are  concerned  in  the  transmission  of  motor  impulses,  or  that  they  are 
the  great  motor  ganglia  at  the  base  of  the  brain,  rests  upon  insufficient 
evidence.  It  has  been  already  incidentally  mentioned  that  lesions  of  the 
corpora  striata  produce  hemiplegia  only  because  of  the  pressure  effects 
they  exercise  upon  the  internal  capsule  close  by. 

The  caudate  nucleus  is  connected  with  the  opposite  side  of  the  cere- 
bellum by  fibres  which  conduct  downwards,  and  the  lenticular  nucleus 
is  connected  with  the  cerebellum  by  fibres  from  the  tegmentum  and  supe- 
rior cerebellar  peduncles  which  conduct  upwards.  It  is  suggested  that  the 
corpora  striata  are  central  organs  analogous  to  the  cerebral  cortex  itself. 
"The  analogy  to  those  parts  of  the  cortex  that  are  connected  with  the 
cerebellum  is  rendered  still  greater  by  the  fact  that  a  lesion,  even  an  ex- 
tensive lesion,  may  exist  in  either  the  caudate  or  lenticular  nucleus,  and 
so  long  as  it  does  not  interfere  with  the  functions  of  the  motor  or  sen- 
sory parts  of  the  internal  capsules  it  causes  no  persistent  symptoms." 
(Gowers.) 

Functions  of  the  optic  thalami. — That  the  optic  thalami  are  the  great 
sensory  centres  at  the  base  of  ihe  brain — which  was  a  view  held  by  many 
until  recently — does  not  seem  to  to  based  upon  sufficiently  accurate  ob- 


.524 


HANDBOOK    OF    PHYSIOLOGY. 


servations.  Some  fibres  from  the  tegmentum  enter  it  no  doubt,  but  the 
main  body  skirts  the  ganglion  on  either  side,  and  does  not  enter  it. 
Fibres  connect  the  optic  thalamus  with  the  superior  peduncle  of  the 
cerebellum  of  the  opposite  side.  Fibres  connect  it  with  the  optic  nerves. 
From  the  optic  thalamus  of  either  side  fibres  pass  to  the  lenticular 
nucleus  as  well  as  to  all  parts  of  the  cerebral  cortex. 

Lesions  of  the  optic  thalamus  do  not  of  themselves  produce  loss  of 
sensation.  If  such  a  symptom  follows,  it  is  due  to  pressure  upon,  or 
injury  to  the  posterior  limb  of  the  internal  capsule.  The  optic  thalamus 
is  connected  with  visual  sensations,  and  may  be  a  reflex-centre  for  some 
of  the  higher  reflex  actions. 

Of  the  functions  of  the  external  capsule  and  of  the  claustrum 
nothing  definite  is  known. 


The  Cerebellum. 

The  Cerebellum  (7,  8,  9,  10,  Fig.  341),  is  composed  of  an  elongated 
central  or  lobe  portion,  called  the  vermiform  processes,  and  two  hemi- 
spheres.    Each  hemisphere   is   connected  with  its  fellow,  not  only  by 


FlG.  363.— Cerebellum  in  section  and  fourth  ventricle,  with  the  neighboring  parts.  1,  median 
groove  of  fourth  ventricle,  ending  below  in  the  calamus  scriptorius,  with  the  longitudinal  emi- 
nences formed  by  the  fasciculi  teretes,  one  on  each  side;  2,  the  same  groove,  at  the  place  where 
the  white  streaks  of  the  auditory  nerve  emerge  from  it  to  cross  the  floor  of  tbe  ventricle;  3, 
inferior  crus  or  peduncle  of  the  cerebellum,  formed  by  the  restiform  body;  4,  posterior  pyramid ; 
above  this  is  the  calamus  scriptorius;  5,  superior  crus  of  cerebellum,  or  processus  e  cerebello  ad 
cerebrum  Cor  ad  testes;;  6,  6,  fillet  to  the  side  of  the  crura  cerebri;  7,  7,  lateral  grooves  of  the 
crura  cerebri;  8,  corpora  quadrigemina.     (From  Sappey  after  Hirschfeld  and  Leveifle .) 

means  of  the  vermiform  processes,  but  also  by  a  bundle  of  fibres  called 
the  middle  crus  or  peduncle  (the  latter  forming  the  greater  part  of  the 
pons  Varolii),  while  the  superior  crura  with  the  valve  of  Vieussens  con- 
nect it  with  the  cerebrum  (5,  Fig.  3G1),  and  the  inferior  crura  (formed 
by  the  prolonged  restiform  bodies)  connect  it  with  the  medulla  oblon- 
gata (3,  Fig.  361). 


THE    CEREBROSPINAL    NERVOUS    SYSTEM.  525 

Structure. — The  cerebellum  is  composed  of  white  and  gray  matter, 
the  latter  being  external,  like  that  of  the  cerebrum,  and  like  it,  infolded, 
so  that  a  larger  area  may  be  contained  in  a  given  space.  The  convolu- 
tions of  the  gray  matter,  however,  are  arranged  after  a  different  pattern  as 
shown  in  Fig.  302.  Besides  the  gray  substance  on  the  surface,  there  is, 
near  the  centre  of  the  white  substance  of  each  hemisphere,  a  small  cap- 
sule of  gray  matter  called  the  corjyus  dentatum  (Fig.  363,  cd),  resembling 
very  closely  the  corpus  dentatum  of  the  olivary  body  of  the  medulla  ob- 
longata (Fig.  363.  o). 

If  a  section  be  taken  through  the  cortical  portion  of  the  cerebellum, 
the  following  distinct  layers  can  be  seen  (Fig.  364)  by  microscopic  exami- 
nation. 

(1.)  Immediately  beneath  the  pia  mater  (p  m)  is  a  layer  of  considera- 
ble thickness,  which  consists  of  a  delicate  connective  tissue,  in  which  are 
scattered  several  spherical  corpuscles  like  those  of  the  granular  layer  of 
the  retina,  and  also  an  immense  number  of  delicate  fibres  passing  up 


Fig.  363.— Outline  sketch  of  a  section  of  the  cerebellum,  showing  the  corpus  dentatum.  The 
section  has  been  carried  through  the  left  lateral  part  of  the  pons,  so  as  to  divide  the  superior  pe- 
duncle and  pass  nearly  through  the  middle  of  the  left  cerebellar  hemisphere.  The  olivary  body  has 
also  been  divided  longitudinally  so  as  to  expose  in  section  its  corpus  dentatum.  c  r,  eras  cerebri; 
/,  fillet;  q,  corpora  quadrigemina;  sp,  superior  peduncle  of  the  cerebellum  divided;  m  p.  middle  pe- 
duncle or  lateral  part  of  the  pons  Varolii,  with  fibres  passing  from  it  into  the  white  stem :  a  r.  » in- 
tinuation  of  the  white  stem  radiating  towards  the  arbor  vitae  of  the  folia;  c  d,  corpus  dentatum;  o, 
olivary  body  with  its  corpus  dentatum ;  p,  anterior  pyramid.    (Allen  Thomson. 

towards  the  free  surface  and  branching  as  they  go.  These  fibres  are  the 
processes  of  the  cells  of  Purkinje.  (2.)  The  Cells  of  Purkitijc  (p). 
These  are  a  single  layer  of  branched  nerve-cells,  which  give  off  a  single 
unbranched  process  downwards,  and  numerous  processes  up  into  the  ex- 
ternal layer,  some  of  which  become  continuous  with  the  scattered  cor- 
puscles. (3.)  The  granular  layer  (g),  consisting  of  immense  numbers 
of  corpuscles  closely  resembling  those  of  the  nuclear  layers  of  the  retina. 
(4.)  Xerve-fibre  layer  (/).  Bundles  of  nerve-fibres  forming  the  white 
matter  of  the  cerebellum,  which,  from  its  branched  appearance  has  been 
named  the  "arbor  vita\" 

Functions. — The  physiology  of  the  Cerebellum  may  be  considered  in 
its  relation  to  sensation,  voluntary  motion,  and  the  instincts  or  higher 
faculties  of  the  mind.     Its  supposed  functions,  like  those  of  every  other 


526 


HANDBOOK    OF    PHYSIOLOGY, 


part  of  the  nervous  system,  have  been  determined  by  physiological  ex- 
periment, by  pathological  observation,  and  by  its  comparative  anatomy. 
(1.)  With  the  exception  of  its  middle  lobe,  it  is  itself  insensible  to 
irritation,  and  may  be  all  cut  away  without  eliciting  signs  of  pain 
(Longet).     Its  removal  or  disorganization  by  disease  is  also  generally  un- 


-JX;    £«v 


Fig.  364.— Vertical  section  of  dog's  cerebellum;  p  m,  pia  mater;  p,  corpuscles  of  Purkinje,  which 
are  branched  nerve-cells  lying  in  a  single  layer  and  sending  single  processes  downwards  and  more 
numerous  ones  upwards,  which  branch  continuously  and  extend  through  the  deep  "molecular 
layer  ' '  towards  the  free  surface ;  g,  dense  layer  of  ganglionic  corpuscles,  closely  resembling  nuclear 
layers  of  retina;  /,  layer  of  nerve-fibres,  with  a  few  scattered  ganglionic  corpuscles.  This  last  layer 
iff)  constitutes  part  of  the  white  matter  of  the  cerebellum,  while  the  layers  between  it  and  the 
free  surface  are  gray  matter.    (Klein  and  Noble  Smith.) 

accompanied  by  loss  or  disorder  of  sensibility;  animals  from  which  it  is 
removed  can  smell,  see,  hear,  and  feel  pain,  to  all  appearance,  as  per- 
fectly as  before  (Flourens ;    Magendie).     Yet,  if  any  of  its  crura   be 


THE   CEREBROSPINAL    NERVOUS    SYSTEM.  ~fj~ 

touched,  pain  is  indicated;  and,  if  the  restiform  tracts  of  the  medulla 
oblongata  be  irritated,  the  most  acute  suffering  appears  to  be  produced. 
It  cannot,  therefore,  be  regarded  as  a  principal  organ  of  sensation. 

(2.)  Co-ordination  of  Movements. — In  reference  to  motion,  the  ex- 
periments of  Longet  and  many  others  agree  that  no  irritation  of  the 
cerebellum  produces  movement  of  any  kind.  Kemarkable  results,  how- 
ever, are  produced  by  removing  parts  of  its  substance.  Flourens  (whose 
experiments  have  been  confirmed  by  those  of  Bouillaud,  Longet,  and 
others)  extirpated  the  cerebellum  in  birds  by  successive  layers.  Feeble- 
ness and  want  of  harmony  of  muscular  movements  were  the  consequence 
of  removing  the  superficial  layers.  When  he  reached  the  middle  layers, 
the  animals  became  restless  without  being  convulsed;  their  movements 
were  violent  and  irregular,  but  their  sight  and  hearing  were  perfect.  By 
the  time  that  the  last  portion  of  the  organ  was  cut  away,  the  animals  had 
entirely  lost  the  powers  of  springing,  flying,  walking,  standing,  and  pre- 
serving their  equilibrium.  When  an  animal  in  this  state  was  laid  upon 
its  back,  it  could  not  recover  its  former  posture,  but  it  fluttered  its  wings, 
and  did  not  lie  in  a  state  of  stupor;  it  saw  the  blow  that  threatened  it, 
and  endeavored  to  avoid  it.  Volition  and  sensation,  therefore,  were  not 
lost,  but  merely  the  faculty  of  combining  the  actions  of  the  muscles; 
and  the  endeavors  of  the  animal  to  maintain  its  balance  were  like  those 
of  a  drunken  man. 

The  experiments  afforded  the  same  results  when  repeated  on  all 
classes  of  animals;  and  from  them  and  the  others  before  referred  to, 
Flourens  inferred  that  the  cerebellum  belongs  neither  to  the  sensory  nor 
the  intellectual  apparatus;  and  that  it  is  not  the  source  of  voluntary 
movements,  although  it  belongs  to  the  motor  apparatus;  but  is  the  organ 
for  the  co-ordiuation  of  the  voluntary  movements,  or  for  the  excitement 
of  the  combined  action  of  muscles. 

Such  evidence  as  can  be  obtained  from  cases  of  disease  of  this  organ 
confirms  the  view  taken  by  Flourens;  and,  on  the  whole,  it  gains  sup- 
port from  comparative  anatomy;  animals  whose  natural  movements  re- 
quire most  frequent  and  exact  combinations  of  muscular  actions  being 
those  whose  cerebellaare  most  developed  in  proportion  to  the  spinal  cord. 

We  must  remember,  too,  that  the  cerebellum  is  connected  with  the 
posterior  columns  of  the  cord  as  well  as  with  the  direct  cerebellar  tract. 
both  of  which  probably  convey  to  the  middle  lobe  muscular  sensations. 
It  is  also  connected  with  the  auditory  nerves.  Movements  of  the  eyes 
also  occur  on  direct  stimulation  of  the  middle  lobe.  It  seems,  therefore, 
to  be  connected  in  some  way  with  all  of  the  chief  sensory  impulses  which 
have  to  do  with  the  maintenance  of  the  equilibrium. 

Foville  supposed  that  the  cerebellum  is  the  organ  of  muscular  s< 
i.  e.,  the  organ  by  which  the  mind  acquires  that  knowledge  of  the  actual 
state  and  position  of  the  muscles  which  is  essential  to  the  exercise  of  the 


528  HANDBOOK    OF    PHYSIOLOGY. 

will  upon  them;  and  it  must  be  admitted  that  all  the  facts  just  referred 
to  are  as  well  explained  on  this  hypothesis  as  on  that  of  the  cerebellum 
being  the  organ  for  combining  movements.  A  harmonious  combination 
of  muscular  actions  must  depend  as  much  on  the  capability  of  appreciat- 
ing the  condition  of  the  muscles  with  regard  to  their  tension,  and  to  the 
force  with  which  they  are  contracting,  as  on  the  power  which  any  special 
nerve-centre  may  possess  of  exciting  them  to  contraction.  And  it  is  be- 
cause the  power  of  such  harmonious  movement  would  be  equally  lost, 
whether  the  injury  to  the  cerebellum  involved  injury  to  the  seat  of  mus- 
cular sense,  or  to  the  centre  for  combining  muscular  actions,  that  ex- 
periments on  the  subject  afford  no  proof  in  one  direction  more  than  the 
other. 

Forced  Movements. — The  influence  of  each  half  of  the  cerebellum 
is  directed  to  muscles  on  the  opposite  side  of  the  body;  and  it  would  ap- 
pear that  for  the  right  ordering  of  movements,  the  actions  of  its  two 
halves  must  be  always  mutually  balanced  and  adjusted.  For  if  one  of 
its  crura,  or  if  the  pons  on  either  side  of  the  middle  line,  be  divided,  so 
as  to  cut  off  from  the  medulla  oblongata  and  spinal  cord  the  influence  of 
one  of  the  hemispheres  of  the  cerebellum,  strangely  disordered  move- 
ments ensue  (forced  movements).  The  animals  fall  down  on  the  side 
opposite  to  that  on  which  the  crus  cerebelli  has  been  divided,  and  then 
roll  over  continuously  and  repeatedly;  the  rotation  being  always  round 
the  long  axis  of  their  bodies,  and  generally  from  the  side  on  which  the 
injury  has  been  inflicted.  The  rotations  sometimes  take  place  with  much 
rapidity;  as  often,  according  to  Magendie,  as  sixty  times  in  a  minute, 
and  may  last  for  several  days.  Similar  movements  have  been  observed 
in  men;  as  by  Serres  in  a  man  in  whom  there  was  apoplectic  effusion  in 
the  right  crus  cerrebelli;  and  by  Bellhomme  in  a  woman,  in  whom  an 
exostosis  pressed  on  the  left  crus.  They  may,  perhaps,  be  explained  by 
assuming  that  the  division  or  injury  of  the  crus  cerebelli  produces  para- 
lysis or  imperfect  and  disorderly  movements  of  the  opposite  side  of  the 
body;  the  animal  falls,  and  then,  struggling  with  the  disordered  side  on 
the  ground,  and  striving  to  rise  with  the  other,  pushes  itself  over;  and 
so  again  and  again,  with  the  same  act,  rotates  itself.  Such  movements 
cease  when  the  other  crus  cerebelli  is  divided;  but  probably  only  because 
the  paralysis  of  the  body  is  thus  made  almost  complete.  Other  varieties 
of  forced  movements  have  been  observed,  especially  those  named  "cir- 
cus movements,"  when  the  animal  operated  upon  moves  round  and 
round  in  a  circle;  and  again  those  in  which  the  animal  turns  over  and 
over  in  a  series  of  somersaults.  Nearly  all  these  movements  may  result 
on  section  of  one  or  other  of  the  following  parts;  viz.  crura  cerebri,  me- 
dulla, pons,  cerebellum,  corpora  quadrigemina,  corpora  striata,  optic 
thalami,  and  even,  it  is  said,  of  the  cerebral  hemispheres. 


THE    CEREBROSPINAL    NKUVolS    SYSTEM.  52  I 

Sensory  Centres  in  the  Cerebral  Cortex. 

Experimental  lesions  of  various  portions  of  the  cerebral  cortex  and 
stimulation  of  such  parts  appears  to  show  that  the  special  senses  are  in 
some  way  represented  at  definite  spots  in  the  convolutions. 

Thus  (a)  the  visual  or  optic  centre  is  localized  in  the  occipital  lobe  on 
either  side  on  the  outer  convex  part  (Fig.  358).  This  has  been  demon- 
strated in  the  dog's  brain  by  Munk.  In  the  human  brain  there  seems 
to  be  a  very  complex  mechanism  about  this  centre.  The  optic  nerve- 
fibres  having  partially  decussated.in  the  chiasma  pass  in  the  optic  tract 
to  the  optic  thalanii,  and  thence  to  the  cortical  substance  of  the  occipi- 
tal lobe.  Ilemianopia,  restriction  of  the  field  of  vision  of  opposite  sides 
of  the  two  eyes,  may  be  produced,  either  by  a  lesion  of  one  optic  tract, 
in  which  are  (chiefly)  the  crossed  fibres  from  the  nasal  portion  of  the 
retina  of  the  opposite  eye  and  the  uncrossed  fibres  of  the  external  por- 
tion of  the  retina  of  the  corresponding  eye;  or  of  the  occipital  centre. 
Part  of  the  fibres  of  the  optic  tract  pass  to  the  corpora  geniculata  and 
to  the  corpora  quadrigemina.  Each  of  these  so-called  half-vision  cen- 
tres of  opposite  sides,  situated  in  the  occipital  lobes,  appears  to  be  in 
connection  with  a  higher  centre  in  which  the  retinae  of  both  eyes  are 
represented,  but  especially  that  of  the  opposite  eye..  If  both  occipital 
lobes  be  extensively  diseased  total  blindness  results. 

(b)  The  Olfactory  centre,  is  said  to  be  localized  in  the  anterior  ex- 
tremity of  the  uncinate  gyrus.  The  fibres,  however,  appear  to  be  con- 
nected with  a  centre  on  the  same  side;  others  cross  over  to  a  centre  on 
the  opposite  side. 

(c)  The  A  uditory  centre,  is  situated  (according  to  Eerrier  and  Munk) 
in  the  monkey's  brain  in  the  first  temporo-sphenoidal  convolution.  The 
auditory  fibres  pass  up  the  pons  in  which  they  cross,  and  then  in  the 
superior  portion  of  the  tegmentum  through  the  hinder  portion  of  the 
internal  capsule  to  this  centre.  Destruction  of  the  entire  region  causes 
deafness  of  the  opposite  ear. 

(d)  The  centre  for  Taste  has  not  yet  been  localized.  According  to 
Growers,  it  is  quite  probable  that  the  whole  of  the  taste-fibres  belong  to 
the  fifth  nerve.  Those  which  are  distributed  to  the  anterior  parts  of  the 
tongue  in  the  chorda  tympani,  coming  from  that  nerve  through  the  Vid- 
ian, which  passes  from  the  spheno-palatine  ganglion  to  the  facial,  and 
those  which  are  distributed  to  the  back  of  the  tongue  through  the  glosso- 
pharyngeal, being  derived  from  the  otic  ganglion  of  the  fifth  nerve 
through  the  small  petrosal  nerve  and  the  tympanic  plexus. 

34 


CHAPTER   XIX. 

PHYSIOLOGY  OF  THE  CRANIAL  NERVES. 

The  Cranial  nerves  are  commonly  enumerated  as  nine  pairs;  but 
the  number  is  in  reality  twelve  pairs,  the  seventh  nerve  consisting  as  it 
does,  of  two  nerves,  and  the  eighth  of  three.  All  arise  (superficial  ori- 
gin) from  the  base  of  the  encephalon,  in  a  double  series  which  extends 
from  the  under  surface  of  the  anterior  cerebral  lobes  to  the  lower  end 
of  the  medulla  oblongata.  Traced  into  the  substance  of  the  brain  and 
medulla,  the  roots  of  the  nerves  are  found  to  take  origin  from  various 


Fig.  365.— Fourth  ventricle,  with  the  medulla  oblongata  and  the  corpora  quadngemuia.  The 
roman  numbers  indicate  superficial  origins  of  the  cranial  nerves,  while  the  other  numbers  indicate 
their  deep  origins,  or  the  position  of  their  central  nuclei.  8,  8',  8",  8'",  auditory  nuclei  nerves;  t, 
funiculus  teres;  A,  B,  corpora  quadrigemina;  c  g,  corpus  geniculatum;  p,  c,  pedunculus  cerebri;  m, 
c,  p,  middle  cerebellar  peduncle;  s,  c,  p,  superior  cerebellar  peduncle;  i,  c,  p,  inferior  cerebellar  pe- 
duncle; I,  c,  locus  cseruleus;  e,  t,  eminentia  teres;  a,  c,  ala  cinerea;  a,  n,  accessory  nucleus;  o,  obex; 
c,  clava;  /,  c,  funiculus  cuneatus;  /,  g,  funiculus  gracilis. 

masses  of  gray  matter,  which  are  all  connected  one  with  another,  and 
with  the  cerebral  hemispheres. 

The  roots  of  the  olfactory  and  of  the  optic  nerves  have  been  already 
mentioned.  The  third  and  fourth  nerves  arise  from  gray  matter  be- 
neath the  corpora  quadrigemina;  and  the  roots  of  origin  of  the  remainder 
of  the  cranial  nerves  can  be  traced  to  gray  matter  in  the   medulla  oblon- 


PHYSIOLOGY    OF    T1IK    CRANIAL    NERVES. 


531 


gata  in  the  floor  of  the  fourth  ventricle,  and  in  the  more  central  part  of 
the  medulla,  around  its  central  canal,  as  low  down  as  the  decussation  of 
the  pyramids. 

According  to  their  several  functions,  the  cranial  nerves  may  be  thus 
arranged: — 
A.  Nerves  of  special  sense, 


B.  Nerves  of  common  sensation, 


Olfactory,  Optic,  Auditory, 
part  of  the  Glosso-pharyn- 
geal,  and  part  of  the  Fifth. 

The  greater  portion  of  the 
Fifth. 

0.  Nerves  of  motion, Third,  Fourth,  lesser  division 

of  the  Fifth,  Sixth,  Facial, 
and  Hypoglossal. 

D.  Mixed  nerves, Glosso-pharyngeal,  Vagus,  and 

Spinal  accessory. 

The  physiology  of  the  First,  Second,  and  Eighth  will  be  considered 
with  the  organs  of  Special  sense. 


The  Third  Nerve,  or  Motor  Oculi. 

Functions. — The  Third  nerve,  or  motor  oculi,  which  arises  in  three 
distinct  bands  of  fibres  from  the  gray  matter  beneath  the  aqueduct  of 


a,   4 


Fig.  366.— Diagram  of  a  longitudinal  section  through  the  pons,  showing  the  relation  of  the 
nuclei  for  the  ocular  muscles,  co,,  corpora  quadrigemina;  3,  third  nerve;  in.,  its  nucleus;  4,  fourth 
nerve;  iv.,  its  nucleus,  the  posterior  part  of  the  third;  6,  sixth  nerve.  The  probable  position  of  the 
centre  and  nerve  ribres  for  accommodation  is  shown  at  a  and  «';  for  the  reflex  action  of  iris,  at  6, 
and  6';  for  the  external  rectus  muscles,  at  c,  c'.  The  lines  beneath  the  floor  of  the  fourth  ven- 
tricle indicate  fibres,  which  connect  the  nuclei.    (Gowers.) 

Sylvius  near  the  middle  line  in  conjunction  with  the  fourth  nerve.  It 
supplies  the  levator  palpebras  superioris  muscle,  and  all  of  the  muscles 
of  the  eye-ball,  but  the  superior  oblique,  to  which  the  fourth  nerve  is 
appropriated,  and  the  rectus  externus  which  receives  the  sixth  nerve. 
Through  the  medium  of  the  ophthalmic  or  lenticular  ganglion,  of  which 
it  forms  what  is  called  the  short  root,  it  also  supplies  motor  filaments 
to  the  iris  and  ciliary  muscle.  The  fibres  which  subserve  the  three 
functions,  accommodation,  contraction  of  the  pupil,  and  nerve-supply 
to  the  external  ocular  muscles,  arise  from  three  distinct  groups  of  colls. 

When  the  third  nerve  is  irritated  within  the  skull,  all  those  muscles 
to  which  it  is  distributed  are  convulsed.  When  it  is  paralyzed  or  di- 
vided the  following  effects  ensue: — (1)  the  upper  eyelid  can  be  no  longer 


532  HANDBOOK    OF   PHTSIOLOG-Y. 

raised  by  the  levator  palpebral,  but  droops  (ptosis)  and  remains  gently- 
closed  over  tbe  eye,,  under  the  unbalanced  influence  of  the  orbicularis 
palpebrarum,  which  is  supplied  by  the  facial  nerve: — (2)  the  eye  is 
turned  outwards  (external  strabismus)  by  the  unbalanced  action  of  the 
rectus  externus,  to  which  the  sixth  nerve  is  appropriated:  and  hence, 
from  the  irregularity  of  the  axes  of  the  eyes,  double  sight,  diplopia,  is 
often  experienced  when  a  single  object  is  within  view  of  both  the  eyes: 

(3)  the  eye  cannot  be  moved  either  upwards,  downwards,   or  imvards: 

(4)  the  pupil  becomes  dilated  (mydriasis),  and  insensible  to  light:  (o)  the 
eye  cannot  accommodate  for  short  distances. 

Contraction  and  Dilatation  of  the  Pupil. — The  relation  of  the  third 
nerve  to  the  muscles  of  the  iris  is  of  peculiar  interest.  Under  ordinary 
circumstances  the  contraction  of  the  iris  is  a  reflex  action,  which  is  pro- 
duced by  the  stimulus  of  light  on  the  retina  which  is  conveyed  by  the 
optic  nerve  to  the  brain  (probably  to  the  corpora  quadrigemina  or  me- 
dulla), and  thence  reflected  through  the  third  nerve  to  the  iris.  Hence 
the  iris  ceases  to  act  when  either  the  optic  or  the  third  nerve  is  divided 
or  destroyed,  or  when  the  centre  is  destroyed  or  much  compressed.  But 
when  the  optic  nerve  is  divided,  the  contraction  of  the  iris  may  be  ex- 
cited by  irritating  that  portion  of  the  nerve  which  is  connected  with  the 
brain;  and  when  the  third  nerve  is  divided,  the  irritation  of  its  distal 
portion  will  still  excite  the  contraction  of  the  iris. 

The  contraction  of  the  iris  thus  shows  all  the  characters  of  a  reflex 
act,  and  in  ordinary  cases  requires  the  concurrent  action  of  the  optic 
nerve,  its  centre,  and  the  third  nerve;  and,  probably  also,  considering 
the  peculiarities  of  its  perfect  mode  of  action,  of  the  ophthalmic  gan- 
glion. But,  besides,  both  irides  will  contract  under  the  reflected  stimu- 
lus of  light  falling  upon  one  retina  or  under  irritation  of  one  optic  nerve 
only.  Thus  in  amaurosis  of  one  eye,  its  pupil  may  contract  when  the 
other  eye  is  exposed  to  a  stronger  light;  and  generally  the  contraction  of 
each  of  the  pupils  appears  to  be  in  direct  proportion  to  the  total  quan- 
tity of  light  which  stimulates  either  one  or  both  retina?,  according  as 
one  or  both  eyes  are  open. 

The  iris  acts  also  in  association  with  certain  other  muscles  supplied 
by  the  third  nerve:  thus,  when  the  eye  is  directed  inwards,  or  upwards 
and  inwards,  by  the  action  of  the  third  nerve  distributed  in  the  rectus 
internus  and  rectus  superior,  the  iris  contracts,  as  if  under  direct  volun- 
tary influence.  The  will  cannot,  however,  act  on  the  iris  alone  through 
the  third  nerve;  but  this  aptness  to  contract  in  association  with  the  other 
muscles  supplied  by  the  third,  may  be  sufficient  to  make  it  act  even  in 
total  blindness  and  insensibility  of  the  retina,  whenever  these  muscles 
are  contracted.  The  contraction  of  the  pupils,  when  the  eyes  are  moved 
inwards,  as  in  looking  at  a  near  object,  has  probably  the  purpose  of  ex- 
cluding those  outermost  rays  of  light  which  would  be  too  far  divergent 


PHYSIOLOGY   OF   THE   CRANIAL  NERVES.  533 

to  be  refracted  to  a  clear  image  011  the  retina;  and  the  dilatation  in  look- 
ing straight  forwards,  as  in  looking  at  a  distant  object,  permits  the  ad- 
mission of  the  largest  number  of  rays,  of  which  none  are  too  divergent 
to  be  so  refracted. 

The  Fourth  Nerve,  or  Trochlearis. 

Functions. — The  Fourth  nerve,  Nervus  trochlearis,  or  Patheticus, 
is  exclusively  motor,  and  supplies  only  the  trochlearis  or  obliquus  supe- 
rior muscle  of  the  eyeball.  It  arises  from  above  the  fourth  ventricle  from 
the  valve  of  Vieussens,  but  its  fibres  can  be  traced  to  the  lower  part  of 
the  nucleus  of  the  third  (Fig.  366)  nerve.  It  decussates  with  its  fellow 
between  its  deep  and  superficial  origins. 

The  Fifth  Nerve,  or  Trigeminus. 

Functions. — The  Fifth  or  Trigeminal  nerve  resembles,  as  already 
stated,  the  spinal  nerves,  in  that  its  branches  are  derived  through  two 
roots;  namely,  the  larger  or  sensory,  in  connection  with  which  is  the 
Gasserian  ganglion,  and  the  smaller  or  motor  root,  which  has  no  gan- 
glion, and  which  passes  under  the  ganglion  of  the  sensory  root  to  join 
the  third  branch  or  division  which  ensues  from  it.  The  fibres  of  origin 
of  the  fifth  nerve  appear  to  come  from  under  the  floor  of  the  fourth  ven- 
tricle. The  motor  root  to  the  inside  of  the  sensory,  about  the  middle  of 
each  lateral  half.  The  sensory  fibres,  however,  can  be  traced  down  in 
the  medulla  as  far  as  the  upper  part  of  the  cord,  these  latter  fibres  bring- 
ing sensory  impressions  from  the  tongue.  In  addition  to  these  sensory 
fibres,  coming  from  the  nucleus  and  the  spinal  cord,  there  are  it  is  said 
others  coming  from  the  cerebellum.  The  motor  centre  is  connected  with 
the  cerebral  cortex  of  the  opposite  side.  Fibres  for  the  motor  root  also 
come  from  the  corpora  quadrigemina  along  the  aqueduct  of  Sylvius.  The 
first  and  second  divisions  of  the  nerve,  which  arise  wholly  from  the  lar- 
ger root,  are  purely  sensory.  The  third  division  being  joined,  as  before 
said,  by  the  motor  root  of  the  nerve,  is  of  course  both  motor  and  sen- 
sory. 

(a.)  Motor  Functions. — Through  branches  of  the  lesser  or  non- 
ganglionic  portion  of  the  fifth,  the  muscles  of  mastication,  namely,  the 
temporal,  masseter,  two  pterygoid,  anterior  part  of  the  digastric,  and 
mylo-hyoid,  derive  their  motor  nerves.  Filaments  are  also  supplied  to 
the  tensor  tympani  and  tensor  palati.  The  motor  function  of  these 
branches  is  proved  by  the  violent  contraction  of  all  the  muscles  of  masti- 
cation in  experimental  irritation  of  the  third,  or  inferior  maxillary  divi- 
sion of  the  nerve;  by  paralysis  of  the  same  muscles,  when  it  is  divided 
or  disorganized,  or  from  any  reason  deprived  of  power;  and  by  the  re- 
tention of  the  power  of  these  muscles,  when  all  those  supplied  by  the 


534  HANDBOOK    OF    PHYSIOLOGY. 

facial  nerve  lose  their  power  through  paralysis  of  that  nerve.  The  last 
instance  proves  best,  that  though  the  buccinator  muscle  gives  passage  to, 
and  receives  some  filaments  from,  a  buccal  branch  of  the  inferior  divi- 
sion of  the  fifth  nerve,  yet  it  derives  its  motor  power  from  the  facial,  for 
it  is  paralyzed  together  with  the  other  muscles  that  are  supplied  by  the 
facial,  but  retains  its  power  when  the  other  muscles  of  mastication  are 
paralyzed.  Whether,  however,  the  branch  of  the  fifth  nerve  which  is 
supplied  to  the  buccinator  muscle  is  entirely  sensory,  or  in  part  motor 
also,  must  remain  for  the  present  doubtful.  Prom  the  fact  that  this 
muscle,  besides  its  other  functions,  acts  in  concert  or  harmony  with  the 
muscles  of  mastication,  in  keeping  the  food  between  the  teeth,  it  might 
be  supposed  from  analogy,  that  it  would  have  a  motor  branch  from  the 
same  nerve  that  supplies  them.  There  can  be  no  doubt,  however,  that 
the  so-called  buccal  branch  of  the  fifth  is,  in  the  main,  sensory;  although 
it  is  not  quite  certain  that  it  does  not  give  a  few  motor  filaments  to  the 
buccinator  muscle. 

(b.)  Sensory  Functions. — Through  the  branches  of  the  greater  or 
ganglionic  portion  of  the  fifth  nerve,  all  the  anterior  and  antero-lateral 
parts  of  the  face  and  head,  with  the  exception  of  the  skin  of  the  parotid 
region  (which  derives  branches  from  the  cervical  spinal  nerves),  acquire 
common  sensibility;  and  among  these  parts  may  be  included  the  organs 
of  the  special  sense,  from  which  common  sensations  are  conveyed 
through  the  fifth  nerve",  and  their  special  sensations  through  their  sev- 
eral nerves  of  special  sense.  The  muscles,  also,  of  the  face  and  lower 
jaw  acquire  muscular  sensibility,  through  the  filaments  of  the  ganglionic 
portion  of  the  fifth  nerve  distributed  to  them  with  their  proper  motor 
nerves.  The  sensory  function  of  the  branches  of  the  greater  division  of 
the  fifth  nerve  is  proved,  by  all  the  usual  evidences-,  such  as  their  dis- 
tribution in  parts  that  are  sensitive  and  not  capable  of  muscular  con- 
traction, the  exceeding  sensibility  of  some  of  these  parts,  their  loss  of 
sensation  when  the  nerve  is  paralyzed  or  divided,  the  pain  without  con- 
vulsions produced  by  morbid  or  experimental  irritation  of  the  trunk  or 
branches  of  the  nerve,  and  the  analogy  of  this  portion  of  the  fifth  to  the 
posterior  root  of  the  spinal  nerve. 

Other  Functions. — In  relation  to  muscular  movements,  the  branches 
of  the  greater  or  ganglionic  portion  of  the  fifth  nerve  exercise  a  manifold 
influence  on  the  movements  of  the  muscles  of  the  head  and  face,  and 
other  parts  in  which  they  are  distributed.  They  do  so,  in  the  first  place 
(a),  by  providing  the  muscles  themselves  with  that  sensibility  without 
which  the  mind,  being  unconscious  of  their  position  and  state,  cannot 
voluntarily  exercise  them.  It  is,  probably,  for  conferring  this  sensi- 
bility on  the  muscles,  that  the  branches  of  the  fifth  nerve  communicate 
so  frequently  with  those  of  the  facial  and  hypoglossal,  and  the  nerves  of 
the  muscles  of  the  eye;  and  it  is  because  of  the  loss  of  this  sensibility 


PHYSIOLOGY   OF    THE    I'KAXJ.W.    NERVES. 


535 


that  when  the  fifth  nerve  is  divided,  animals  are  always  slow  and  awk- 
ward in  the  movement  of  the  muscles  of  the  face  and  head,  or  hold  them 
still,  or  guide  their  movements  by  the  sight  of  the  objects  towards 
which  they  wish  to  move. 

Again,  the  fifth  nerve  has  an  indirect  influence  on  the  muscular 
movements,  by  (b)  conveying  sensations  of  the  state  and  position  of  the 
skin  and  other  parts:  which  the  mind  perceiving,  is  enabled  to  deter- 
mine appropriate  acts.  Thus,  when  the  fifth  nerve  or  its  infra-orbital 
branch  is  divided,  the  movements  of  the  lips  in  feeding  may  cease,  or  be 
imperfect.     Bell  supposed  that  the  motion  of  the  upper  lip  in  grasping 


Fig.  367.— General  plan  of  the  branches  of  the  fifth  pair.  H.— 1,  lesser  root  of  the  fifth  pair-  2 
greater  root  passing  forwards  into  the  Gasserian  ganglion;  3,  placed  on  the  bone  above  the  ophthal- 
mic nerve,  which  is  seen  dividing  into  the  supra-orbital,  lachrymal,  and  nasal  branches  the  latter 
connected  with  the  ophthalmic  ganglion;  4,  placed  on  the  bone  close  to  the  foramen  rotundum 
marks  the  superior  maxillary  division,  which  is  ci  mneeted  below  with  the  sphenopalatine  ganglion' 
ami  passes  forwards  to  the  infra  orbital  foramen;  5.  placed  on  the  bone  over  the  foramen  ovale' 
marks  the  interior  maxillary  nerve,  giving  off  the  anterior  auricular  and  muscular  branches,  and 
coutinued  by  the  inferior  dental  to  the  lower  jaw,  and  by  the  gustatory  to  the  tongue;  o,  the  sub- 
maxillary eland,  the  submaxillary  ganglion  placed  above  it  in  connection  with  the  gustatory  nerve" 
6,  the  chorda  tympani;  7,  the  facial  nerve  issuing  from  the  stylomastoid  foramen.    (Charles  Bell.) 

food  depended  directly  on  the  infra-orbital  nerve;  for  he  found  that, 
after  he  had  divided  that  nerve  on  both  sides  in  an  ass,  it  no  longer 
seized  the  food  with  its  lips,  but  merely  pressed  them  against  the  ground, 
and  used  the  tongue  for  the  prehension  of  the  food.  Mayo  corrected 
this  error.  He  found,  indeed,  that  after  the  infra-orbital  nerve  had 
been  divided,  the  animal  did  not  seize  its  food  with  the  lip.,  and  could 
not  use  it  well  during  mastication,  but  thai  it  could  open  the  lips.     lie. 


536  HANDBOOK    OF   PHYSIOLOGY. 

therefore,  justly  attributed  the  phenomena  in  Bell's  experiments  to  the 
loss  of  sensation  in  the  lips;  the  animal  not  being  able  to  feel  the  food, 
and,  therefore,  although  it  had  the  power  to  seize  it,  not  knowing  how 
and  where  to  use  that  power. 

The  fifth  nerve  has  also  (c),  an  intimate  connection  with  muscular 
movements  through  the  many  reflex  acts  of  muscles  of  which  it  is  the 
necessary  excitant.  Hence,  when  it  is  divided  and  can  no  longer  convey 
impressions  to  the  nervous  centres  to  be  thence  reflected,  the  irritation 
of  the  conjunctiva  produces  no  closure  of  the  eye,  the  mechanical  irrita- 
tion of  the  nose  excites  no  sneezing. 

Through  its  ciliary  branches  and  the  branch  which  forms  the  long 
root  of  the  ciliary  or  ophthalmic  ganglion,  it  exercises  also  (d),  some 
influence  on  the  movements  of  the  iris. 

When  the  trunk  of  the  ophthalmic  portion  is  divided,  the  pupil  be- 
comes, according  to  Valentin,  contracted  in  men  and  rabbits,  and  dilated 
in  cats  and  dogs;  but  in  all  cases,  becomes  immovable  even  under  all  the 
varieties  of  the  stimulus  of  light.  How  the  fifth  nerve  thus  affects  the 
iris  is  unexplained;  the  same  effects  are  produced  by  destruction  of  the 
superior  cervical  ganglion  of  the  sympathetic,  so  that,  possibly,  they  are 
due  to  the  injury  of  those  filaments  of  the  sympathetic  which,  after 
joining  the  trunk  of  the  fifth,  at  and  beyond  the  Gasserian  ganglion, 
proceed  with  the  branches  of  its  ophthalmic  divisidn  to  the  iris;  or,  as 
has  been  ingeniously  suggested,  the  influence  of  the  fifth  nerve  on  the 
movements  of  the  iris  may  be  ascribed  to  the  affection  of  vision  in  con- 
sequence of  the  disturbed  circulation  or  nutrition  in  the  retina,  when  the 
normal  influence  of  the  fifth  nerve  and  ciliary  ganglion  is  disturbed.  In 
such  disturbance,  increased  circulation  making  the  retina  more  irritable 
might  induce  extreme  contraction  of  the  iris;  or  under  moderate  stimu- 
lus of  light,  producing  partial  blindness,  might  induce  dilatation:  but 
it  does  not  appear  why,  if  this  be  the  true  explanation,  the  iris  should  in 
either  case  be  immovable  and  unaffected  by  the  various  degrees  of  light. 

Trophic  influence. — Furthermore,  the  morbid  effects  which  division 
of  the  fifth  nerve  produces  in  the  organs  of  special  sense,  make  it  prob- 
able that,  in  the  normal  state,  the  fifth  nerve  exercises  some  special  or 
trophic  influence  on  the  nutrition  of  all  these  organs;  although,  in  part, 
the  effect  of  the  section  of  the  nerve  is  only  indirectly  destructive  by 
abolishing  sensation,  and  therefore  the  natural  safeguard  which  leads  to 
the  protection  of  parts  from  external  injury.  Thus,  after  such  division, 
within  a  period  varying  from  twenty-four  hours  to  a  week,  the  cornea 
begins  to  be  opaque;  then  it  grows  completely  white;  a  low  destructive 
inflammatory  process  ensues  in  the  conjunctiva,  sclerotica,  and  interior 
parts  of  the  eye;  and  within  one  or  a  few  weeks,  the  whole  eye  may  be 
quite  disorganized,  and  the  cornea  may  slough  or  be  penetrated  by  a 
large  ulcer.     The  sense  of  smell  (and  not  merely  that  of  mechanical  ir- 


PHYSIOLOGY    OF    THK    CRANIAL    NEBVE8.  .".., 

ritation  of  the  nose),  may  be  at  the  same  time  lost  or  gravely  impaired; 
50  may  the  hearing,  and  commonly,  whenever  the  fifth  nerve  is  para- 
lyzed, the  tongue  loses  the  sense  of  taste  in  its  anterior  and  lateral  parts, 
and  according  to  Gowers  in  the  posterior  part  as  well. 

In  relation  to  Taste. — The  loss  of  tactile  sensibility  as  well  as  the 
sense  of  taste,  is  no  doubt  due  (a)  to  the  lingual  branch  of  the  fifth 
nerve  being  a  nerve  of  tactile  sense,  and  also  because  with  it  runs  the 
chorda  tympani,  which  is  one  of  the  nerves  of  taste;  partly,  also,  it  is 
due  (b),  to  the  fact  that  this  branch  supplies,  in  the  anterior  and  lateral 
parts  of  the  tongue,  a  necessary  condition  for  the  proper  nutrition  of 
that  part;  while  (c),  it  forms  also  one  chief  link  in  the  nervous  circle  for 
reflex  action,  in  the  secretion  of  saliva.  But,  deferring  this  question  un- 
til the  glosso-pharyngeal  nerve  is  to  be  considered,  it  may  be  observed 
that  in  some  brief  time  after  complete  paralysis  or  division  of  the  fifth 
nerve,  the  power  of  all  the  organs  of  the  special  senses  may  be  lost;  they 
may  lose  not  merely  their  sensibility  to  common  impressions,  for  which 
they  all  depend  directly  on  the  fifth  nerve,  but  also  their  sensibility  to 
their  several  peculiar  impressions  for  the  reception  and  conduction  of 
which  they  are  purposely  constructed  and  supplied  with  special  nerves 
besides  the  fifth.  The  facts  observed  in  these  cases  can,  perhaps,  be 
only  explained  by  the  influence  which  the  fifth  nerve  exercises  on  the 
nutritive  processes  in  the  organs  of  the  special  senses.  It  is  not  unrea- 
sonable to  believe,  that,  in  paralysis  of  the  fifth  nerve,  their  tissues  may 
be  the  seats  of  such  changes  as  are  seen  in  the  laxity,  the  vascular  con- 
gestion, oedema,  and  other  affections  of  the  skin  of  tlie  face  and  other 
tegumentary  parts  which  also  accompany  the  paralysis;  and  that  these 
changes,  which  may  appear  unimportant  when  they  affect  external  parts. 
are  sufficient  to  destroy  that  refinement  of  structure  by  which  the  or- 
gans of  the  special  senses  are  adapted  to  their  functions. 

The  Sixth  Nerve,  or  Abducens. 

Functions. — The  Sixth  nerve,  Xervus  abducens  or  ocularis  externus, 
is  also,  like  the  fourth,  exclusively  motor,  and  supplies  only  the  rectus 
externus  muscle.  It  arises  from  the  floor  of  the  fourth  ventricle  from 
the  anterior  region  in  the  deeper  part.  It  is  conuected  (Fig.  367)  with 
the  nuclei  of  the  third,  fourth,  and  seventh  nerves.  It  is  nearer  the 
middle  line  than  the  nuclei  of  the  fifth. 

The  rectus  externus  is  convulsed,  and  the  eye  is  turned  outward-, 
when  the  sixth  nerve  is  irritated;  and  the  muscle  is  paralyzed  when  the 
nerve  is  divided.  In  all  such  cases  of  paralysis,  the  eye  squints  inwards, 
and  cannot  be  moved  outwards. 

In  its  course  through  the  cavernous  sinus,  the  sixth  nerve  form- 
larger  communications  with  the  sympathetic  nerve  than  any  other  nerve 
within  the  cavity  of  the  skull  does.     But  the  import  of  these  communi- 


53S  HANDBOOK    OF    PHYSIOLOGY. 

cations  with  the  sympathetic,   and  the  subsequent   distribution  of  its 
filaments  after  joining  the  sixth  nerve,  are  quite  unknown. 

The  Seventh  or  Facial  Nerve. 

Functions. — The  facial,  or  portio  dura  of  the  seventh  pair  of  nerves, 
arises  from  the  floor  of  the  central  part  of  the  fourth  ventricle  to  the 
outside  of  and  deeper  down  than  the  sixth  nucleus.  It  may  be  con- 
nected with  the  hypoglossal  nucleus.  There  are  two  roots,  the  lower 
and  smaller  is  called  the  portio  intermedia,  is  the  motor  nerve  of  all  the 
muscles  of  the  face,  including  the  platysma,  but  not  including  any  of 
the  muscles  of  mastication  already  enumerated;  it  supplies,  also,  the 
jmrotid  gland,  and  through  the  connection  of  its  trunk  with  the  Vidian 
nerve,  by  the  petrosal  nerves,  some  of  the  muscles  of  the  soft  palate, 
probably  the  levator  palati  and  azygos  uvulae;  by  its  tympanic  branches 
it  supplies  the  stapedius  and  laxator  tympani,  and,  through  the  otic  gan- 
glion, the  tensor  tympani;  through  the  chorda  tympani  it  sends 
branches  to  the  submaxillary  gland  and  to  the  lingualis  and  some  other 
muscular  fibres  of  the  tongue,  and  to  the  mucous  membrane  of  its  an- 
terior two-thirds;  and  by  branches  given  off  before  it  comes  upon  the 
face,  it  supplies  the  muscles  of  the  external  ear,  the  posterior  part  of  the 
digastricus,  and  the  stylo-hyoideus. 

Besides  its  motor  influence,  the  facial  is  also,  by  means  of  the  fibres 
which  are  supplied  to  the  submaxillary  and  parotid  glands,  a  secretory 
nerve.  For,  through  the  last-named  branches,  impressions  may  be  con- 
veyed which  excite  increased  secretion  of  saliva. 

Symptoms  of  Paralysis  of  Facial  Nerve. — When  the  facial  nerve  is 
divided,  or  in  any  other  way  paralyzed,  the  loss  of  power  in  the  muscles 
which  it  supplies,  while  proving  the  nature  and  extent  of  its  functions, 
displays  also  the  necessity  of  its  perfection  for  the  perfect  exercise  of  all 
the  organs  of  the  special  senses.  Thus,  in  paralysis  of  the  facial  nerve, 
the  orbicularis  palpebrarum  being  powerless,  the  eye  remains  open 
through  the  unbalanced  action  of  the  levator  palpebrae;  and  the  conjunc- 
tiva, thus  continually  exposed  to  the  air  and  the  contact  of  dust,  is  liable 
to  repeated  inflammation,  which  may  end  in  thickening  and  opacity  of 
both  its  own  tissue  and  that  of  the  cornea.  These  changes,  however, 
ensue  much  more  slowly  than  those  which  follow  paralysis  of  the  fifth 
nerve,  and  never  bear  the  same  destructive  character. 

The  sense  of  hearing,  also,  is  impaired  in  many  cases  of  paralysis  of 
the  facial  nerve;  not  only  in  such  as  are  instances  of  simultaneous  dis- 
ease in  the  auditory  nerves,  but  in  such  as  may  be  explained  by  the  loss 
of  power  in  the  muscles  of  the  internal  ear.  The  sense  of  smell  is  com- 
monly at  the  same  time  impaired  through  the  inability  to  draw  air 
briskly  towards  the  upper  part  of  the  nasal  cavities  in  which  part  alone 
the  olfactory  nerve  is  distributed;  because,  to  draw  the  air  perfectly  in 


PHYSIOLOGY   OF    THE    CRANIAL    NEK  YES.  ."» :  i  I  # 

this  direction,  the  action  of  the  dilators  and  compressors  of  the  nostrils 
.should  he  perfect. 

Lastly,  the  sense  of  taste  ic  impaired,  or  may  be  wholly  lost  in  para- 
lysis of  the  facial  nerve,  provided  the  source  of  the  paralysis  be  in  some 
part  of  the  nerve  between  its  origin  and  the  giving  off  of  the  chorda  tym- 
pani.  This  result,  which  has  been  observed  in  many  instances  of  disease 
of  the  facial  nerve  in  man,  appears  explicable  on  the  supposition  that  the 
chorda  tympani  is  the  nerve  of  taste  to  the  anterior  two-thirds  of  the 
tongue,  its  fibres  being  distributed  with  the  so-called  gustatory  or  lin- 
gual branch  of  the  fifth.  Some  look  upon  the  chorda  as  partly  or  en- 
tirely made  up  of  fibres  from  the  fifth  nerve,  and  not  strictly  speaking 
as  a  branch  of  the  facial;  others  consider  that  it  receives  its  taste  fibres 
from  communications  with  the  glosso-pharyngeal. 

Together  with  these  effects  of  paralysis  of  the  facial  nerve,  the  mus- 
cles of  the  face  being  all  powerless,  the  countenance  acquires  on  the 
paralyzed  side  a  characteristic,  vacant  look,  from  the  absence  of  all  ex- 
pression: the  angle  of  the  mouth  is  lower,  and  the  paralyzed  half  of  the 
mouth  looks  longer  than  that  on  the  other  side;  the  eye  has  an  unmean- 
ing stare.  All  these  peculiarities  increase,  the  longer  the  paralysis  lasts; 
and  their  appearance  is  exaggerated  when  at  anytime  the  muscles  of  the 
opposite  side  of  the  face  are  made  active  in  any  expression,  or  in  any  of 
their  ordinary  functions.  In  an  attempt  to  blow  or  whistle,  one  side 
of  the  mouth  and  cheek  acts  properly,  but  the  other  side  is  motionless, 
or  flaps  loosely  at  the  impulse  of  the  expired  air;  so  in  trying  to  suck, 
one  side  only  of  the  mouth  acts;  in  feeding,  the  lips  and  cheek  are  pow- 
erless, and  food  lodges  between  the  cheek  and  gum. 

The  Ninth,  or  Glosso-Pharyngeal  Nerve. 

The  glosso-pharyngeal  nerves  (ix.,  Fig.  341),  in  the  enumeration  of 
the  cerebral  nerves  by  numbers  according  to  the  position  in  which  they 
leave  the  cranium,  are  considered  as  divisions  of  the  eighth  pair  of  nerves, 
in  which  term  are  included  with  them  the  pneumogastric  and  accessory 
nerves.  But  the  union  of  the  nerves  under  one  term  is  inconvenient, 
although  in  some  parts  the  glosso-pharyngeal  and  pneumogastric  are 
so  combined  in  their  distribution  that  it  is  impossible  to  separate  them 
in  either  their  anatomy  or  physiology. 

Distribution. — The  glosso-pharyngeal  nerve  gives  filaments  through 
its  tympanic  branch  (Jacobson's  nerve),  to  the  fenestra  ovalis,  and  fe- 
nestra  rotunda,  and  the  Eustachian  tube;  also,  to  the  carotid  plexus,  and, 
through  the  petrosal  nerve,  to  the  spheno-palatine  ganglion.  After 
communicating,  either  within  or  without  the  cranium,  with  the  pneu- 
mogastric, and  soon  after  it  leaves  the  cranium,  with  the  sympathetic, 
digastric  branch  of  the  facial,  and  the  accessory  nerve,  the  glosso-pharyn- 
geal nerve  parts  into  the  two  principal  divisions  indicated  by  its  name, 


540  HANDBOOK    OF    PHYSIOLOGY, 

and  supplies  the  mucous  membrane  of  the  posterior  and  lateral  walls  of 
the  upper  part  of  the  pharynx,  the  Eustachian  tube,  the  arches  of  the 
palate,  the  tonsils  and  their  mucous  membrane,  and  the  tongue  as  far 
forwards  as  the  foramen  caecum  in  the  middle  line,  and  to  near  the  tip 
at  the  sides  and  inferior  part. 

Functions. — The  glosso-pharyngeal  nerve  contains  some  motor  fibres, 
together  with  those  of  common  sensation  and  the  sense  of  taste. 

1.  Its  motor  influences  are  distributed  to  the  glosso-pharyngeal,  the 
stylo-pharyngei,  palato-glossi,  and  constrictors  of  the  pharynx. 

Besides  being  (2)  a  nerve  of  common  sensation  in  the  parts  which 
it  supplies,  and  a  centripetal  nerve  through  which  impressions  are  con- 
Yeyed  to  be  reflected  to  the  adjacent  muscles,  the  glosso-pharyngeal  is 
also  a  nerve  of  special  sensation;  being  the  nerve  of  taste  (from  its 
fibres  derived  from  the  fifth,  Gowers),  in  all  the  parts  of  the  tongue  and 
palate  to  which  it  is  distributed.  After  many  discussions,  the  question, 
"Which  is  the  nerve  of  taste? — the  lingual  branch  of  the  fifth,  or  the 
glosso-pharyngeal? — may  be  most  probably  answered  by  stating  that  they 
are  not  themselves,  strictly  speaking,  nerves  of  this  special  function,  but 
through  their  connection  with  the  fifth  nerve.  For  very  numerous  ex- 
periments and  cases  have  shown  that  when  the  trunk  of  the  fifth  nerve 
is  paralyzed  or  divided,  the  sense  of  taste  is  completely  lost  in  the  supe- 
rior surface  of  the  anterior  and  lateral  parts  of  the  tongue,  at  the  back 
of  the  tongue,  on  the  soft  palate  and  palatine  arches.  The  loss  is  in- 
stantaneous after  division  of  the  nerve;  and,  therefore,  cannot  be 
ascribed  wholly  to  the  defective  nutrition  of  the  part,  though  to  this, 
perhaps,  may  be  ascribed  the  more  complete  and  general  loss  of  the  sense 
of  taste  when  the  whole  of  the  fifth  nerve  has  been  paralyzed. 

The  Tenth  or  Pneumogastric   Nerve.     The  Vagus  or  Par 

Vagum. 

The  origin  of  the  Vagus  nerve  is  in  the  lower  half  of  the  calamus 
scriptorius  in  the  ala  cinerea  (Fig.  365).  Its  nucleus  very  probably 
represents  the  cells  of  Clarke's  posterior  vesicular  column  of  the  spinal 
cord.  In  origin  it  is  closely  connected  with  the  glosso-pharyngeal,  spinal 
accessory,  and  the  hypoglossal. 

It  supplies  sensory  branches,  which  accompany  the  sympathetic  on 
the  middle  meningeal  artery,  and  others  which  supply  the  back  part  of 
the  meatus  and  the  adjoining  part  of  the  external  ear.  It  is  connected 
with  the  petrous  ganglion  of  the  glosso-pharyngeal,  by  means  of  fibres 
to  its  jugular  ganglion;  with  the  spinal  accessory  which  supplies  it  with 
its  motor  fibres  for  the  larger  and  upper  portion  of  the  oesophagus,  and 
with  its  inhibitory  fibres  for  the  heart;  also  with  the  hypoglossal,  with 
the  superior  cervical  ganglion  of  the  sympathetic  and  with  the  cervical 
plexus. 


PHYSIOLOGY    OF    THE    CRANIAL    NERVES. 


41 


Distribution.— The  Pneurhogastric  nerve,  Vermis  Vagus,  or  Par 
Vagum  (1,  Fig.  368),  has,  of  all  the  cranial  and  spinal  nerves,  the  most 
various  distribution,  and  influences  the  most  various  functions,  either 
through  its  own  filaments,  or  through  those  which,  derived  from  other 


Fig.  368.— View  of  thp  nerves  of  the  eighth  pair,  their  distribution  and  connections  nn  the  left 
side.  2  5.— 1,  pneumogastric  nerve  in  the  neck;  •-.>,  ganglion  of  its  trunk-;  8,  its  union  with  the  spinal 
accessory:  4,  its  union  with  the  hypoglossal;  S.pharyngeal  branch;  6,  superior  laryngeal  nerve :  r, 
external  laryngeal;  8,  laryngeal  plexus;  9,  Inferior  or  recurrent  laryngeal;  10,  superior  cardiac 
branch;  11,  middle  cardiac;  IsS,  plextform  part  of  the  nerve  in  the  thorax;  18,  posterior  pnhnonary 
plexus:  14,  Mutual  or  gustatory  nerve  "f  the  inferior  maxillary:  15,  hypoglossal,  passing  into  the 
muscles  of  the  tongue,  giving  its  thyro-hoid  branch,  and  uniting  with  twigs  of  the  ungual;  16, 
glosso-pharyngeal  nerve;  17,  spinal  accessory  nerve,  uniting  by  its  inner  branch  with  the  pneumo- 
gastric. and  by  its  outer,  passing  Into  the  sterno-mast  i.l  muscle;  is.  second  cervical  nerve;  ML 
third;  SO,  fourth;  21,  origin  of  the  phrenic  nerve;  22,  28,  fifth,  sixth,  seventh,  and  eighth  cervical 
nerves,  forming  with  the  first  dorsal  the  brachial  plexus;  24,  superior  cervical  ganfirnon  Ol  the 
sympathetic;  -T..  middle  «-er\  ieal  ganglion:  26,  Inferior  cervical  ganglion  united  with  the  ftrstdorsal 
ganglion;  27,  28,  29,  80,  second,  third,  fourth,  and  fifth  dorsal  ganglia.  cFrom  Sappey  after  llir-i, 
feld  and  Leveillcj 


542  HANDBOOK    OF    PHYSIOLOGY. 

nerves,  are  mingled  in  its  branches.     The  parts  supplied  by  the  branches 
of  the  vagus  nerve  are  as  follows: — 

(1.)  By  its  pharyngeal  branches,  which  enter  the  pharyngeal  plexus, 
a  large  portion  of  the  mucous  membrane,  and,  probably,  all  the  muscles 
of  the  pharynx. 

(2.)  By  the  superior  laryngeal  nerve,  the  mucous  membrane  of  the 
under  surface  of  the  epiglottis,  the  glottis,  and  the  greater  part  of  the 
larynx,  and  the  crico-thyroid  muscle. 

(3.)  By  Van  inferior  laryngeal  nerve,  the  mucous  membrane  and  mus- 
cular fibres  of  the  trachea,  the  lower  part  of  the  pharynx  and  larynx, 
and  all  the  muscles  of  the  larynx  except  the  crico-thyroid. 

(4.)  By  its  oesophageal  branches,  the  mucous  membrane  and  muscular 
coats  of  the  (Esophagus. 

(5.)  Through  the  cardiac  nerves,  moreover,  the  branches  of  the  vagus 
form  a  large  portion  of  the  supply  of  nerves  to  the  heart  and  the  great 
Arteries  derived  from  both  the  trunk  and  the  recurrent  nerve. 

(6.)  Through  both  the  anterior  and  the  posterior  pulmonary  plexuses 
to  the  Lungs. 

(7.)  Through  its  gastric  branches  and  to  the  Stomach,  by  its  termi- 
nal branches  passing  over  the  walls  of  that  organ. 

(8.)  Through  hepatic  and  splenic  branches  the  Liver  and  the  Spleen 
are  partly  supplied  with  nerves. 

Communications. — Throughout  its  whole  course,  the  vagus  contains 
both  sensory  and  motor  fibres;  but  after  it  has  emerged  from  the  skull, 
and,  in  some  instances  even  sooner,  it  enters  into  so  many  anastomoses 
that  it  is  hard  to  say  whether  the  filaments  it  contains  are,  from  their 
origin,  its  own,  or  whether  they  are  derived  from  other  nerves  combining 
with  it.  This  is  particularly  the  case  with  the  filaments  of  the  sym- 
pathetic nerve,  which  are  abundantly  added  to  nearly  all  its  branches. 
The  likeness  to  the  sympathetic  which  it  thus  acquires  is  further  in- 
creased by  its  containing  many  filaments  derived,  not  from  the  brain, 
but  from  its  own  petrosal  ganglia,  in  which  filaments  originate,  in  the 
same  manner  as  in  the  ganglia  of  the  sympathetic,  so  abundantly  that 
the  trunk  of  the  nerve  is  visibly  larger  below  the  ganglia  than  above 
them  (Bidder  and  Volkmann).  Next  to  the  sympathetic  nerve,  that 
which  most  communicates  with  the  vagus  is  the  accessory  nerve,  whose 
internal  branch  joins  its  trunk,  and  is  lost  in  it. 

Functions.— The  particular  functions  which  the  branches  of  the 
pneumogastric  nerve  discharge  in  the  several  parts  to  which  they  are  dis- 
tributed, may  be  thus  summarized.  They  show  that— 1.  The  pharyn- 
geal branch  is  the  principal  motor  nerve  of  the  pharynx  and  soft  palate, 
and  is  most  probably  wholly  motor;  the  chief  part  of  its  motor  fibres 
being  derived  from  the  internal  branch  of  the  accessory  nerve.  2.  The 
inferior  or  recurrent  laryngeal  nerve  is  the  motor  nerve  of  the  larynx. 


PHYSIOLOGY    OF    THE    CRANIAL    NKKVES.  543 

3.  The  superior  laryngeal  nerve  is  chiefly  sensory:  the  muscles  supplied 
by  it  being  the  crico-thyroid,  the  arytenoid  in  part  (?),  and  the  inferior 
constrictor  of  the  pharynx.  4.  The  motions  of  the  (esophagus,  the 
stomach  and  part  of  the  small  intestines  are  dependent  on  motor  fibres 
of  the  vagus,  and  are  probably  excited  by  impressions  made  upon  sensi- 
tive fibres  of  the  same.  5.  The  cardiac  branches  communicate,  from 
tbe  centre  in  the  medullary  channel,  impulses  (inhibitory)  regulating 
the  action  of  the  heart.  G.  The  pulmonary  branches  form  the  principal 
channel  by  which  the  sensory  impressions  on  the  mucous  surface  of  the 
trachea,  bronchi  and  lungs  that  influence  respiration,  are  transmitted  to 
the  medulla  oblongata;  and  some  fibres  also  supply  motor  influence  to 
the  muscular  portions  of  the  fibres  of  the  trachea  and  bronchi.  7. 
Branches  to  the  stomach  and  intestine  not  only  convey  motor  but  also 
vaso-motor  impulses  to  those  organs.  8.  The  action  of  the  so-called  de- 
pressor branch  (p.  149)  in  inhibiting  the  action  of  the  vaso-motor  centre 
has  already  been  treated  of,  and  also  the  influence  of  the  vagus  in  stimu- 
lating the  secretion  of  the  salivary  glands,  as  in  the  nausea  which  pre- 
cedes vomiting. 

To  summarize,  therefore,  the  many  functions  of  this  nerve,  it  may  be 
said. that  it  supplies  (1)  motor  influence  to  the  pharynx  and  oesophagus, 
stomach  and  small  intestine,  the  larynx,  trachea,  bronchi  and  lung;  ('-2) 
sensory  and  in  part  (3)  vaso-motor  influence  in  the  same  regions;  (4) 
inhibitory  influence  to  the  heart ;  (5)  inhibitory  afferent  impulses 
to  the  vaso-motor  centre  ;  (C)  excito-secretory  to  the  salivary 
glands;  (7)  excito-motor  in  coughing,  vomiting,  etc. 

Effects  of  Section. — Division  of  both  vagi,  or  of  both  their  recurrent 
branches,  is  often  very  quickly  fatal  in  young  animals;  but  in  old  ani- 
mals the  division  of  the  recurrent  nerve  is  not  generally  fatal,  and  that 
of  both  vagi  is  not  always  fatal,  and,  when  it  is  so,  death  ensues  slowly. 
This  difference  is,  probably,  because,  the  yielding  of  the  cartilages  of  the 
larynx  in  young  animals  permits  the  glottis  to  be  closed  by  the  atmo- 
spheric pressure  in  inspiration,  and  trfey  are  thus  quickly  suffocated 
unless  tracheotomy  be  performed.  In  old  animals,  the  rigidity  ami 
prominence  of  the  arytenoid  cartilages  prevent  the  glottis  from  being 
completely  closed  by  the  atmospheric  pressure;  even  when  all  the  mus- 
cles are  paralyzed,  a  portion  at  its  posterior  part  remains  open,  ami 
through  this  the  animal  continues  to  breathe. 

In  the  case  of  slower  death,  after  division  of  both  the  vagi,  the  lungs 
are  commonly  found  gorged  with  blood,  oedematous,  or  nearly  solid,  with 
a  kind  of  low  pneumonia,  and  witli  their  bronchial  tubes  full  of  frothy 
bloody  fluid  and  mucus,  changes  to  which,  in  general,  the  death  may  be 
proximately  ascribed.  These  changes  are  due,  perhaps  in  part,  to  the 
influence  which  the  nerves  exercise  on  the  movements  of  tin'  air-cells  and 
bronchi;  yet,  since  they  are  not  always  produced  in  one  lung  when  its 


544  HANDBOOK    OF    PHYSIOLOGY. 

nerve  is  divided,  they  cannot  be  ascribed  wholly  to  the  suspension  of 
organic  nervous  influence.  Rather,  they  may  be  ascribed  to  the  hindrance 
to  the  passage  of  blood  through  the  lungs,  in  consequence  of  the  dimin- 
ished supply  of  air  and  the  excess  of  carbonic  acid  in  the  air-cells  and  in 
the  pulmonary  capillaries;  in  part,  perhaps,  to  paralysis  of  the  blood- 
vessels, leading  to  congestion;  and  in  part,  also,  they  appear  due  to  the 
passage  of  food  and  of  the  various  secretions  of  the  mouth  and  fauces 
through  the  glottis,  which,  being  deprived  of  its  sensibility,  is  no  longer 
stimulated  or  closed  in  consequence  of  their  contact. 

References  to  other  functions  of  Vagi. — Regarding  the  influence 
of  the  vagus,  see  also  Heart  (p.  131),  Arteries  (p.  149  \,  Salivary  Gland 
(p.  237),  Glottis  and  Larynx  (p.  440),  Respiration  (p.  197),  Pharynx  and 
(Esophagus  (p.  245),  Stomach  (p.  256). 

The  Eleventh  or  Spinal  Accessory  Nerve. 

Origin  mid  Connections. — The  nerve  arises  by  two  distinct  origins — 
one  from  a  centre  in  the  floor  of  the  4th  ventricle,  partly  but  chiefly  in 
the  medulla,  and  connected  with  the  vagus  nucleus;  the  other,  from  the 
outer  side  of  the  anterior  corner  of  the  spinal  cord  as  low  down  as  the 
5th  or  6th  cervical  vertebra.  The  fibres  from  the  two  origins  come  to- 
gether at  the  jugular  foramen,  but  separate  again  into  two  branches,  the 
inner  of  which,  arising  from  the  medulla,  joins  the  vagus,  to  which  it 
supplies  its  motor  fibres,  consisting  of  small  medullated  or  visceral  nerve- 
fibres,  whilst  the  outer  consisting  of  large  medullated  fibres,  supplies  the 
trapezius  and  sterno-mastoid  muscles.  The  small-fibred  branch  probably 
arises  from  a  nucleus  which  corresponds  to  the  posterior  vesicular  column 
of  Clarke. 

The  principal  branch  of  the  accessory  nerve,  its  external  branch,  then 
supplies  the  sterno-mastoid  and  trapezius  muscles;  and,  though  pain  is 
produced  by  irritating  it,  is  composed  almost  exclusively  of  motor  fibres. 
The  internal  branch  accessory  nerve  supplies  chiefly  viscero-motor  fila- 
ments to  the  vagus.  The  muscles  of  the  larynx,  all  of  which,  as  already 
stated,  are  supplied,  apparently,  by  branches  of  the  vagus,  are  said  to 
derive  their  motor  nerves  from  the  accessory;  and  (which  is  a  very  sig- 
nificant fact)  Vrolik  states  that  in  the  chimpanzee  the  internal  branch 
of  the  accessory  does  not  join  the  vagus  at  all,  but  goes  direct  to  the 
larynx. 

Among  the  roots  of  the  accessory  nerve,  the  lower  or  external,  arising 
from  the  spinal  cord,  appears  to  be  composed  exclusively  of  motor  fibres, 
and  to  be  destined  entirely  to  the  trapezius  and  sterno-mastoid  muscles; 
the  upper  fibres,  arising  from  the  medulia  oblongata,  contain  many 
sensory  as  well  as  motor  fibres. 


PHYSIOLOGY    OF    THE    CRANIAL    NERVES.  545 

The  Twelfth  or  Hypoglossal  Nerve. 

Origin  and  Connections. — The  hypoglossal  nerve  arises  from  two 
large  celled  and  one  small  celled,  nuclei  in  the  lowest  part  of  the  floor  of 
the  4th  ventricle  near  the  middle  line.  The  fibres  of  origin  are  contin- 
uous with  the  anterior  roots  of  the  spinal  nerves.  It  is  connected  with 
the  vagus,  the  superior  cervical  ganglion  of  the  sympathetic  and  with  the 
upper  cervical  nerves. 

Distribution. — The  hypoglossal  or  ninth  nerve,  or  motor  Ungues,  has 
a  peculiar  relation  to  the  muscles  connected  with  the  hyoid  bone,  includ- 
ing those  of  the  tongue.  It  supplies  through  its  descending  branch 
(descendens  noni),  the  sterno-hyoid,  sterno-thyroid,  and  omo-hyoid; 
through  a  special  branch,  the  thyro-hyoid,  and  through  its  lingual 
branches  the  genio-hyoid,  stylo-glossus,  hyo-glossus,  and  genio-hyo-glos- 
sus  and  linguales.  It  contributes,  also,  to  the  supply  of  the  submaxil- 
lary gland. 

Functions  .—The  function  of  the  hypoglossal  is  exclusively  motor, 
except  in  so  far  as  its  descending  branch  may  receive  a  few  sensory  fila- 
ments from  the  first  cervical  nerve.  As  a  motor  nerve,  its  influence  on 
all  the  muscles  enumerated  above  is  shown  by  their  convulsions  when  it 
is  irritated,  and  by  their  loss  of  power  when  it  is  paralyzed.  The  effects 
of  the  paralysis  of  one  hypoglossal  nerve  are,  however,  not  very  striking 
in  the  tongue.  Often,  in  cases  of  hemiplegia  involving  the  functions  of 
the  hypoglossal  nerve,  it  is  not  possible  to  observe  any  deviation  in  the 
direction  of  the  protruded  tongue;  probably  because  the  tongue  is  so 
compact  and  firm  that  the  muscles  on  either  side,  their  insertion  being 
nearly  parallel  to  the  median  line,  can  push  it  straight  forwards  or  turn 
it  for  some  distance  towards  either  side. 

Spinal  Nerves. 

Functions. — Little  need  be  added  to  what  has  been  already  said  of 
these  nerves  (pp.  480,  481).  The  anterior  roots  of  the  spinal  nerves  are 
formed  exclusively  of  motor  fibres;  the  posterior  roots  exclusively  of 
sensory  fibres.  Beyond  the  ganglia,  all  the  spinal  nerves  are  mixed 
nerves,  and  contain  as  well  sympathetic  filaments. 
35 


CHAPTER   XX. 

THE   SENSES. 

General  Considerations. — Through  the  medium  of  the  Nervous  sys- 
tem the  miud  obtains  a  knowledge  of  the  existence  both  of  the  various 
parts  of  the  body,  and  of  the  external  world.  This  knowledge  is  based 
upon  sensations  resulting  from  the  stimulation  of  certain  centres  in  the 
brain,  by  irritations  conveyed  to  them  by  afferent  (sensory)  nerves. 
Under  normal  circumstances,  the  following  structures  are  necessary  for 
sensation:  {a)  A  peripheral  organ  for  the  reception  of  the  impression; 
(b)  a  nerve  for  conducting  it;  (c)  a  nerve-centre  for  feeling  or  perceiving 
it. 

Classification  of  Sensations. — Sensations  may  be  conveniently  classed 
as  (1)  common  and  (2)  special. 

(1.)  Common  Sensations. — Under  this  head  fall  all  those  general 
sensations  which  cannot  be  distinctly  localized  in  any  particular  part  of 
the  body,  such  as  Fatigue,  Discomfort,  Faintness,  Satiety,  together  with 
Hunger  and  Thirst,  in  which,  in  addition  to  a  general  discomfort,  there 
is  in  many  persons  a  distinct  sensation  referred  to  the  stomach  or  fauces. 
In  this  class  must  also  be  placed  the  various  irritations  of  the  mucous 
membrane  of  the  bronchi,  which  give  rise  to  coughing,  and  also  the  sen- 
sations derived  from  various  viscera  indicating  the  necessity  of  expelling 
their  contents;  e.  g.,  the  desire  to  defaecate,  to  urinate,  and,  in  the 
female,  the  sensations  which  precede  the  expulsion  of  the  foetus.  We 
must  also  include  such  sensations  as  itching,  creeping,  tickling,  tingling, 
burning,  aching,  etc.,  some  of  which  come  under  the  head  of  pain  :  they 
will  be  again  referred  to  in  describing  the  sense  of  Touch.  It  is  impos- 
sible to  draw  a  very  clear  line  of  demarcation  between  many  of  the  com- 
mon sensations  above  mentioned,  and  the  sense  of  touch,  which  forms 
the  connecting  link  between  the  general  and  special  sensations.  Touch 
is,  indeed,  usually  classed  with  the  special  senses,  and  will  be  considered 
in  the  same  group  with  them;  yet  it  differs  from  them  in  being  common 
to  many  nerves;  e.  g.,  all  the  sensory  spinal  nerves,  the  vagus,  glosso- 
pharyngeal, and  fifth  cerebral  nerves,  and  in  its  impressions  being  com- 
municable through  many  organs.  Among  common  sensations  must  also 
be  ranked  the  muscular  sense,  which  has  been  already  alluded  to.  It  is 
by  means  of  this  sense  that  we  become  aware  of  the  condition  of  con- 


THE    SENSES.  5±7 

traction  or  relaxation  of  the  various  muscles  and  groups  of  muscles,  and 
thus  obtain  the  information  necessary  for  their  adjustment  to  various 
purposes — standing,  walking,  grasping,  etc.  This  muscular  sensibility 
is  shown  in  our  power  to  estimate  the  differences  between  weights  by  the 
different  muscular  efforts  necessary  to  raise  them.  Considerable  delicacy 
may  be  attained  by  practice,  and  the  difference  between  194-  oz.  in  one 
hand  and  20  oz.  in  the  other  is  readily  appreciated. 

This  sensibility  with  which  the  muscles  are  endowed  must  be  care- 
fully distinguished  from  the  sense  of  contact  and  of  pressure,  of  which 
the  skin  is  the  organ.  When  standing  erect,  we  can  feel  the  ground 
(contact),  and  further  there  is  a  sense  of  pressure,  due  to  our  feet  being 
pressed  against  the  ground  by  the  weight  of  the  body.  Both  these  are 
derived  from  the  skin  of  the  sole  of  the  foot.  If  now  we  raise  the  body 
on  the  toes,  we  are  conscious  (muscular  sense)  of  a  muscular  effort  made 
by  the  muscles  of  the  calf,  which  overcomes  a  certain  resistance. 

(2.)  Special  Sensations. — Including  the  sense  of  touch,  the  special 
senses  are  five  in  number — Touch,  Taste,  Smell,  Hearing,  Sight. 

Difference  between  Common  and  Special  Sensations. — The  most  im- 
portant distinction  between  common  and  special  sensations  is  that  by 
the  former  we  are  made  aware  of  certain  conditions  of  various  parts  of 
our  bodies,  while  from  the  latter  we  gain  our  knowledge  of  the  external 
world  also.  This  difference  will  be  clear  if  we  compare  the  sensations  of 
pain  and  touch,  the  former  of  which  is  a  common,  the  latter  a  special 
sensation.  "  If  we  place  the  edge  of  a  sharp  knife  on  the  skin,  we  feel 
the  edge  by  means  of  our  sense  of  touch;  we  perceive  a  sensation,  and 
refer  it  to  the  object  which  has  caused  it.  But  as  soon  as  we  cut  the 
skin  with  the  knife,  we  feel  pain,  a  feeling  which  we  no  longer  refer  to 
the  cutting  knife,  but  which  we  feel  within  ourselves,  and  which  com- 
municates to  us  the  fact  of  a  change  of  condition  in  our  own  body.  By 
the  sensation  of  pain  we  are  neither  able  to  recognize  the  object  which 
caused  it,  nor  its  nature." 

General  Characteristics :  Seat. — In  studying  the  phenomena  of  sen- 
sation, it  is  important  clearly  to  understand  that  the  Sensorium,  or  seat 
of  sensation,  is  in  the  Brain,  and  not  in  the  particular  organ  (eye,  ear, 
etc.)  through  which  the  sensory  impression  is  received.  In  common 
parlance  we  are  said  to  see  with  the  eye,  hear  with  the  ear,  etc. ,  but  in 
reality  these  organs  are  only  adapted  to  receive  impressions  which  are 
conducted  to  the  sensorium,  through  the  optic  and  auditory  nerves  re- 
spectively, and  there  give  rise  to  sensation. 

Hence,  if  the  optic  nerve  is  severed  (although  the  eye  itself  is  per- 
fectly uninjured),  vision  is  no  longer  possible;  since,  although  the  image 
falls  on  the  retina  as  before,  the  sensory  impression  can  no  longer  be 
conveyed  to  the  sensorium.  "Wheu  any  given  sensation  is  felt,  all  that 
we  can  with  certaintv  affirm  is  that  the  sensorium  in  the  brain  is  excited. 


548  HANDBOOK    OF  PHYSIOLOGY. 

The  exciting  cause  may  be  (in  the  vast  majority  of  cases  is),  some  ob- 
ject of  the  external  world  (objective  sensation);  or  the  condition  of  the 
sensorium  may  be  due  to  some  excitement  within  the  brain,  in  which 
case  the  sensation  is  termed  subjective.  The  mind  habitually  refers 
sensations  to  external  causes;  and  hence,  whenever  they  are  subjective 
(due  to  causes  within  the  brain),  we  can  hardly  divest  ourselves  of  the 
idea  of  an  external  cause,  and  an  illusion  is  the  result. 

Illusions. — Numberless  examples  of  such  illusions  might  be  quoted. 
As  familiar  cases  may  be  mentioned,  humming  and  buzzing  in  the  ears 
caused  by  some  irritation  of  the  auditory  nerve  or  centre,  and  even  musi- 
cal sounds  and  voices  (sometimes  termed  auditory  spectra);  also  so-called 
optical  illusions:  persons  and  other  objects  are  described  as  being  seen, 
although  not  present.  Such  illusions  are  most  strikingly  exemplified  in 
cases  of  delirium  tremens  or  other  forms  of  delirium,  in  which  cats, 
rats,  creeping  loathsome  forms,  etc.,  are  described  by  the  patient  as 
seen  with  great  vividness. 

Cases  of  Illusions. — One  uniform  internal  cause,  which  may  act  on 
all  the  nerves  of  the  senses  in  the  same  manner,  is  the  accumulation  of 
blood  in  their  capillary  vessels,  as  in  congestion  and  inflammation. 
This  one  cause  excites  in  the  retina,  while  the  eyes  are  closed,  the  sen- 
sation's of  light  and  luminous  flashes;  in  the  auditory  nerve,  the  sensa- 
tion of  humming  and  ringing  sounds;  in  the  olfactoi-y  nerve,  the  sense 
of  odors;  and  in  the  nerves  of  feeling,  the  sensation  of  pain.  In  the 
same  way,  also,  a  narcotic  substance  introduced  into  the  blood,  excites 
in  the  nerves  of  each  sense  peculiar  symptoms:  in  the  optic  nerves  the 
appearance  of  luminous  sparks  before  the  eyes;  in  the  auditory  nerves 
"  tinnitus  aurium;  "  and  in  the  common  sensory  nerves,  the  sensation  of 
creeping  over  the  surface.  So,  also,  among  external  causes,  the  stimu- 
lus of  electricity,  or  the  mechanical  influence  of  a  blow,  concussion,  or 
pressure,  excites  in  the  eye  the  sensation  of  light  and  colors;  in  the  ear, 
a  sense  of  a  loud  sound  or  of  ringing;  in  the  tongue,  a  saline  or  acid 
taste;  and  in  the  other  parts  of  the  body,  a  perception  of  peculiar  jar- 
ring or  of  the  mechanical  impression,  or  a  shock  like  it. 

Experiments  seem  to  have  proved,  however,  that  none  of  the  nerves 
of  special  sense  possess  the  faculty  of  common  sensibility.  Thus,  Ma- 
gendie  observed  that  when  the  olfactory  nerves,  laid  bare  in  a  dog,  were 
pricked,  no  signs  of  pain  were  manifested;  and  other  experiments  of  his 
seem  to  show  that  both  the  retina  and  optic  nerve  are  insusceptible  of 
pain.  Further,  the  optic  nerve  is  insusceptible  to  the  stimulus  of  light 
when  severed  from  its  connection  with  the  retina  which  alone  is  adapted 
to  receive  luminous  impressions. 

Sensations  and  Perceptions. — The  habit  of  constantly  referring 
our  sensations  to  external  causes,  leads  us  to  interpret  the  various  modi- 
fications which  external  objects  produce  in  our  sensations,  -as,  properties 

I 


THE    SENSES.  549 

of  the  external  bodies  themselves.  Thus  we  speak  of  certain  substances 
as  possessing  a  disagreeable  taste  and  smell;  whereas,  the  fact  is,  their 
taste  and  smell  are  only  disagreeable  to  us.  It  is  evident,  however,  that 
on  this  habit  of  referring  our  sensations  to  causes  outside  ourselves  (per- 
ception), depends  the  reality  of  the  external  world  to  us;  and  more 
especially  is  this  the  case  with  the  senses  of  touch  and  sight.  By  the  co- 
operation of  these  two  senses,  aided  by  the  others,  we  are  enabled  gradu- 
ally to  attain  a  knowledge  of  external  objects  which  daily  experience 
confirms,  until  we  come  to  place  unbounded  confidence  in  what  is 
termed  the  "  evidence  of  the  senses." 

Judgments. — We  must  draw  a  distinction  between  mere  sensations, 
and  the  judgments  based,  often  unconsciously,  upon  them.  Thus,  in 
looking  at  the  near  object,  we  unconsciously  estimate  its  distance,  and 
say  it  seems  to  be  ten  or  twelve  feet -off:  but  the  estimate  of  its  distance 
is  in  reality  &  judgment  based  on  many  things  besides  the  appearance  of 
the  object  itself;  among  which  may  be  mentioned  the  number  of  the  in- 
tervening objects,  the  number  of  steps  which  from  past  experience  we 
know  we  must  take  before  we  could  touch  it,  and  many  others. 

Sensation  of  Motion  is,  like  motion  itself,  of  two  kinds — progressive 
and  vibratory.  The  faculty  of  the  perception  of  progressive  motion  is 
possessed  chiefly  by  the  senses  of  vision,  touch,  and  taste.  Thus  an  im- 
pression is  perceived  travelling  from  one  part  of  the  retina  to  another, 
and  the  movement  of  the  image  is  interpreted  by  the  mind  as  the  motion 
of  the  object.  The  same  is  the  case  in  the  sense  of  touch;  so  also  the 
movement  of  a  sensation  of  taste  over  the  surface  of  the  organ  of  taste, 
can  be  recognized.  The  motion  of  tremors,  or  vibrations,  is  perceived 
by  several  senses,  but  especially  by  those  of  hearing  and  touch. 

Sensations  of  Chemical  Actions. — "We  are  made  acquainted  with 
chemical  actions  principally  by  taste,  smell,  and  touch,  and  by  each  of 
these  senses  in  the  mode  proper  to  it.  Volatile  bodies,  disturbing  the 
conditions  of  the  nerves  by  a  chemical  action,  exert  the  greatest  influ- 
ence upon  the  organ  of  smell;  and  many  matters  act  on  that  sense  which 
produce  no  impression  upon  the  organs  of  taste  and  touch — for  example, 
many  odorous  substances,  as  the  vapor  of  metals,  such  as  lead,  and  the 
vapor  of  many  minerals.  Some  volatile  substances,  however,  are  per- 
ceived not  only  by  the  sense  of  smell,  but  also  by  the  senses  of  touch  and 
taste.  Thus,  the  vapors  of  horse-radish  and  mustard,  and  acrid  suffo- 
cating gases,  act  upon  the  conjunctiva  and  the  mucous  membrane  of  the 
lungs,  exciting  through  the  common  sensory  nerves,  merely  modifica- 
tions of  common  feeling;  and  at  the  same  time  they  excite  the  sensa- 
tions of  smell  and  of  taste. 


550  handbook  of  physiology. 

The  Special  Senses. 

I.  Touch. 

Seat. — The  sense  of  touch  is  not  confined  to  particular  parts  of  the 
body  of  small  extent,  like  the  other  senses;  on  the  contrary,  all  parts 
capable  of  perceiving  the  presence  of  a  stimulus  by  ordinary  sensation 
are,  in  certain  degrees,  the  seat  of  this  sense;  for  touch  is  simply  a  modi- 
fication or  exaltation  of  common  sensation  or  sensibility.  The  nerves 
on  which  the  sense  of  touch  depends  are,  therefore,  the  same  as  those 
which  confer  ordinary  sensation  on  the  different  parts  of  the  body,  viz., 
those  derived  from  the  posterior  roots  of  the  nerves  of  the  spinal  cord, 
and  the  sensory  cerebral  nerves. 

But,  although  all  parts  of  the  body  supplied  with  sensory  nerves  are 
thus,  in  some  degree,  organs  of  touch,  yet  the  sense  is  exercised  in  per- 
fection only  in  those  parts  the  sensibility  of  which  is  extremely  delicate, 
e.  g.,  the  skin,  the  tongue,  and  the  lips,  which  are  provided  with  abun- 
dant papillae.  A  peculiar  and,  of  its  own  kind  in  each  case,  a  very 
acute  sense  of  touch  is  exercised  through  the  medium  of  the  nails  and 
teeth.  To  a  less  extent  the  hair  may  be  reckoned  an  organ  of  touch;  as 
in  the  case  of  the  eyelashes.  The  sense  of  touch  renders  us  conscious  of 
the  presence  of  a  stimulus,  from  the  slightest  to  the  most  intense  degree 
of  its  action,  by  that  indescribable  something  which  we  call  feeling,  or 
common  sensation.  The  modifications  of  this  sense  often  depend  on  the 
extent  of  the  parts  affected.  The  sensation  of  pricking,  for  example, 
informs  us  that  the  sensitive  particles  are  intensely  affected  in  a  small 
extent;  the  sensation  of  pressure  indicates  a  slighter  affection  of  the 
parts  in  the  greater  extent,  and  to  a  greater  depth.  It  is  by  the  depth 
to  which  the  parts  are  affected  that  the  feeling  of  pressure  is  distinguished 
from  that  of  mere  contact. 

Varieties. — (a)  The  sense  of  Touch,  strictly  so-called  (tactile  sensi- 
bility), (b)  the  sense  of  Pressure,  (c)  the  sense  of  Temperature. 
These  when  carried  beyond  a  certain  degree  are  merged  in  (d)  the  sen- 
sation of  Pain. 

Various  peculiar  sensations,  such  as  tickling,  must  be  classed  with 
pain  under  the  head  of  common  sensations,  since  they  give  us  no  infor- 
mation as  to  external  objects.  Such  sensations,  whether  pleasurable  or 
painful,  are  in  all  cases  referred  by  the  mind  to  the  part  affected,  and 
not  to  the  cause  which  stimulates  the  sensory  nerves  of  the  part.  The 
sensation  of  tickling  may  be  produced  in  many  parts  of  the  body,  but 
with  especial  intensity  in  the  soles  of  the  feet.  Among  other  sensations 
belonging  to  this  class,  and  confined  to  particular  parts  of  the  body,  may 
be  mentioned  those  of  the  genital  organs  and  nipples. 

(a)  Touch  proper. — In  almost  all  parts  of  the  body  which  have 
delicate  tactile  sensibility  the  epidermis,  immediately  over  the  papillae, 


THE    SENSES.  551 

is  moderately  thin.  When  its  thickness  is  much  increased,  as  over  the 
heel,  the  sense  of  touch  is  very  much  dulled.  On  the  other  hand,  when 
it  is  altogether  removed,  and  the  cutis  laid  bare,  the  sensation  of  contact 
is  replaced  by  one  of  pain.  Further,  in  all  highly  sensitive  parts,  the 
papillae  are  numerous  and  highly  vascular,  and  usually  the  sensory 
nerves  are  connected  with  special  End-organs. 

The  acuteness  of  the  sense  of  touch  depends  very  largely  on  the 
cutaneous  circulation,  which  is  of  course  largely  influenced  by  external 
temperature.  Hence  the  numbness,  familiar  to  every  one,  produced  by 
the  application  of  cold  to  the  skin. 

Special  organs  of  touch  are  present  in  most  animals,  among  which 
may  be  mentioned  the  antennae  of  insects,  the  "  whiskers  "  (vibrissas)  of 
cats  and  other  carnivora,  the  wings  of  bats,  the  trunk  of  the  elephant, 
and  the  hand  of  man. 

Judgment  of  the  Form  and  Size  of  Bodies. — By  the  sense  of  touch  the 
mind  is  made  acquainted  with  the  size,  form,  and  other  external  charac- 
ters of  bodies.  And  in  order  that  these  characters  may  be  easily  ascer- 
tained, the  sense  of  touch  is  especially  developed  in  those  parts  which 
can  be  readily  moved  over  the  surface  of  bodies.  Touch,  in  its  more 
limited  sense,  or  the  act  of  examining  a  body  by  the  touch,  consists 
merely  in  a  voluntary  employment  of  this  sense  combined  with  movement, 
and  stands  in  the  same  relation  to  the  sense  of  touch,  or  common  sensi- 
bility, generally,  as  the  act  of  seeking,  following,  or  examining  odors, 
does  to  the  sense  of  smell.  The  hand  is  best  adapted  for  it,  by  reason 
of  its  peculiarities  of  structure, — namely,  its  capability  of  pronation  and 
supination,  which  enables  it,  by  the  movement  of  rotation,  to  examine 
the  whole  circumference  of  the  body;  the  power  it  possesses  of  opposing 
the  thumb  to  the  rest  of  the  hand,  and  the  relative  mobility  of  the  fin- 
gers; and  lastly  from  the  abundance  of  the  sensory  terminal  organs 
which  it  possesses.  In  forming  a  conception  of  the  figure  and  extent  of 
a  surface,  the  mind  multiplies  the  size  of  the  hand  or  fingers  used  in  the 
inquiry  by  the  number  of  times  which  it  is  contained  in  the  surface  tra- 
versed; and  by  repeating  this  process  with  regard  to  the  different  dimen- 
sions of  a  solid  body,  acquires  a  notion  of  its  cubical  extent,  but,  of 
course,  only  an  imperfect  notion,  as  other  senses,  e.  g.,  the  sight,  are 
required  to  make  it  complete. 

Acuteness  of  Touch. — The  perfection  of  the  sense  of  touch  on  differ- 
ent parts  of  the  surface  is  proportioned  to  the  power  which  such  parts 
possess  of  distinguishing  and  isolating  the  sensations  produced  by  two 
points  placed  close  together.  This  power  depends,  at  least  in  part,  on 
the  number  of  primitive  nerve-fibres  distributed  to  the  part;  for  the 
fewer  the  primitive  fibres  which  an  organ  receives,  the  more  likely  is  it 
that  several  impressions  on  different  contiguous  points  will  act  on  only 


552 


HANDBOOK    OF   PHYSIOLOGY. 


one  nervous  fibre,  and  hence  be  confounded,  and  perhaps  produce  but 
one  sensation.  Experiments  have  been  made  to  determine  the  tactile 
properties  of  different  parts  of  the  skin,  as  measured  by  this  power  of 
distinguishing  distances.  These  consist  of  touching  the  skin,  while  the 
eyes  are  closed,  with  the  points  of  a  pair  of  compasses  sheathed  with 
cork,  and  in  ascertaining  how  close  the  points  of  compasses  might  be 
brought  to  each  other,  and  still  be  felt  as  two  bodies. 

Table  of  variations  in  the  tactile  sensibility  of  different  parts. 

— Tlie  measurement  indicates  the  least  distance  at  which  the  tivo 
blunted  points  of  a  pair  of  compasses  could  be  separately  distin- 
guished.    (E.  H.  Weber. )' 


Tip  of  tongue,    . 

Palmar  surface  of  third  phalanx  of  forefinger, 

Palmar  surface  of  second  phalanges  of  fingers, 

Ked  surface  of  under-lip, 

Tip  of  the  nose.  .... 

Middle  of  dorsum  of  tongue, 

Palm  of  hand,     .... 

Centre  of  hard  palate, 

Dorsal  surface  of  first  phalanges  of  fingers, 

Back  of  hand, 

Dorsum  of  foot  near  toes, 

Gluteal  region, 

Sacral  region,       .... 

Upper  and  lower  parts  of  forearm,    . 

Back  of  neck  near  occiput, 

Upper  dorsal  and  mid-lumbar  regions, 

Middle  part  of  forearm, 

Middle  of  thigh, 

Mid-cervical  region, 

Mid-dorsal  region, 


rV  inch. 


■?4 
1 

1 
6 


7 

A 

il 
H 
i* 

2 
2 

a* 

n 


Moreover,  in  the  case  of  the  limbs,  it  was  found  that  before  they 
were  recognized  as  two,  the  points  of  the  compasses  had  to  he  further 
separated  when  the  line  joining  them  was  in  the  long  axis  of  the  limb, 
than  when  in  the  transverse  direction. 

According  to  Weber  the  mind  estimates  the  distance  between  two 
points  by  the  number  of  unexcited  nerve-endings  which  intervene  be- 
tween the  two  points  touched.  It  would  appear  that  a  certain  number 
of  intervening  unexcited  nerve-endings  are  necessary  before  two  points 
touched  can  be  recognized  as  separate,  and  the  greater  this  number  the 
more  clearly  are  the  points  of  contact  distinguished  as  separate.  By 
practice  the  delicacy  of  a  sense  of  touch  may  be  very  much  increased. 
A  familiar  illustration  occurs  in  the  case  of  the  blind,  who,  by  constant 
practice,  can  acquire  the  power  of  reading  raised  letters  the  forms  of 
which  are  almost  if  not  quite  undistinguishable,  by  the  sense  of  touch  to 
an  ordinary  person. 


THE    SENSES.  553 

The  power  of  correctly  localizing  sensations  of  touch  is  gradually 
derived  from  experience.  Thus  infants  when  in  pain  simply  cry,  but 
make  no  effort  to  remove  the  cause  of  irritation,  as  an  older  child  or 
adult  would,  doubtless  on  account  of  their  imperfect  knowledge  of  its 
exact  situation.  By  long  experience  this  power  of  localization  becomes 
perfected,  till  at  length  the  brain  possesses  a  complete  "picture"  as  it 
were  of  the  surface  of  the  body,  and  is  able  with  marvellous  exactness  to 
localize  each  sensation  of  touch. 

Illusions  of  Touch. — The  different  degrees  of  sensitiveness  possessed 
by  different  parts  may  give  rise  to  errors  of  judgment  in  estimating  the 
distance  between  two  points  where  the  skin  is  touched.  Thus,  if  blunted 
points  of  a  pair  of  compasses  (maintained  at  a  constant  distance  apart) 
be  slowly  drawn  over  the  skin  of  the  cheek  towards  the  lips,  it  is  almost 
impossible  to  resist  the  conclusion  that  the  distance  between  the  points 
is  gradually  increasing.  When  they  reach  the  lips  they  seem  to  be  con- 
siderably further  apart  than  on  the  cheek.  Thus,  too,  our  estimate  of 
the  size  of  a  cavity  in  a  tooth  is  usually  exaggerated  when  based  upon 
sensation  derived  from  the  tongue  alone.  Another  curious  illusion  may 
here  be  mentioned.  If  we  close  the  eyes,  and  place  a  small  marble  or 
pea  between  the  crossed  fore  and  middle  fingers,  we  seem  to  be  touching 
two  marbles.  This  illusion  is  due  to  an  error  of  judgment.  The  marble 
is  touched  by  two  surfaces  which,  under  ordinary  circumstances,  could 
only  be  touched  by  two  separate  marbles,  hence,  the  mind  taking  no 
cognizance  of  the  fact  that  the  fingers  are  crossed,  forms  the  conclusion 
that  two  sensations  are  due  to  two  marbles. 

(b)  Pressure. — It  is  extremely  difficult  to  separate  touch  proper 
from  sensations  of  pressure,  and,  indeed,  the  former  may  be  said  to  de- 
pend upon  the  latter.  If  the  hand  be  rested  on  the  table  and  a  very 
light  body  such  as  a  small  card  placed  on  it,  the  only  sensation  produced 
is  one  of  contact;  if,  however,  an  ounce  weight  be  laid  on  the  card  an 
additional  sensation  (that  of  pressure)  is  experienced,  and  this  becomes 
more  intense  as  the  weight  is  increased.  If  now  the  weight  be  raised 
by  the  hand,  we  are  conscious  of  overcoming  a  certain  resistance;  this 
consciousness  is  due  to  what  is  termed  the  "muscular  sense."  The  esti- 
mate of  a  weight  is,  therefore,  usually  based  on  two  sensations,  (1)  of 
pressure  on  the  skin,  and  (2)  the  muscular  sense. 

The  estimate  of  weight  derived  from  a  combination  of  these  two  sen- 
sations (as  in  lifting  a  weight)  is  more  accurate  than  that  derived  from 
the  former  alone  (as  when  a  weight  is  laid  on  the  hand);  thus  Weber 
found  that  by  the  former  method  he  could  generally  distinguish  19£  oz. 
from  20  oz.,  but  not  19$  oz.  from  20,  while  by  the  latter  he  could  at 
most  only  distinguish  144  oz.  from  15  oz. 

It  is  not  the  absolute,  but  the  relative,  amount  of  the  difference  of 
weight  which  we  have  thus  the  faculty  of  perceiving. 


554  HANDBOOK    OF   PHYSIOLOGY. 

It  is  not.  however,  certain  that  our  idea  of  the  amount  of  muscular 
force  used  is  derived  solely  from  sensation  in  the  muscles.  We  have  the 
power  of  estimating  very  accurately  beforehand,  and  of  regulating,  the 
amount  of  nervous  influence  necessary  for  the  production  of  a  certain 
degree  of  movement.  When  we  raise  a  vessel,  with  the  contents  of 
which  we  are  not  acquainted,  the  force  we  employ  is  determined  by  the 
idea  we  have  conceived  of  its  weight.  If  it  should  happen  to  contain 
some  very  heavy  substance,  as  quicksilver,  we  shall  probably  let  it  fall; 
the  amount  or  muscular  action,  or  of  nervous  energy,  which  we  had  ex- 
erted being  insufficient.  The  same  thing  occurs  sometimes  to  a  person 
descending  stairs  in  the  dark;  he  makes  the  movement  for  the  descent 
of  a  step  which  does  not  exist.  It  is  possible  that  in  the  same  way  the 
idea  of  weight  and  pressure  in  raising  bodies,  or  in  resisting  forces,  may 
in  part  arise  from  a  consciousness  of  the  amount  of  nervous  energy 
transmitted  from  the  brain  rather  than  from  a  sensation  in  the  muscles 
themselves.  The  mental  conviction  of  the  inability  longer  to  support  a 
weight  must  also  be  distinguished  from  the  actual  sensation  of  fatigue 
in  the  muscles. 

So,  with  regard  to  the  ideas  derived  from  sensations  of  touch  combined 
with  movements,  it  is  doubtful  how  far  the  consciousness  of  the  extent 
of  muscular  movement  is  obtained  from  sensations  in  the  muscles  them- 
selves. The  sensation  of  movement  attending  the  motions  of  the  hand 
is  very  slight;  and  persons  who  do  not  know  that  the  action  of  particu- 
lar muscles  is  necessary  for  the  production  of  given  movements,  do  not 
suspect  that  the  movement  of  the  fingers,  for  example,  depends  on  an 
action  in  the  forearm.  The  mind  has,  nevertheless,  a  very  definite 
knowledge  of  the  changes  of  position  produced  by  movements;  and  it  is 
on  this  that  the  ideas  which  it  conceives  of  the  extension  and  form  of  a 
body  are  in  great  measure  founded. 

(c)  Temperature. — The  whole  surface  of  the  body  is  more  or  less 
sensitive  to  differences  of  temperature.  The  sensation  of  heat  is  distinct 
from  that  of  touch;  and  it  would  seem  reasonable  to  suppose  that  there 
are  special  nerves  and  nerve-endings  for  temperature.  At  any  rate,  the 
power  of  discriminating  temperature  may  remain  unimpaired  when  the 
sense  of  touch  is  temporarily  in  abeyance.  Thus  if  the  ulnar  nerve  be 
compressed  at  the  elbow  till  the  sense  of  touch  is  very  much  dulled  in 
the  fingers  which  it  supplies,  the  sense  of  temperature  remains  quite  un- 
affected. 

The  sensations  of  heat  and  cold  are  often  exceedingly  fallacious,  and 
in  many  cases  are  no  guide  at  all  to  the  absolute  temperature  as  indicated 
by  a  thermometer.  All  that  we  can  with  safety  infer  from  our  sensations 
of  temperature,  is  that  a  given  object  is  warmer  or  cooler  than  the  skin. 
Thus  the  temperature  of  our  skin  is  the  standard;  and  as  this  varies  from 
hour  to  hour  according  to  the  activity  of  the  cutaneous  circulation,  our 
estimate  of  the  absolute  temperature  of  any  body  must  necessarily  vary 
too.  If  we  put  the  left  hand  into  water  at  40°  F.  and  the  right  into 
water  at  110°  F.,  and  then  immerse  both  in  water  at  80°  F.,  it  will  feel 
warm  to  the  left  hand  but  cool  to  the  right.     Again,  a  piece  of  metal 


THE    SENSES.  .  555 

which  has  really  the  same  temperature  as  a  given  piece  of  wood  will  feel 
much  colder,  since  it  conducts  away  the  heat  much  more  rapidly.  For 
the  same  reason  air  in  motion  feels  very  much  cooler  than  air  of  the  same 
temperature  at  rest. 

Perhaps  the  most  striking  example  of  the  fallaciousness  of  our  sensa- 
tions as  a  measure  of  temperature  is  afforded  by  fever.  In  a  shivering 
fit  of  ague  the  patient  feels  excessively  cold,  whereas  his  actual  tempera- 
ture is  several  degrees  above  the  normal,  while  in  the  sweating  stage 
which  succeeds  it  he  feels  very  warm,  whereas  really  his  temperature  has 
fallen  several  degrees.  In  the  former  case  the  cutaneous  circulation  is 
much  diminished,  in  the  latter  much  increased;  hence  the  sensations  of 
cold  and  heat  respectively. 

In  some  cases  we  are  able  to  form  a  fairly  accurate  estimate  of  abso- 
lute temperature.  Thus,  by  plunging  the  elbow  into  a  bath,  a  practised 
bath-attendant  can  tell  the  temperature  sometimes  within  1°  F. 

The  temperatures  which  can  be  readily  discriminated  are  between 
50°-115°  F.  (10°-15°  C);  very  low  and  very  high  temperatures  alike 
produce  a  burning  sensation.  A  temperature  appears  higher  according 
to  the  extent  of  cutaneous  surface  exposed  to  it.  Thus,  water  of  a  tem- 
perature which  can  be  readily  borne  by  the  hand,  is  quite  intolerable  if 
the  whole  body  be  immersed.  So,  too,  water  appears  much  hotter  to 
the  hand  than  to  a  single  finger. 

The  delicacy  of  the  sense  of  temperature  coincides  in  the  main  with 
that  of  touch,  and  appears  to  depend  largely  on  the  thickness  of  the 
skin;  hence,  in  the  elbow,  where  the  skin  is  thin,  the  sense  of  tempera- 
ture is  delicate,  though  that  of  touch  is  not  remarkably  so.  Weber  has 
further  ascertained  the  following  facts:  two  compass  points  so  near  to- 
gether on  the  skin  that  they  produce  but  a  single  impression,  at  once 
give  rise  to  two  sensations,  when  one  is  hotter  than  the  other.  More- 
over, of  two  bodies  of  equal  weight,  that  which  is  the  colder  feels  heavier 
than  the  other. 

As  every  sensation  is  attended  with  an  idea,  and  leaves  behind  it  an 
idea  in  the  mind  which  can  be  reproduced  at  will,  we  are  enabled  to  com- 
pare the  idea  of  a  past  sensation  with  another  sensation  really  present. 
Thus  we  can  compare  the  weight  of  one  body  with  another  which  we  had 
previously  felt,  of  which  the  idea  is  retained  in  our  mind.  "Weber  was 
indeed  able  to  distinguish  in  this  manner  between  temperatures,  experi- 
enced one  after  the  other,  better  than  between  temperatures  to  which  the 
two  hands  were  simultaneously  subjected.  This  power  of  comparing 
present  with  past  sensations  diminishes,  however,  in  proportion  to  the 
time  which  has  elapsed  between  them.  After-sensations  left  by  impres- 
sions on  nerves  of  common  sensibility  or  touch  are  very  vivid  and  dura- 
ble. As  long  as  the  condition  into  which  the  stimulus  has  thrown  the 
organ  endures,  the  sensation  also  remains,  though  the  exciting  cause 


556  HANDBOOK    OF    PHYSIOLOGY. 

should  have  long  ceased  to  act.     Both  painful  and  pleasurable  sensations 
afford  many  examples  of  this  fact. 

Subjective  sensations,  or  sensations  dependent  on  internal  causes,  are 
in  no  sense  more  frequent  than  in  the  sense  of  touch.  All  the  sensations 
of  pleasure  and  pain,  of  heat  and  cold,  of  lightness  and  weight,  of 
fatigue,  etc.,  may  be  produced  by  internal  causes.  Neuralgic  pain,  the 
sensation  of  rigor,  formication  or  the  creeping  of  ants,  and  the  states  of 
the  sexual  organs  occurring  during  sleep,  afford  striking  examples  of 
subjective  sensations.  The  mind  has  a  remarkable  power  of  exciting 
sensations  in  the  nerves  of  common  sensibility;  just  as  the  thought  of 
the  nauseous  excites  sometimes  the  sensation  of  nausea,  so  the  idea  of 
pain  gives  rise  to  the  actual  sensation  of  pain  in  a  part  predisposed  to  it; 
numerous  examples  of  this  influence  might  be  quoted. 

II.— Taste. 

Conditions  necessary. — The  conditions  for  the  perceptions  of  taste 
are* — 1,  the  presence  of  a  nerve  and  nerve-centre  with  special  endow- 
ments; 2,  the  excitation  of  the  nerve  by  the  sapid  matters,  which  for 
this  purpose  must  be  in  a  state  of  solution.  The  nerves  concerned  in 
the  production  of  the  sense  of  taste  have  been  already  considered  (pp. 
537  and  540).  The  mode  of  action  of  the  substances  which  excite  taste 
consists  in  the  production  of  a  change  in  the  condition  of  the  gustatory 
nerves,  and  the  conduction  of  the  stimulus  thus  produced  to  the  nerve- 
centre;  and,  according  to  the  difference  of  the  substances,  an  infinite  va- 
riety of  changes  of  condition  of  the  nerves,  and  consequently  of  stimula- 
tions of  the  gustatory  centre,  may  be  induced.  The  matters  to  be  tasted 
must  either  be  in  solution  or  be  soluble  in  the  moisture  covering  the 
tongue;  hence  insoluble  substances  are  usually  tasteless,  and  produce 
merely  sensations  of  touch.  Moreover,  for  the  perfect  action  of  a  sapid, 
as  of  an  odorous  substance,  it  is  necessary  that  the  sentient  surface 
should  be  moist.  Hence,  when  the  tongue  and  fauces  are  dry,  sapid 
substances,  even  in  solution,  are  with  difficulty  tasted. 

The  nerves  of  taste,  like  the  nerves  of  other  special  senses,  may  have 
their  peculiar  properties  excited  by  various  other  kinds  of  irritation,  such 
as  electricity  and  mechanical  impressions.  Thus,  a  small  current  of  air 
directed  upon  the  tongue  gives  rise  to  a  cool  saline  taste,  like  that  of 
saltpetre;  and  a  distinct  sensation  of  taste  similar  to  that  caused  by 
electricity,  may  be  produced  by  a  smart  tap  applied  to  the  papillae  of  the 
tongue.  Moreover,  the  mechanical  irritation  of  the  fauces  and  palate 
produces  the  sensation  of  nausea,  which  is  probably  only  a  modification 
of  taste. 

Seat. — The  principal  seat  (apparent  seat,  that  is,  to  our  senses)  of 
the  sense  of  taste  is  the  tongue.  But  the  results  of  experiments  as  well 
as  ordinary  experience  show   that  the  soft  palate  and  its  arches,  the 


THE    SENSES.  b&l 

uvula,  tonsils,  and  probably  the  upper  part  of  the  pharynx,  are  also  en- 
dowed with  taste.  These  parts,  together  with  the  base  and  posterior 
parts  of  the  tongue,  are  supplied  with  branches  of  the  glossopharyngeal 
nerve,  and  evidence  has  been  already  adduced  that  the  sense  of  taste  is 
conferred  upon  them  by  this  nerve.  In  most,  though  not  in  all  persons, 
the  anterior  parts  of  the  tongue,  especially  the  edges  and  tip,  are  en- 
dowed with  the  sense  of  taste.  The  middle  of  the  dorsum  is  only  feebly 
endowed  with  this  sense,  probably  because  of  the  density  and  thickness 
of  the  epithelium  covering  the  filiform  papilla?  of  this  part  of  the  tongue, 
which  will  prevent  the  sapid  substances  from  penetrating  to  their  sensi- 
tive parts. 

The  Tongue. 

Structure. — The  tongue  is  a  muscular  organ  covered  by  mucous  mem- 
brane. The  muscles,  which  form  the  greater  part  of  the  substance  of 
the  tongue  {intrinsic  muscles)  are  termed  linguales;  and  by  these, 
which  are  attached  to  the  mucous  membrane  chiefly,  its  smaller  and 
more  delicate  movements  are  chiefly  performed. 

By  other  muscles  {extrinsic  muscles),  as  the  genio-hyoglossus,  the 
styloglossus,  etc.,  the  tongue  is  fixed  to  surrounding  parts;  and  by  this 
group  of  muscles  its  larger  movements  are  performed. 

The  mucous  membrane  of  the  tongue  resembles  other  mucous  mem- 
branes in  essential  points  of  structure,  but  contains  papilla,  more  or  less 
peculiar  to  itself;  peculiar,  however,  in  details  of  structure  and  arrange- 
ment, not  in  their  nature.  The  tongue  is  beset  with  numerous  mucous 
follicles  and  glands.  The  use  of  the  tongue  in  relation  to  mastication 
and  deglutition  has  already  been  considered. 

The  larger  papillce  of  the  tongue  are  thickly  set  over  the  anterior 
two-thirds  of  its  upper  surface,  or  dorsum  (Fig.  369),  and  give  to  it 
its  characteristic  roughness.  In  carnivorous  animals,  especially  those  of 
the  cat  tribe,  the  papillae  attain  a  large  size,  and  are  developed  into  sharp 
recurved  horny  spines.  Such  papillae  cannot  be  regarded  as  sensitive, 
but  they  enable  the  tongue  to  play  the  part  of  a  most  efficient  rasp,  as 
in  scraping  bones,  or  of  a  comb  in  cleaning  fur.  Their  greater  promi- 
nence than  those  of  the  skin  is  due  to  their  interspaces  not  being  filled 
up  with  epithelium,  as  the  interspaces  of  the  papilla?  of  the  skin  are. 
The  papilla?  of  the  tongue  present  several  diversities  of  form;  but  three 
principal  varieties,  differing  both  in  seat  and  general  characters,  may 
usually  be  distinguished,  namely,  the  (1)  drcumvallate,  the  (%)  fungi- 
form, and  the  (3)  filiform  papilla.  Essentially  these  have  ;ill  of  them 
the  same  structure,  that  is  to  say,  they  are  all  formed  by  a  projection  of 
the  mucous  membrane,  and  contain  special  branches  of  blood-vessels  and 
nerves.  In  details  of  structure,  however,  they  differ  considerably  one 
from  another. 


558 


HANDBOOK    OF    PHYSIOLOGY, 


The  surface  of  each  kind  is  studded  by  minute  conical  processes  of 
mucous  membrane,  which  thus  form  secondary  papilla?. 

Simple  papillae  also  occur  over  most  other  parts  of  the  tongue 
not  occupied  by  the  compound  papilla?,  and  extend  for  some  distance 
behind  the  papilla?  circumvallata?.  They  are  commonly  buried  beneath 
the  epithelium;  hence  they  are  often  overlooked.  The  mucous  mem- 
brane immediately  in  front  of  the  epiglottis  is,  however,  free  from  them. 


Fia.  369.—  Papillar  surface  of  the  tongue,  with  the  fauces  and  tonsils.  1,  1,  circumvallate 
papillae,  in  front  of  2,  the  foramen  caecum:  3,  fungiform  papillae;  4,  filiform  and  conical  papillae; 
5,  transverse  and  oblique  rugae;  6,  mucous  glands  at  the  base  of  the  tongue  and  in  the  fauces;  7, 
tonsils;  8,  part  of  the  epiglottis;  9,  median  glosso-epiglottidean  fold  (fraenum  epiglottidis).  (From 
Sappey.) 

(1.)  Circumvallate. — These  papilla?  (Fig.  370),  eight  or  ten  in  num- 
ber, are  situate  in  two  V-shaped  lines  at  the  base  of  the  tongue  (1,  1, 
Fig.  3G9).  They  are  circular  elevations  from  ^ih  to  TVth  of  an  inch 
wide,  each  with  a  central  depression,  and  surrounded  by  a  circular  fissure, 
at  the  outside  of  which  again  is  a  slightly  elevated  ring,  both  the  central 


THK    SENSES. 


559 


elevation  and  the  ring  being  formed  of  close-set  simple  papilla?  (Fig. 
370). 

(2.)  Fungiform. — The  fungiform  papilla?  (3,  Fig.  369)  are  scattered 
chiefly  over  the  sides  and  tip,  and  sparingly  over  the  middle  of  the  dor- 
sum, of  the  tongue;  their  name  is  derived  from  their  being  usually  nar- 
rower at  their  base  than  at  their  summit.     They  also  consist  of  groups 


Fig.  370.— Vertical  section  of  a  circumvallate  papilla  of  the  calf.  1  and  3,  epithelial  layers  cov- 
ering it;  2.  taste  goblets;  4  and 4',  duct  of  serous  gland  opening  out  into  the  pit  in  which  papilla  is 
situated;  5  and  6,  nerves  ramifying  within  the  papilla.     ( Engelniann.  > 

of  simple  papilla?  (A.  Fig.  371),  each  of  which  contains  in  its  interior  a 
loop  of  capillary  blood-vessels  (B.),  and  a  nerve  fibre. 

(3.)  Conical  or  Filiform. — These,  which  are  the  most  abundant 
papilla?,  are  scattered  over  the  whole  surface  of  the  tongue,  but  espe- 
cially over  the  middle  of  the  dorsum.     They  vary  in  shape  somewhat, 


M A  i 


a*-- 


Fig.  371.— Surface  and  section  of  the  fungiform  papilla?.  A,  the  surface  of  a  fungiform  papilla, 
partially  denuded  of  its  epithelium;  p,  secondary  papilla?;  e,  epithelium.  B,  section  of  a  fungiform 
papilla  with  the  blood-vessels  injected;  a,  artery;  v,  vein;  c,  capillary  loops  of  similar  papilla?  iu 
neighboring  structure  of  the  tongue;  d,  capillary  loops  of  the  secondary  papilla?;  e,  epithelium. 
^From  Kiilliker,  after  Todd  and  Bowman.) 


but  for  the  most  part  are  conical  or  filiform,  and  covered  by  a  thick 
laj'er  of  epidermis,  which  is  arranged  over  them,  either  in  an  imbricated 
manner,  or  is  prolonged  from  their  surface  in  the  form  of  fine  stiff  pro- 
jections, hair-like  in  appearance,  and  iu  some  instances  in  structure  also 
(Fig.  371).  From  their  peculiar  structure,  it  seems  likely  that  these 
papilla?  have  a  mechanical  function,  or  one  allied  to  that  of  touch  rather 


560 


HANDBOOK    OF    PHYSIOLOGY. 


than  of  taste;  the  latter  sense   being  probably  seated  esjaecially  in  the 
other  two  varieties  of  papillae,  the  circumvallate  and  the  fungiform. 

The  epithelnim  of  the  tongue  is  stratified  with  the  upper  layers  of 
the  squamous  kind.  It  covers  every  part  of  the  surface;  but  over  the 
fungiform  papillae  forms  a  thinner  layer  than  elsewhere.  The  epithe- 
lium covering  the  filiform  papillae  is  extremely  dense  and  thick,  and  as 
before  mentioned,  projects  from  their  sides  and  summits  in  the  form  of 
long,  stiff,  hair-like  processes  (Fig.  372).  Many  of  these  processes  bear 
a  close  resemblance  to  hairs.  Blood-vessels  and  nerves  are  supplied 
freely  to  the  papillae.     The  nerves  in  the  fungiform  and  circumvallate 


Fig.  372.— Two  filiform  papillae,  one  with  epithelium,  the  other  without  35/1.— d,  the  substance- 
of  the  papillae  dividing  at  their  upper  extremities  into  secondary  papillae ;  o,  artery,  and  v,  vein,  di- 
viding into  capillary  loops;  e,  epithelial  covering,  laminated  between  the  papillae,  but  extended  into 
hair-like  processes, /,  from  the  extremities  of  the  secondary  papillae.  (From  Kolliker,  after  Todd 
and  Bowman,  j 

papillae  form  a  kind  of  plexus,  spreading  out  brush-wise  (Fig.  370),  but 
the  exact  mode  of  termination  of  the  nerve-filaments  is  not  certainly 
knowu. 

Taste  Goblets. — In  the  circumvallate  papillae  of  the  tongue  of  man 
peculiar  structures  known  as  gustatory  buds  or  taste  goblets,  have  been 
discovered.  They  are  of  an  oval  shape,  and  consist  of  a  number  of 
closely  packed,  very  narrow  and  fusiform,  cells  {gustatory  cells).  This 
central  core  of  gustatory  cells  is  inclosed  in  a  single  layer  of  broader  fu- 


THE    SENSES. 


561 


siform  cells  {encasing  cells).  The  gustatory  cells  terminate  in  fine  spikes 
not  unlike  cilia,  which  project  on  the  free  surface  (Fig.  a,  373). 

These  bodies  also  occur  side  by  side  in  considerable  numbers  in  the 
epithelium  of  the  papilla  foliata,  which  is  situated  near  the  root  of  the 
tongue  in  the  rabbit,  and  also  in  man.  Similar  taste-goblets  have  been 
observed  on  the  posterior  (laryngeal)  surface  of  the  epiglottis.  It  seems 
probable,  from  their  distribution,  that  these  taste-goblets  are  gustatory 
in  function,  though  no  nerves  have  been  distinctly  traced  into  them. 

Other  Functions. — Besides  the  sense  of  taste,  the  tongue,  by  means 
also  of  its  papillas,  is  endued  (2)  especially  at  its  side  and  tip,  with  a 
very  delicate  and  accurate  sense  of  touch  which  renders  it  sensible  of  the 
impressions  of  heat  and  cold,  pain  and  mechanical  pressure,  and  conse- 
quently of  the  form  of  surfaces.  The  tongue  may  lose  its  common  sen- 
sibility, and  still  retain  the  sense  of  taste,  and  vice  verscl.  This  fact 
renders  it  probable  that,  although  the  senses  of  taste  and  of  touch  may 


Fig.  373.—  Taste-goblet  from  dog's  epiglottis  ( laryngeal  surface  near  the  base) .  precisely  similar 
in  structure  to  those  found  in  the  tongue,  a,  depression  in  epithelium  over  goblet;  below  the,  letter 
are  seen  the  fine  hair-like  processes  in  which  the  cells  terminate;  c,  two  nuclei  of  the  axial  (gusta- 
tory) cells.  The  more  superficial  nuclei  belong  to  the  superficial  (encasing)  cells;  the  converging 
lines  indicate  the  fusiform  shape  of  the  encasing  cells.     X  400.    (Schofield.) 


be  exercised  by  the  same  papilla?  supplied  by  the  same  nerves,  yet  the 
nervous  conductors  for  these  two  different  sensations  are  distinct,  just 
as  the  nerves  for  smell  and  common  sensibility  in  the  nostrils  are  distinct; 
and  it  is  quite  conceivable  that  the  same  nervous  trunk  may  contain 
fibres  differing  essentially  in  their  specific  properties.  Facts  already 
detailed  seem  to  prove  that  the  lingual  branch  of  the  fifth  nerve  is  the 
conductor  of  sensations  of  taste  in  the  anterior  part  of  the  tongue;  and 
it  is  also  certain,  from  the  marked  manifestations  of  pain  to  which  its 
division  in  animals  gives  rise,  that  it  is  likewise  a  nerve  of  common  sen- 
sibility. The  glosso-pharyngeal  also  seems  to  contain  fibres  both  of 
common  sensation  and  of  the  special  sense  of  taste. 

The  functions  of  the  tongue  in  connection  with  (3)  speech,  (4)  mas- 
tication,   (5)   deglutition,  (6)   suction,  have   been   referred  to  in   other 

chanters. 

3(5 


,562  HANDBOOK    OF    PHYSIOLOGY. 

Taste  and  Smell:  Perceptions. — The  concurrence  of  common  and 
special  sensibility  in  the  same  part  makes  it  sometimes  difficult  to  deter- 
mine whether  the  impression  produced  by  a  substance  is  perceived 
through  the  ordinary  sensitive  fibres,  or  through  those  of  the  sense  of 
taste.  In  many  cases,  indeed,  it  is  probable  that  both  sets  of  nerve-fibres 
are  concerned,  as  when  irritating  acrid  substances  are  introduced  into 
the  mouth. 

Much  of  the  perfection  of  the  sense  of  taste  is  often  due  to  the  sapid 
substances  being  also  odorous,  and  exciting  the  simultaneous  action  of 
the  sense  of  smell.  This  is  shown  by  the  imperfection  of  the  taste  of 
such  substances  when  their  action  on  the  olfactory  nerves  is  prevented 
by  closing  the  nostrils.  Many  fine  wines  lose  much  of  their  apparent 
excellence  if  the  nostrils  are  held  close  while  they  are  drunk. 

Varieties  of  Tastes. — Among  the  most  clearly  defined  tastes  are  the 
sweet  and  bitter  (which  are  more  or  less  opposed  to  each  other),  the  acid, 
alkaline,  and  saline  tastes.  Acid  and  alkaline  taste  may  be  excited  by 
electricity.  If  a  piece  of  zinc  be  placed  beneath  and  a  piece  of  copper 
above  the  tongue,  and  their  ends  brought  into  contact,  an  acid  taste 
(due  to  the  feeble  galvanic  current)  is  produced.  The  delicacy  of  the 
sense  of  taste  is  sufficient  to  discern  1  part  of  sulphuric  acid  in  1000  of 
water;  but  it  is  far  surpassed  in  acuteness  by  the  sense  of  smell. 

After-taste. — Very  distinct  sensations  of  taste  are  frequently  left 
after  the  substances  which  excited  them  have  ceased  to  act  on  the  nerve; 
and  such  sensations  often  endure  for  a  long  time,  and  modify  the  taste 
of  other  substances  applied  to  the  tongue  afterwards.  Thus,  the  taste 
of  sweet  substances  spoils  the  flavor  of  wine,  the  taste  of  cheese  improves 
it.  There  appears,  therefore,  to  exist  the  same  relation  between  tastes 
as  between  colors,  of  which  those  that  are  opposed  or  complementary 
render  each  other  more  vivid,  though  no  general  principles  governing 
this  relation  have  been  discovered  in  the  case  of  tastes.  In  the  art 
of  cooking,  however,  attention  has  at  all  times  been  paid  to  the  conso- 
nance or  harmony  of  flavors  in  their  combination  or  order  of  succession, 
just  as  in  painting  and  music  the  fundamental  principles  of  harmony 
have  been  employed  empirically  while  the  theoretical  laws  were  unknown. 

Frequent  and  continued  repetitions  of  the  same  taste  render  the  per- 
ception of  it  less  and  less  distinct,  in  the  same  way  that  a  color  becomes 
more  and  more  dull  and  indistinct  the  longer  the  eye  is  fixed  upon  it. 
Thus,  after  frequently  tasting  first  one  and  then  the  other  of  two  kinds 
of  wine,  it  becomes  impossible  to  discriminate  between  them. 

The  simple  contact  of  a  sapid  substance  with  the  surface  of  the  gus- 
tatory organ  seldom  gives  rise  to  a  distinct  sensation  of  taste;  it  needs 
to  be  diffused  over  the  surface,  and  brought  into  intimate  contact  with 
the  sensitive  parts  by  compression,  friction,  and  motion  between  the 
tongue  and  palate. 


THE    SENSES.  g£3 

Subjective  Sensations  of  Taste. — The  sense  of  taste  seems  capable  of 
being  excited  only  by  external  causes,  such  as  changes  in  the  conditions 
of  the  nerves  or  nerve-centres,  produced  by  congestion  or  other  causes, 
which  excite  subjective  sensations  in  the  other  organs  of  sense.  But 
little  is  known  of  the  subjective  sensations  of  taste;  for  it  is  difficult  to 
distinguish  the  phenomena  from  the  effects  of  external  causes,  such  as 
changes  in  the  nature  of  the  secretions  of  the  mouth. 

III.— Smell. 

Conditions  necessary. — •(!.)  The  first  conditions  essential  to  the  sense 
of  smell  are  a  special  nerve  and  nerve-centre,  the  changes  in  whose  con- 
dition are  perceived  in  sensations  of  odor,  for  no  other  nervous  structure 
is  capable  of  these  sensations,  even  though  acted  on  by  the  same  causes. 
The  same  substance  which  excites  the  sensation  of  smell  in  the  olfactory 
centre. may  cause  another  peculiar  sensation  through  the  nerves  of  taste, 
and  may  produce  an  irritating  and  burning  sensation  on  the  nerves  of 
touch;  but  the  sensation  of  odor  is  yet  separate  and  distinct  from  these, 
though  it  may  be  simultaneously  perceived.     (2.)  The  second  condition 
of  smell  is  a  peculiar  change  produced  in  the  olfactory  nerve  and  its 
centre  by  the  stimulus  or  odorous  substance.     (3.)  The  material  causes 
of  odors  are,  usually,  in  the  case  of  animals  living  in  the  air,  either  solids 
suspended  in  a  state  of  extremely  fine  division  in  the  atmosphere;  or 
gaseous  exhalations  often  of  so  subtile  a  nature  that  they  can  be  detected 
by  no  other  reagent  than  the  sense  of  smell  itself.     The  matters  of  odor 
must,  in  all  cases,  be  dissolved  in  the  mucus  of  the  mucous  membrane 
before  they  can  be  immediately  applied  to,  or  affect  the  olfactory  nerves; 
therefore  a  further  condition  necessary  for  the  perception  of  odors  is, 
that  the  mucous  membrane  of  the  nasal  cavity  be  moist.     When  the 
Schneideriau  membrane  is  dry,  the  sense  of  smell  is  impaired  or  lost;  in 
the  first  stage  of  catarrh,  when  the  secretion  of  mucus  within  the  nostrils 
is  lessened,  the  faculty  of  perceiving  odor  is  either  lost,  or  rendered  very 
imperfect.     (4.)  In  animals  living  in  the  air,  it  is  also  requisite  that  the 
odorous  matter  should  be  transmitted  in  a  current  through  the  nostrils. 
This  is  effected  by  an  inspiratory  movement,  the  mouth  being  closed; 
hence  we  have  voluntary  influence  over  the  sense  of  smell;  for  by  inter- 
rupting respiration  we  prevent  the  perception  of  odors,  and  by  repeated 
quick  inspiration,  assisted,  as  in  the  act  of  sniffing,  by  the  action  of  the 
nostrils,  we  render  the  impression  more  intense.     An  odorous  substance 
in  a  liquid  form  injected  into  the  nostrils  appears  incapable  of  giving  rise 
to  the  sensation  of  smell;  thus  Weber  could  not  smell  the  slightest  odor 
when  his  nostrils  were  completely  filled  with  water  containing  a  large 
quantity  of  eau-de-Cologne. 

Seat. — The  human  organ  of  smell  is  formed  by  the  filaments  of  the 
olfactory   nerves,  distributed   in   the   mucous   membrane   covering  the 


564 


HANDBOOK    OF    PHYSIOLOGY. 


upper  third  of  the  septum  of  the  nose,  the  superior  turbinated  or  spongy 
bone,  the  upper  part  of  the  middle  turbinated  bone,  and  the  upper  wall 


vgpic  ywm 


&im***&* 


Fig.  374.— Nerves  of  the  septum  nasi,  seen  from  the  right  side.  2i. — I,  the  olfactory  hulb;  1,  the 
olfactory  nerves  passing  through  the  foramina  of  the  cribriform  plate,  and  descending  to  be  distrib- 
uted on  the  septum;  2,  the  internal  or  septal  twig  of  the  nasal  branch  of  the  ophthalmic  nerve;  3, 
naso-palatine  nerves.    (From  Sappy,  after  Hirschfeld  and  Leveille.) 

of  the  nasal  cavities  beneath  the  cribriform  plates  of  the  ethmoid  bones 
(Figs.  374  and  376).     The  olfactory  region  is  covered  by  cells  of  cylin- 


Fig.  375. 

Fig.  375.— Section  through  the  olfactory  mucous  membrane  of  the  new-born  child,  a,  non-nu- 
clear; and  b,  nucleated  portions  of  the  epithelium;  c,  nerves;  dd,  glands,  marked  out  by  Schultze  as 
Bowman's.    (M.  Schultzej 

Fig.  376. —Nerves  of  the  outer  walls  of  the  nasal  fossae.  3/5. — 1,  network  of  the  branches  of  the 
olfactory  nerve,  descending  upon  the  region  of  the  superior  and  middle  turbinated  bones;  2,  ex- 
ternal twig  of  the  ethmoidal  branch  of  the  nasal  nerves ;'  3,  spheno-palatine  ganglion ;  4,  ramifica- 
tion of  the  anterior  palatine  nerves ;  5,  posterior,  and  0,  middle  divisions  of  the  palatine  nerves;  7, 
branch  to  the  region  of  the  inferior  turbinated  bone;  8,  branch  to  the  region  of  the  superior  and 
middle  turbinated  bones;  9,  naso-palatine  branch  to  the  septum  cut  short.  (From  Sappey,  after 
Hirschfeld  and  Leveilltj 

drical  epithelium,  prolonged  at  their  deep  extremities  into  fine  branched 
processes,  but   not   ciliated;  and  interspersed  with  these  are  fusiform 


THE    SENSES. 


565 


{olfactory)  cells,  with  both  superficial  and  deep  processes  (Fig.  377),  the 
latter  being  probably  connected  with  the  terminal  filaments  of  the  olfac- 
tory nerve.  The  lower,  or  respiratory  part,  as  it  is  called,  of  the  nasal 
fossas  is  lined  by  cylindrical  ciliated  epithelium,  except  in  the  region  of 
the  nostrils,  where  it  is  squamous.  The  branches  of  the  olfactory  nerves 
retain  much  of  the  same  soft  and  grayish  texture  which  distinguishes 
those  of  the  olfactory  tracts  within  the  cranium.  Their  filaments,  also, 
are  peculiar,  more  resembling  those  of  the  sympathetic  nerve  than  the 
filaments  of  the  other  cerebral  nerves  do,  containing  no  outer  white  sub- 
stance, and  being  finely  granular  and  nucleated.  The  sense  of  smell  is 
derived  exclusively  through  those  parts  of  the  nasal  cav- 
ities in  which  the  olfactory  nerves  are  distributed;  the 
accessory  cavities  or  sinuses  communicating  with  the 
nostrils  seem  to  have  no  relation  to  it.  Air  impreg- 
nated with  the  vapor  of  camphor  was  injected  into  the 
frontal  sinus  through  a  fistulous  opening  and  odorous 
substances  have  been  injected  into  the  antrum  of  High- 
more;  but  in  neither  case  was  any  odor  perceived  by  the 
patient.  The  purposes  of  these  sinuses  appear  to  be, 
that  the  bones,  necessarily  large  for  the  action  of  the 
muscles  and  other  parts  connected  with  them,  may  be 
as  light  as  possible,  and  that  there  may  be  more  room 
for  the  resonance  of  the  air  in  vocalizing.  The  former 
purpose,  which  is  in  other  bones  obtained  by  filliug  their 
cavities  with  fat,  is  here  attained,  as  it  is  in  many  bones 
of  birds,  by  their  being  filled  with  air. 

Other  Functions  of  the  Olfactory  Region. — 
All  parts  of  the  nasal  cavities,  whether  or  not  they  can 
be  the  seats  of  the  sense  of  smell,  are  endowed  with  com- 
mon sensibility  by  the  nasal  branches  of  the  first  and  sec- 
'Ond  divisions  of  the  fifth  nerve.  Hence  the  sensations 
of  cold,  heat,  itching,  tickling,  and  pain;  and  the  sensation  of  tension  or 
pressure  in  the  nostrils.  That  these  nerves  cannot  perform  the  function  of 
the  olfactory  nerves  is  proved  by  cases  in  which  the  sense  of  smell  is  lost, 
while  the  mucous  membrane  of  the  nose  remains  susceptible  of  the  vari- 
ous modifications  of  common  sensation  or  touch.  But  it  is  often  difficult 
to  distinguish  the  sensation  of  smell  from  that  of  mere  feeling,  and  to 
ascertain  what  belongs  to  each  separately.  This  is  the  case  particularly 
with  the  sensations  excited  in  the  nose  by  acrid  vapors,  as  of  ammonia, 
horse-radish,  mustard,  etc.,  which  resemble  much  the  sensations  of  the 
nerves  of  touch;  and  the  difficulty  is  the  greater,  when  it  is  remembered 
that  these  acrid  vapors  have  nearly  the  same  action  upon  the  mucous 
membrane  of  the  eyelids.  It  was  because  the  common  sensibility  of  the 
nose  to  these  irritating  substances  remained  after  the  destruction  of  the 


Fig.  377.— Epithe- 
lial and  olfactory 
cells  of  man.  The 
letters  are  placed 
on  the  free  surface, 
EE,  epithelial  cells; 
Olf.,  olfactory  cells. 
(Max  Seluiltze. ) 


566  HANDBOOK    OF    PHYSIOLOGY. 

olfactory  nerves,  that  Magendie  was  led  to  the  erroneous  belief  that  the 
fifth  nerve  might  exercise  this  special  sense. 

Varieties  of  Odorous  Sensations. — Animals  do  not  all  equally  perceive 
the  same  odors;  the  odors  most  plainly  perceived  by  an  herbivorous  ani- 
mal and  by  a  carnivorous  animal  are  different.  The  Carnivora  have  the 
power  of  detecting  most  accurately  by  the  smell  the  special  peculiarities 
of  animal  matters,  and  of  tracking  other  animals  by  the  scent;  but  have 
apparently  very  little  sensibility  to  the  odors  of  plants  and  flowers.  Her- 
bivorous animals  are  peculiarly  sensitive  to  the  latter,  and  have  a  nar- 
rower sensibility  to  animal  odors,  especially  to  such  as  proceed  from  other 
individuals  than  their  own  species.  Man  is  far  inferior  to  many  animals 
of  both  classes  in  respect  of  the  acuteness  of  smell;  but  his  sphere  of  sus- 
ceptibility to  various  odors  is  more  uniform  and  extended.  The  cause 
of  this  difference  lies  probably  in  the  endowments  of  the  cerebral  parts 
of  the  olfactory  apparatus.  The  delicacy  of  the  sense  of  smell  is  most 
remarkable;  it  can  discern  the  presence  of  bodies  in  quantities  so  minute 
as  to  be  undiscoverable  even  by  spectrum  analysis;  to Tolo-ffoo-  °f  a  grain 
of  musk  can  be  distinctly  smelt  (Valentin).  Opposed  to  the  sensation 
of  an  agreeable  odor  is  that  of  a  disagreeable  or  disgusting  odor,  which 
corresponds  to  the  sensations  of  pain,  dazzling  and  disharmony  of  colors, 
and  dissonance  in  the  other  senses.  The  cause  of  this  difference  in  the 
effect  of  different  odors  is  unknown;  but  this  much  is  certain,  that  odors 
are  pleasant  or  offensive  in  a  relative  sense  only,  for  many  animals  pass 
their  existence  in  the  midst  of  odors  which  to  us  are  highly  disagreeable. 
A  great  difference  in  this  respect  is,  indeed,  observed  amongst  men: 
many  odors,  generally  thought  agreeable,  are  to  some  persons  intolerable, 
and  different  persons  describe  differently  the  sensations  that  they  sever- 
ally derive  from  the  same  odorous  substances.  There  seems  also  to  be 
in  some  persons  an  insensibility  to  certain  odors,  comparable  with  that 
of  the  eye  to  certain  colors;  and  among  different  persons,  as  great  a  dif- 
ference in  the  acuteness  of  the  sense  of  smell  as  among  others  in  the 
acuteness  of  sight.  We  have  no  exact  proof  that  a  relation  of  harmony 
and  disharmony  exists  between  odors  as  between  colors  and  sounds; 
though  it  is  probable  that  such  is  the  case,  since  it  certainly  is  so  with 
regard  to  the  sense  of  taste;  and  since  such  a  relation  would  account  in 
some  measure  for  the  different  degrees  of  perceptive  power  in  different, 
persons;  for  as  some  have  no  ear  for  music  (as  it  is  said),  so  others  have 
no  clear  appreciation  of  the  relation  of  odors,  and  therefore  little  plea- 
sure in  them. 

Subjective  Sensations. — The  sensations  of  the  olfactory  nerves,  inde- 
pendent of  the  external  application  of  odorous  substances,  have  hitherto 
been  little  studied..  The  friction  of  the  electric  machine  produces  a 
smell  like  that  of  phosphorus.  Ritter,  too,  has  observed,  that  when  gal- 
vanism is  applied  to  the  organ  of  smell,   besides  the  impulse  to  sneeze,. 


THE    SENSES; 


567 


and  the  tickling  sensation  excited  in  the  filaments  of  the  fifth  nerve,  a 
smell  like  of  ammonia  was  excited  by  the  negative  pole,  and  an  acid 
odor  by  the  positive  pole;  whichever  of  these  sensations  were  produced, 
it  remained  constant  as  long  as  the  circle  was  closed,  and  changed  to  the 
other  at  the  moment  of  the  circle  being  opened.  Subjective  sensations 
occur  frequently  in  connection  with  the  sense  of  smell.  Frequently  a 
person  smells  something  which  is  not  present,  and  which  other  persons 
cannot  smell;  this  is  very  frequent  with  nervous  people,  but  it  occasion- 
ally happens  to  every  one.  In  a  man  who  was  constantly  conscious  of  a 
bad  odor,  the  arachnoid  was  found  after  death  to  be  beset  with  deposits 
of  bone;  and  in  the  middle  of  the  cerebral  hemispheres  were  scrofulous 
cysts  in  a  state  of  suppuration.  Dubois  was  acquainted  with  a  man  who, 
ever  after  a  fall  from  his  horse,  which  occurred  several  years  before  his 
death,  believed  that  he  smelt  a  bad  odor. 

IV. — Hearing. 

Anatomy  of  the  Ear. — For  descriptive  purposes,  the  Ear,  or  Organ 
of  Hearing,  is  divided  into  three  parts,  (1)  the  external,  (2)  the  middle, 


Fig.  373— Diagrammatic  view  from  before  of  the  parts  composing  the  organ  of  hearing:  of  the 
leftside.  The  temporal  bone  of  the  left  side,  with  the  accompanying  softparts,  has  been  detach- 
ed from  the  head,  and  a  section  has  bi>en  carried  through  it  transversely,  so  as  to  remove  the  front 
of  the  meatus  extemus,  half  the  tympanic  membrane,  the  upper  and  anterior  wall  of  the  tympanum 
and  Eustachian  tube.  Ths  meatus  internua  has  also  beeu  opened,  and  the  bony  labyriul  6  exposed 
by  the  removal  of  l^e  surrounding  parts  of  the  petrous  bone,  1,  the  pinna  and  lobe;  8,  2',  meatus 
extemus;  2',  membrana  tympani;  S,  cavity  of  the  tympanum:  8',  its  opening  backwards  into  the 
mastoid  cells;  between  3  and  3',  the  chain  of  small  bouts;  4,  Eustachian  tube:  6,  meatus  interims, 
containing  the  facial  (uppermost)  and  the  auditory  nerves;  <;.  placed  on  the  vestibule  of  the  laby- 
rinth above  the  fenestra  ovalis;  r»,  apex  of  the  petrous  hone:  b,  internal  carotid  artery:  c,  styloid 
process:  tf,  facial  nerve  Issuing  from  the  stylomastoid  foramen;  e,  mastoid  process; '/,  squamous 
part  of  the  bone  covered  by  integument,  etc.    (Arnold.  I 


o68  HANDBOOK    OF  PHYSIOLOGY. 

and  (3)  the  internal  ear.  The  two  first  are  only  accessory  to  the  third 
or  internal  ear,  which  contains  the  essential  parts  of  an  organ  of  hearing. 
The  accompanying  figure  shows  very  well  the  relation  of  these  divisions 
—one  to  the  other  (Fig.  378). 

(1)  External  Ear. — The  external  ear  consists  of  the  pinna  or  auri- 
cle, and  the  external  auditory  canal  or  meatus. 

The  principal  parts  of  the  pinna  (Fig.  379)  are  two  prominent  rims 
inclosed  one  within  the  other  (helix  and  antihelix),  and  inclosing  a  cen- 
tral hollow  named  the  concha;  in  front  of  the  concha,  a  prominence  di- 
rected backwards,  the  tragus,  and  opposite  to  this  one  directed  forwards, 
the  antitragus.  From  the  concha,  the  auditory  canal,  with  a  slight  arch 
directed  upwards,  passes  inwards  and  a  little  forwards  to  the  membrana 
tympani,  to  which  it  thus  serves  to  convey  the  vibrating  air.  Its  outer 
part  consists  of  fibro-cartilage  continued  from  the  concha;  its  inner  part 
of  bone.  Both  are  lined  by  skin  continuous  with  that  of  the  pinna,  and 
extending  over  the  outer  part  of  the  membrana  tympani. 

Towards  the  outer  part  of  the  canal  are  fine  hairs  and  sebaceous 
glands,  while  deeper  in  the  canal  are  small  glands,  resembling  the  sweat- 
glands  in  structure  which  secrete  a  peculiar  yellow  substance  called  ceru- 
men, or  ear-wax. 

(2.)  Middle  Ear  or  Tympanum. — The  middle  ear,  or  tympanum 
(3,  Fig.  378),  is  separated  by  the  membrana  tympani  from  the  external 
auditory  canal.  It  is  a  cavity  in  the  temporal  bone,  opening  through 
its  anterior  and  inner  wall  into  the  Eustachian  tube,  a  cylindriform 
flattened  canal,  dilated  at  both  ends,  composed  partly  of  bone  and  partly 
of  cartilage,  and  lined  with  mucous  membrane,  which  forms  a  commu- 
nication between  the  tympanum  and  the  pharynx.  It  opens  into  the 
cavity  of  the  pharynx  just  behind  the  posterior  aperture  of  the  nostrils. 
The  cavity  of  the  tympanum  communicates  posteriorly  with  air-cavities, 
the  mastoid  cells  in  the  mastoid  process  of  the  temporal  bone,  but  its 
only  opening  to  the  external  air  is  through  the  Eustachian  tube  (4,  Fig. 
378).  The  walls  of  the  tympanum  are  osseous,  except  where  apertures 
in  them  are  closed  with  membrane,  as  at  the  fenestra  rotunda,  and  fe- 
nestra ovalis,  and  at  the  outer  part  where  the  bone  is  replaced  by  the 
membrana  tympani.  The  cavity  of  the  tympanum  is  lined  with  mucous 
membrane,  the  epithelium  of  which  is  ciliated  and  continuous  with  that 
of  the  pharynx.  It  contains  a  chain  of  small  bones  (ossicula  auditus) 
which  extends  from  the  membrana  tympani  to  the  fenestra  ovalis.  . 

The  Membrana  Tympani  is  placed  in  a  slanting  direction  at  the 
bottom  of  the  external  auditory  canal,  its  plane  being  at  an  angle  of 
about  45°  with  the  lower  wall  of  the  canal.  It  is  formed  chiefly  of  a 
tough  and  tense  fibrous  membrane,  the  edges  of  which  are  set  in  a  bony 
groove;  its  outer  surface  is  covered  with  a  continuation  of  the  cutaneous 
lining  of  the  auditory  canal,  its  inner  surface  with  part  of  the  ciliated 
mucous  membrane  of  the  tympanum. 


THE    SENSES. 


569 


The  ossicles  or  small  bones  of  the  ear  are  three,  named  Malleus, 
Incus,  and  Stapes.  The  Malleus,  or  hammer-bone,  is  attached  by  u 
long,  slightly-curved  process,  called  its  handle,  to  the  membrana  tym- 
pani;  the  line  of  attachment  being  vertical,  includ- 
ing the  whole  length  of  the  handle,  and  extending 
from  the  upper  border  to  the  centre  of  the  mem- 
brane. The  head  of  the  malleus  is  irregularly 
rounded;  its  neck,  or  the  line  of  boundary  between 
it  and  the  handle,  supports  two  processes;  a  short 
conical  one,  which  receives  the  insertion  of  the 
tensor  tympani,  and  a  slender  one,  processus  gra- 
cilis, which  extends  forwards,  and  to  which  the 
laxator  tympani  muscle  is  attached.  The  incus, 
or  anvil-bone,  shaped  like  a  bicuspid  molar  tooth, 
is  articulated  by  its  broader  part,  corresponding 
with  the  surface  of  the  crown  of  a  tooth,  to  the 
malleus.  Of  its  two  fang-like  processes,  one,  di- 
rected backwards,  has  a  free  end  lodged  in  a  de- 
pression in  the  mastoid  bone;  the  other,  curved 
downwards  and  more  pointed,  articulates  by  means 
of  a  roundish  tubercle,  formerly  called  os  orbicu- 
lare,  with  the  stapes,  a  little  bone  shaped  exactly 
like  a  stirrup,  of  which  the  base  or  bar  fits  into  the 
fenestra  ovalis.  To  the  neck  of  the  stapes,  a  short 
process,  corresponding  with  the  loop  of  the  stir- 
rup, is  attached  the  stapedius  muscle. 

"The  ossicula  of  aquatic  mammalia  are  very  bulky  and  relatively 
large,  especially  in  the  true  seals  and  the  sireuia  (Manatee  and  Dugong). 
Ju  the  cetacea  the  stapes  is  generally  ankylosed  to  the  fenestra  ovalis. 
the  malleus  is  always  ankylosed  to  the  tympanic  bone,  yet  the  membrana 


Fig.  379.— Outer  sur- 
face of  the  pinna  of  the 
right  auricle.  1,  helix;  -J, 
fossa  of  the  helix;  3,  anti- 
helix;  4,  fossa  of  the  au- 
tihelix;  5,  antitragus;  6, 
tragus;  7,  concha;  8, 
lobule.    '-.•. . 


Fig.  380. 


Fig.  381. 


■>-1 


Fig.  382. 


Fig.  380  —The  hammer-bone  or  malleus,  seen  from  the  front.   1,  The  head ;  2,  neck ;  3,  short  pro- 
cess; 4,  long  process.    (Schwalbe.) 

Fig.  3S1.— The  incus,  or  anvil-bone.    1,  body:  2.  ridged  articulation  forthe  malleus;  \,  processus 
brevis,  with  5,  rough  articular  surface  for  ligament  of  incus;  (i,  processus  magnus,  with  articulal 
ing  surface  for  stapes;  7,  nutrient  foramen.    < Schwalbe.  I 

Fig.  382. — The  stapes,  or  stirrup-bone.    1,  base;  2  and  3,  arch;  4,  head  of  bone,  which  articulates 
with  orbicular  process  of  the  incus;  5,  constricted  part  of  neck;  6,  one  of  the  crura.    (Schwalbe.  i 


tympani  is  well  formed,  and  there  is  a  manubrium,  often  ill-developed, 
but  always  attached  to  the  membrane  by  a  long  process.  In  the  Otarisa  or 
Sea-lions,  where  the  ossicula  are  far  smaller  relatively,  and  less  solid  than 
in  whales,  manatees,  and  the  earless  true  seals,  there  are  well-formed, 


570 


HANDBOOK    OF    PHYSIOLOGY 


movable  external  ears.  The  ossicula  seem  to  be  vestigial  relics  utilized 
for  the  auditory  function.  In  land  animals  they  vary  in  shape  accord- 
ing to  the  type  of  the  animal  rather  than  in  relation  to  its  acuteness  of 
hearing.  I  have  never  found  a  muscular  laxator  tympani  in  any  ani- 
mal, but  the  tensor  exists  as  a  ligament  in  whales  where  the  malleus  is 
fixed."     (Alban  Doran.) 

The  bones  of  the  ear  are  covered  with  mucous  membrane  reflected  over 
them  from  the  wall  of  the  tympanum;  and  are  movable  both  altogether 
and  one  upon  the  other.  The  malleus  moves  and  vibrates  with  every 
movement  and  vibration  of  the  membrana  tympani,  and  its  movements 
are  communicated  through  the  incus  to  the  stapes,  and  through  it  to  the 
membrane  closing  the  fenestra  ovalis.  The  malleus,  also,  is  movable 
in  its  articulation  with  the  incus;  and  the  membrana  tympani  moving 
with  it  is  altered  in  its  degree  of  tension  by  the  laxator  and  tensor  tym- 
pani muscles.  The  stapes  is  movable  on  the  process  of  the  incus,  when 
the  stapedius  muscle  acting,  draws  itbackwards.  The  axis  round  which 
the  malleus  and  incus  rotate  is  the  line  joining  the  processus  gracilis  of 
the  malleus  and  the  posterior  (short)  process  of  the  incus. 


Fig.  383.— Interior  view  of  the  tympanum,  with  membrana  tympani  and  bones  in  natural  posi- 
tion. 1,  Membrana  tympani;  2,  Eustachian  tube;  3,  tensor  tympani  muscle;  4,  lig.  mallei  superior; 
5,  lig.  mallei  super. ;  6,  chorda-tympanic  nerve;  a,  b,  and  c,  sinuses  about  ossicula.     (Schwalbe.j 

(3.)  The  Internal  Ear. — The  proper  organ  of  hearing  is  formed 
by  the  distribution  of  the  auditory  nerve  within  the  internal  ear,  or 
labyrinth,  a  set  of  cavities  within  the  petrous  portion  of  the  temporal 
bone.  The  bone  which  forms  the  walls  of  these  cavities  is  denser  than 
that  around  it,  and  forms  the  osseous  labyrinth  ;  the  membrane  within 
the  cavities  forms  the  membranous  labyrinth.  The  membranous  laby- 
rinth contains  a  fluid  called  endolymph  ;  while  outside  it,  between  it  and 
the  osseous  labyrinth,  is  a  fluid  called  perilymph. 

The  osseous  labyrinth  consists  of  three  principal  parts,  namely,  the 
vestibule,  the  cochlea,  and  the  semicircular  canals. 

The  Anatomy  of  the  Internal  Ear. — The  vestibule  is  the  middle 
cavity  of  the  labyrinth,  and  the  central  organ  of  the  whole  auditory  ap- 


THE     SENSES.  o7l 

paratuB.  It  presents,  in  its  inner  wall,  several  openings  for  the  entrance 
of  the  divisions  of  the  auditory  nerve;  in  its  outer  wall,  the  fenestra 
oralis  (2,  Fig.  384),  an  opening  filled  by  the  base  of  the  stapes,  one  of 
the  small  bones  of  the  ear;  in  its  j:>osterior  and  superior  walls,  five  open- 
ings by  which  the  semicircular  canals  communicate  with  it:  in  its  ante- 
rior wall,  an  opening  leading  into  the  cochlea.  The  hinder  part  of  the 
inner  wall  of  the  vestibule  also  presents  an  opening,  the  orifice  of  the 
aqnceductus  vestibuli,  a  canal  leading  to  the  posterior  margin  of  the 
petrous  bone,  with  uncertain  contents  and  unknown  purpose. 

The  semicircular  canals  (Figs.  384,  385),  are  three  arched  cylin- 
driform  bony  canals,  set  in  the  substance  of  the  petrous  bone.  They  all 
open  at  both  ends  into  the  vestibule  (two  of  them  first  coalescing).  The 
ends  of  each  are  dilated  just  before  opening  into  the  vestibule;  and  one 
end  of  each  being  more  dilated  than  the  other  is  called  an  ampulla. 
Two  of  the  canals  form  nearly  vertical  arches;  of  these  the  superior  is 
also  anterior;  the  posterior  is  inferior;  the  third  canal  is  horizontal,  and 
lower  and  shorter  than  the  others. 


Fig.  364. 


Fig.  385. 


Fig.  384.— Right  bony  labyrinth,  viewed  from  the  outer  side.  The  specimen  here  representerl  is 
prepared  by  separating"piecemeal  the  looser  substance  of  the  petrous  bone  from  the  dense  walls 
which  immediately  inclose  the  labyrinth.  1,  the  vestibule;  2,  fenestra  ovalis;  S,  superior  semicir- 
cular canal;  4,  horizontal  or  external  canal;  5,  posterior  canal;  *,  ampullae  of  the  semicircular 
canals;  6,  first  turn  of  the  cochlea;  7,  second  turn;  8,  apex;  9,  fenestra  rotunda.  The  smaller  fig- 
ure in  outline  below  shows  the  natural  size.    2J^/1.    (Siimmering. ) 

Fig.  385.— View  of  the  interior  of  the  left  labyrinth.  The  bony  wall  of  the  labyrinth  is  removed 
superiorly  and  externally.  1,  fovea  hemielliptica;  2,  fovea  hemispherica;  3.  common  opening  of 
the  superior  and  posterior  semicircular  canals;  4,  opening  of  the  aqueduct  of  the  vestibule:  5.  the 
superior,  6,  the  posterior,  and  7,  the  external  semicircular  canals;  8,  spiral  tube  of  the  cochlea 
i  scala  tympani);  9,  opening  of  the  aqueduct  of  the  cochlea;  10,  placed  on  the  lamina  spiralis  in  the 
scala  vestibuli.     2„\./l.    (Summering..) 

The  cochlea  (G,  7,  8,  Figs.  384  and  385),  a  small  organ,  shaped  like 
a  common  snail-shell,  is  seated  in  front  of  the  vestibule,  its  base  resting 
on  the  bottom  of  the  internal  meatus,  where  some  apertures  transmit  to 
it  the  cochlear  filaments  of  the  auditory  nerve.  In  its  axis,  the  cochlea 
is  traversed  by  a  conical  column,  the  modiolus,  around  which  a  spiral 
canal  winds  with  about  two  turns  and  a  half  from  the  base  to  the  apex. 
At  the  apex  of  the  cochlea  the  canal  is  closed;  at  the  base  it  presents 
three  openings,  of  which  one,  already  mentioned,  communicates  with  the 
vestibule;  another  called  fenestra  rotunda,  is  separated  by  a  mem- 
brane from  the  cavity  of  the  tympanum;    the  third  is  the  orifice  of  the 


£-79 


HANDBOOK    OF    PHYSIOLOGY. 


aquceduclus  coclileai,  a  canal  leading  to  the  jugular  fossa  of  the  petrous 
bone,  and  corresponding,  at  least  in  obscurity  of  purpose  and  origin,  to 
the  aquaeductus  vestibuli.  The  spiral  canal  is  divided  into  two  passages, 
■or  scalas,  by  a  partition  of  bone  and  membrane,  the  lamina  spiralis. 
The  osseous  part  or  zone  of  this  lamina  is  connected  with  the  modiolus; 
the  membranous  part,  with  a  muscular  zone,  forming  its  outer  margin, 
is  attached  to  the  outer  wall  of  the  canal.  Commencing  at  the  base  of 
the  cochlea,  between  its  vestibular  and  tympanic  openings,  they  form  a 
partition  between  these  apertures;  the  two  scalae  are,  therefore,  in  cor- 
respondence with  this  arrangement,  named  scala  vestibuli  and  scala 
tympani  (Fig.  386).  At  the  apex  of  the  cochlea,  the  lamina  spiralis 
ends  in  a  small  hamulus,  the  inner  and  concave  part  of  which,  being  de- 
tached from  the  summit  of  the  modiolus,  leaves  a  small  aperture  named 
lielicotrema,  by  which  the  two  scalas,  separated  in  all  the  rest  of  their 
length,  communicate. 

Besides  the  scala  vestibuli  and  scala  tympani,  there  is  a  third  space 
between  them,  called  scala  media  or  canalis  membranaceus   (CO.  Fig. 


Fig.  386. 


Fig.  38? 


Fig.  386.— View  of  the  osseous  cochlea  divided  through  the  middle.  1,  central  canal  of  the 
modiolus;  2,  lamina  spiralis  ossea;  3,  scala  tympani;  4,  scala  vestibuli;  5,  porous  substance  of  the 
modioius  near  one  of  the  sections  of  the  canalis  spiralis  modioli.  5/1.  (Arnold. ) 

Fig.  387.— Section  through  one  of  the  coils  of  the  cochlea  ( diagrammatic) .  S  T,  scala  tym- 
pani; 6'  V,  scala  vestibuli;  C  C.  canalis  cochleae  or  canalis  membranaceus;  R,  membrane  of  Reiss- 
ner;  I  s  o,  (amina  spiralis  ossea;  I  I  s,  limbus  laminae  spiralis;  s  s,  sulcus  spiralis;  n  c,  cochlear 
nerve;  g  s,  ganglion  spirale;  t,  membrana  tectoria  (below  the  membrana  tectoria  is  the  lamina 
reticularis);  b,  membrana  basilaris;  Co,  rods  of  Corti ;  I  sp,  ligamentum  spirale.    (Quain.) 


387).  In  section  it  is  triangular,  its  external  wall  being  formed  by  the 
wall  of  the  cochlea,  its  upper  wall  (separating  it  from  the  scala  vesti- 
buli) by  the  membrane  of  Keissner,  and  its  lower  wall  (separating  it 
from  the  scala  tympani)  by  the  basilar  membrane,  these  two  meeting  at 
the  outer  edge  of  the  bony  lamina  spiralis.  Following  the  turns  of  the 
cochlea  to  its  apex,  the  scala  media  there  terminates  blindly;  while 
towards  the  base  of  the  cochlea  it  is  also  closed  with  the  exception  of  a 
very  narrow  passage  (canalis  reuniens)  uniting  it  with  the  sacculus.  The 
scala  media  (like  the  rest  of  the  membranous  labyrinth)  contains  endo- 
lymph. 

Organ  of  Corti. — Upon  the  basilar  membrane  are  arranged  cells  of 
various  shapes. 

About  midway  between  the  outer  edge  of  the  lamina  spiralis  and  the 
outer  wall  of  the  cochlea  are  situated  the  rods  of  Corti.     Viewed  side- 


THE    SENSES. 


573 


ways,  the  rods  of  Corti  are  seen  to  consist  of  an  external  and  internal 
pillar,  each  rising  from  an  expanded  foot  or  base  on  the  basilar  mem- 
brane (o,  n.  Fig.  388).  They  slant  inwards  towards  each  other,  and 
each  ends  in  a  swelling  termed  the  head;  the  head  of  the  inner  pillar 
overlying  that  of  the  outer  (Fig.  388).  Each  pair  of  pillars  forms,  as  it 
were,  a  pointed  roof  arching  over  a  space,  and  by  a  succession  of  them, 
a  little  tunnel  is  formed. 

It  has  been  estimated  that  there  are  about  3,000  of  these  pairs  of  pil- 
lars, in  proceeding  from  the  base  of  the  cochlea  towards  its  apex.  They 
are  found  progressively  to  increase  in  length,  and  become  more  oblique; 
in  other  words  the  tunnel  becomes  wider,  but  diminishes  in  height  as  we 
approach  the  apex  of  the  cochlea.  Leaning,  as  it  were,  against  these 
external  and  internal  pillars  are  certain  other  cells,  of  which  the  exter- 
nal ones,  hair  cells,  terminate  in  small  hair-like  processes.  Most  of  the 
above  details  are  shown  in  the  accompanying  figure  (Fig.    388).     This 


Fig.  388.— Vertical  section  of  the  organ  of  Corti  from  the  dog.  1  to  2,  homogeneous  layer  of  the 
so-called  membrana  basilaris;  u,  vestibular  layer;  v,  tympanal  layer,  with  nuclei  and  protoplasm; 
a,  prolongation  of  tympanal  periosteum  of  lamina  spiralis  ossea;  c,  thickened  commencement  or 
the  membrana  basilaris  near  the  point  of  perforation  of  the  nerves  h  ■  d,  blood-vessel  ( vas  spirale  I : 
e.  blood-vessel;  /,  nerves;  g,  the  epithelium  of  the  sulcus  spiralis  iuternus.  i,  internal  or  tufted  cell, 
with  basil  process  /,-,  surrounded  with  nuclei  and  protoplasm  (of  the  granular  layer),  into  which  tin- 
nerve- fibres  radiate;  I,  hairs  of  the  internal  hair-cell;  n .  base  or  foot  of  the  inner  pillar  of  organ  of 
Corti;  mx  head  of  the  same  uniting  with  the  corresponding  part  of  an  external  pillar,  whose  under 
half  is  missing,  while  the  next  pillar  beyond,  o.  presents  both  middle  portion  and  base;  ?-.  s,  <1.  three 
external  hair  cells;  t,  bases  of  two  neighboring  hair  or  tufted  cells;  as,  so-called  supporting  cell  of 
Hensen;  w,  nerve-fibre  terminating  in  the  first  of  the  external  hair-cells;  II  to  I.  lamina  reticularis. 
X  800.    (Waldeyerj 


complicated  structure  rests,  as  we  have  seen,  upon  the  basilar  membrane, 
it  is  roofed  in  by  a  remarkable  fenestrated  membrane  or  lamina  reticu- 
laris into  the  fenestra?  of  which  the  tops  of  the  various  rods  and  cells  are 
received.  When  viewed  from  above,  the  organ  of  Corti  shows  a  remark- 
able resemblance  to  the  key-board  of  a  piano.  In  close  relation  with  the 
rods  of  Corti  and  the  cells  inside  and  outside  them,  and  probably  pro- 
jecting by  free  ends  into  the  little  tuunel  containing  fluid  (roofed  in  by 
them),  are  filaments  of  the  auditory  nerve. 

Membranous  Labyrinth. — This  corresponds  generally  with  the 
form  of  the  osseous  labyrinth,  so  far  as  regards  the  vestibule  and  semicir- 
cular canals,  but  is  separated  from  the  walls  of  these  parts  by  fluid  (en- 
dolymph),   except  where  the  nerves  enter  into   connection   within   it. 


574  HANDBOOK    OF    PHYSIOLOGY. 

Betweeu  its  outer  surface  and  the  inner  surface  of  the  walls  of  the  vesti- 
bule and  semicircular  canals  is  another  collection  of  similar  fluid,  called 
perilymph:  so  that  all  the  sonorous  vibrations  impressing  the  auditory 
nerves  on  these  parts  of  the  internal  ear,  are  conducted  through  fluid  to 
a  membrane  suspended  in  and  containing  fluid.  In  the  cochlea,  the 
membranous  labyrinth  completes  the  septum  between  the  two  scalce,  and 
incloses  a  spiral  canal,  previously  mentioned,  called  canalis  membrana- 
ceus  or  canalis  cochlear  (Fig.  387).  The  fluid  in  the  scalce  of  the  coch- 
lea is  continuous  with  the  perilymph  in  the  vestibule  and  semicircular 
canals,  and  there  is  no  fluid  external  to  its  lining  membrane.  The  ves- 
tibular portion  of  the  membranous  labyrinth  comprises  two,  probably 
communicating  cavities,  of  which  the  larger  and  upper  is  named  the 
utriculus;  the  lower,  the  sacculus.  They  are  lodged  in  depressions  in 
the  bony  labyrinth  termed  respectively  "fovea  hemielliptica"  and 
"fovea  hemispherica."  Into  the  former  open  the  orifices  of  the  mem- 
branous semicircular  canals;  into  the  latter  the  canalis  cochlece.  The 
membranous  labyrinth  of  all  these  parts  is  laminated,  transparent,  very 
vascular,  and  covered  on  the  inner  surface  with  nucleated  cells,  of  which 
those  that  line  the  ampullae  are  prolonged  into  stiff  hair-like  processes; 
the  same  appearance,  but  to  a  much  less  degree,  being  visible  in  the  utri- 
citle  and  saccule.  In  the  cavities  of  the  utriculus  and  sacculus  are  small 
masses  of  calcareous  particles,  otoconia  or  otoliths;  and  the  same,  although 
in  more  minute  quantities,  are  to  be  found  in  the  interior  of  some  other 
parts  of  the  membranous  labyrinth. 

Auditory  Nerve.— For  the  appropriate  exposure  of  the  filaments  of 
the  auditory  nerve  to  sonorous  vibrations  all  the  organs  now  described 
are  provided.  It  is  characterized  as  a  nerve  of  special  sense  by  its  soft- 
ness (whence  it  derived  its  name  of  portio  mollis  of  the  seventh  pair), 
and  by  the  fineness  of  its  component  fibres.  It  enters  the  labyrinth  of 
the  ear  in  two  divisions;  one  for  the  vestibule  and  semicircular  canals, 
and  the  other  for  the  cochlea. 

The  branches  for  the  vestibule  spread  out  and  radiate  on  the  inner 
surface  of  the  membranous  labyrinth:  their  exact  termination  is  un- 
known. Those  for  the  semicircular  canals  pass  into  the  ampullae,  and 
form,  within  each  of  them,  a  forked  projection  which  corresponds  with 
a  septum  in  the  interior  of  the  ampulla.  The  branches  for  the  cochlea 
enter  it  through  orifices  at  the  base  of  the  modiolus,  which  they  ascend. 
and  thence  successively  pass  into  canals  in  the  osseous  part  of  the  lamina 
spiralis.  In  the  canals  of  this  osseous  part  or  zone,  the  nerves  are  arranged 
in  a  plexus,  containing  ganglion  cells.  Their  ultimate  termination  is  not 
known  with  certainty;  but  some  of  them,  without  doubt,  end  in  the 
organ  of  Corti,  probably  in  cells. 


THE    .SENSES.  575 


Physiology  of  Hearing. 

All  the  acoustic  contrivances  of  the  organ  of  hearing  are  means  for 
conducting  sound,  just  as  the  optical  apparatus  of  the  eye  are  media  for 
conducting  light.  Since  all  matter  is  capable  of  propagating  sonorous 
vibrations,  the  simplest  conditions  must  be  sufficient  for  mere  hearing; 
for  all  substances  surrounding  the  auditory  nerve  would  communicate 
sound  to  it.  The  whole  development  of  the  organ  of  hearing,  therefore, 
can  have  for  its  object  merely  the  rendering  more  perfect  the  propaga- 
tion of  the  sonorous  vibrations,  and  their  multiplication  by  resonance; 
and,  in  fact,  all  the  acoustic  apparatus  of  the  organ  may  be  shown  to 
have  reference  to  these  two  principles. 

Functions  of  the  External  Ear. — The  external  auditory  passage 
influeiices  the  propagation  of  sound  to  the  tympanum  in  three  ways: — 
1,  by  causing  the  sonorous  undulations,  entering  directly  from  the  atmo- 
sphere, to  be  transmitted  by  the  air  in  the  passage  immediately  to  the 
membrana  tympani,  and  thus  preventing  them  from  being  dispersed;  2, 
by  the  walls  of  the  passage  conducting  the  sonorous  undulations  im- 
parted to  the  external  ear  itself,  by  the  shortest  path  to  the  attachment 
of  the  membrana  tympani,  and  so  to  this  membrane;  3,  by  the  resonance 
of  the  column  of  air  contained  within  the  passage;  4,  the  external  ear, 
especially  when  the  tragus  is  provided  with  hairs,  is  also,  doubtless,  of 
service  in  protecting  the  meatus  and  membrana  tympani  against  dust, 
insects,  and  the  like. 

1.  As  a  conductor  of  undulations  of  air,  the  external  auditory  pas- 
sage receives  the  direct  undulations  of  the  atmosphere,  of  which  those 
that  enter  in  the  direction  of  its  axis  produce  the  strongest  impressions. 
The  undulations  which  enter  the  passage  obliquely  are  reflected  by  its 
parietes,  and  thus  by  reflexion  reach  the  membrana  tympani. 

2.  The  walls  of  the  meatus  are  also  solid  conductors  of  sound;  for 
those  vibrations  which  are  communicated  to  the  cartilage  of  the  external 
ear,  and  not  reflected  from  it,  are  propagated  by  the  shortest  path  through 
the  parietes  of  the  passage  to  the  membrana  tympani.  Hence,  both  ears 
being  close  stopped,  the  sound  of  a  pipe  is  heard  more  distinctly  when 
its  lower  extremity,  covered  with  a  membrane,  is  applied  to  the  cartilage 
of  the  external  ear  itself,  than  when  it  is  placed  in  contact  with  the  sur- 
face of  the  head. 

3.  The  external  auditory  passage  is  important,  inasmuch  as  the  air 
which  it  contains,  like  all  insulated  masses  of  air,  increases  the  intensity 
of  sounds  by  resonance. 

Regarding  the  cartilage  of  the  external  ear,  therefore,  as  a  conductor 
of  sonorous  vibrations,  all  its  inequalities,  elevations,  and  depressions, 
which  are  useless  with  regard  to  reflexion,  become  of  evident  importance; 
for  those  elevations  and  depressions  upon  which  the  undulations  fall 
perpendicularly,  will  be  affected  by  them  in  the  most  intense  degree; 


576  HANDBOOK    OF    PHYSIOLOGY. 

and,  in  consequence  of  the  various  form  and  position  of  these  inequali- 
ties, sonorous  undulations,  in  whatever  direction  they  may  come,  must 
fall  perpendicularly  upon  the  tangent  of  some  one  of  them.  This  affords 
an  explanation  of  the  extraordinary  form  given  to  this  part. 

Functions  of  the  Middle  Ear. — In  animals  living  in  the  atmo- 
sphere, the  sonorous  vibrations  are  conveyed  to  the  auditory  nerve  by 
three  different  media  in  succession,  namely,  the  air,  the  solid  parts  of 
the  body  of  the  animal  and  of  the  auditory  apparatus,  and  the  fluid  of 
the  labyrinth.  Sonorous  vibrations  are  imparted  too  imperfectly  from 
air  to  solid  bodies,  for  the  propagation  of  sound  to  the  internal  ear  to  be 
adequately  effected  by  that  means  alone;  yet  already  an  instance  of  its 
being  thus  propagated  has  been  mentioned.  In  passing  from  air  directly 
into  water,  sonorous  vibrations  suffer  also  a  considerable  diminution  of 
their  strength;  but  if  a  tense  membrane  exists  between  the  air  and  the 
water,  the  sonorous  vibrations  are  communicated  from  the  former  to  the 
latter  medium  with  very  great  intensity.  This  fact,  of  which  Muller 
gives  experimental  proof,  furnishes  at  once  an  explanation  of  the  use  of 
the  fenestra  rotunda,  and  of  the  membrane  closing  it.  They  are  the 
means  of  communicating,  in  full  intensity,  the  vibrations  of  the  air  in 
the  tympanum  to  the  fluid  of  the  labyrinth.  This  peculiar  property  of 
membranes  is  the  result,  not  of  their  tenuity  alone,  but  of  the  elasticity 
and  capability  of  displacement  of  their  particles;  and  it  is  not  impaired 
when,  like  the  membrane  of  the  fenestra  rotunda,  they  are  not  impreg- 
nated with  moisture. 

Sonorous  vibrations  are  also  communicated  without  any  perceptible 
loss  of  intensity  from  the  air  to  the  water,  when  to  the  membrane  form- 
ing the  medium  of  communication,  there  is  attached  a  short,  solid  body, 
which  occupies  the  greater  part  of  its  surface,  and  is  alone  in  contact 
with  the  water.  This  fact  elucidates  the  action  of  the  fenestra  ovalis, 
and  of  the  plate  of  the  stapes  which  occupies  it,  and,  with  the  preceding 
fact,  shows  that  both  fenestra? — that  closed  by  membrane  only,  and  that 
with  which  the  movable  stapes  is  connected — transmit  very  freely  the 
sonorous  vibrations  from  the  air  to  the  fluid  of  the  labyrinth. 

A  small,  solid  body,  fixed  in  an  opening  by  means  of  a  border  of 
membrane,  so  as  to  be  movable,  communicates  sonorous  vibrations  from 
air  on  the  one  side,  to  water,  or  the  fluid  of  the  labyrinth,  on  the  other  side, 
much  better  than  solid  media  not  so  constructed.  But  the  propagation 
of  sound  to  the  fluid  is  rendered  much  more  perfect  if  the  solid  con- 
ductor thus  occupying  the  opening,  or  fenestra  ovalis,  is  by  its  other  end 
fixed  to  the  middle  of  a  tense  membrane,  which  has  atmospheric  air  on 
both  sides.  A  tense  membrane  is  a  much  better  conductor  of  the  vibra- 
tions of  air  than  any  other  solid  body  bounded  by  definite  surfaces:  and 
the  vibrations  are  also  communicated  very  readily  by  tense  membranes  to 
solid  bodies  in  contact  with  them.     Thus,  then,  the  membrana  tympani 


THE    SENSES.  ~>7i 

serves  for  the  transmission  of  sound  from  the  air  to  the  chain  of  auditory 
bones.  Stretched  tightly  in  its  osseous  ring,  it  vibrates  with  the  air  in 
the  auditory  passage,  as  any  thin  tense  membrane  will,  when  the  air  near 
it  is  thrown  into  vibrations  by  the  sounding  of  a  tuning-fork  or  a  musi- 
cal string.  And,  from  such  a  tense  vibrating  membrane,  the  vibrations 
are  communicated  with  great  intensity  to  solid  bodies  which  touch  it  at 
any  point.  If,  for  example,  one  end  of  a  flat  piece  of  wood  be  applied  to 
the  membrane  of  a  drum,  while  the  other  end  is  held  in  the  hand,  vibra- 
tions are  felt  distinctly  when  the  vibrating  tuning-fork  is  held  over  the 
membrane  without  touching  it;  but  the  wood  alone,  isolated  from  the 
membrane,  will  only  very  feebly  propagate  the  vibrations  of  the  air  to 
the  hand. 

In  comparing  the  membrana  tympani  to  the  membrane  of  a  drum,  it 
is  necessary  to  point  out  certain  important  differences. 

When  a  drum  is  struck,  a  certain  definite  tone  is  elicited  (fundamen- 
tal tone);  similarly  a  drum  is  thrown  into  vibi'ation  when  certain  tones 
are  sounded  in  its  neighborhood,  while  it  is  quite  unaffected  by  others. 
In  other  words  it  can  only  take  up  and  vibrate  in  response  to  those  tones 
whose  vibrations  nearly  correspond  in  number  with  those  of  its  own  fun- 
damental tone.  The  tympanic  membrane  can  take  up  an  immense  range 
of  tones  produced  by  vibrations  ranging  from  30  to  4,000  or  5,000  per 
second.  This  would  be  clearly  impossible  if  it  were  an  evenly  stretched 
membrane. 

The  fact  is,  that  the  tympanic  membrane  is  by  no  means  evenly 
stretched,  and  this  is  due  partly  to  its  slightly  funnel-like  form,  and 
partly  to  its  being  connected  with  the  chain  of  auditory  ossicles.  Fur- 
ther, if  the  membrane  were  quite  free  in  iis  centre,  it  would  go  on  vibrat- 
ing as  a  drum  does  some  time  after  it  is  struck,  and  each  sound  would 
be  prolonged,  leading  to  considerable  confusion.  This  evil  is  obviated 
by  the  ear-bones,  which  check  the  continuance  of  the  vibrations  like  the 
"dampers''  in  a  pianoforte. 

The  ossicula  of  the  ear  are  the  better  conductors  of  the  sonorous  vi- 
brations communicated  to  them,  on  account  of  being  isolated  by  an 
atmosphere  of  air,  and  not  continuous  with  the  bones  of  the  cranium; 
for  every  solid  body  thus  isolated  by  a  different  medium,  propagates  vi- 
brations with  more  intensity  through  its  own  substance  than  it  commu- 
nicates them  to  the  surrounding  medium,  which  thus  prevents  a  disper- 
sion of  the  sound;  just  as  the  vibrations  of  the  air  in  the  tubes  used  for 
conducting  the  voice  from  one  apartment  to  another  are  prevented  from 
being  dispersed  by  the  solid  walls  of  the  tube.  The  vibrations  of  the 
membrana  tympaui  are  transmitted,  therefore,  by  the  chain  of  ossicula 
to  the  fenestra  ovalis  and  fluid  of  the  labyrinth,  their  dispersion  in  the 
tympanum  being  prevented  by  the  difficulty  of  the  transition  of  vibra- 
tions from  solid  to  gaseous  bodies. 

The  necessity  of  the  presence  of  air  on  the  inner  side  of  the  membrana 
tvmpani,  in  order  to  enable  it  and  the  ossicula  auditus  to  fulfil  the  ob- 
37 


578  HANDBOOK    OF    PHYSIOLOGY. 

jects  just  described,  is  obvious.  Without  this  provision,  neither  would 
the  vibrations  of  the  membrane  be  free,  nor  the  chain  of  bones  isolated, 
so  as  to  propagate  the  sonorous  undulations  with  concentration  of  their 
intensity.  But  while  the  oscillations  of  the  membrana  tympani  are 
readily  communicated  to  the  air  in  the  cavity  of  the  tympanum,  those  of 
the  solid  ossicula  will  not  be  conducted  away  by  the  air,  but  will  be  pro- 
pagated to  the  labyrinth  without  being  dispersed  in  the  tympanum. 

The  propagation  of  sound  through  the  ossicula  of  the  tympanum  to 
the  labyrinth,  must  be  effected  either  by  oscillations  of  the  bones,  or  by 
a  kind  of  molecular  vibration  of  their  particles,  or,  most  probably,  by 
both  these  kinds  of  motion. 

Movements  of  the  ossicula. — E.  Weber  has  shown  that  the  existence 
of  the  membrane  over  the  fenestra  rotunda  will  permit  approximation 
and  removal  of  the  stapes  to  and  from  the  labyrinth.  When  by  the 
stapes  the  membrane  of  the  fenestra  ovalis  is  pressed 
towards  the  labyrinth,  the  membrane  of  the  fenestra 
rotunda  may,  by  the  pressure  communicated  through 
the  fluid  of  the  labyrinth,  be  pressed  towards  the  cavity 
of  the  tympanum. 

The  long  process  of  the  malleus  receives  the  undula- 
tions of  the  membrana  tympani  (Fig.  389,  a,  a)  and  of 
the  air  in  a  direction  indicated  by  the  arrows,  nearly 
perpendicular  to  itself.  From  the  long  process  of  the 
malleus  they  are  propagated  to  its  head  (b):  thence  into 
the  incus  (c),  the  long  process  of  which  is  parallel  with 
the  long  process  of  the  malleus.  From  the  long  process 
of  the  incus  the  undulations  are  communicated  to  the 
stapes  (d)  which  is  united  to  the  incus  at  right  angles. 
The  several  changes  in  the  direction  of  the  chain  of 
fig.  389.  bones  have,  however,  no  influence  on  that  of  the  undu- 

lations, which  remains  the  same  as  it  was  in  the  meatus 
externus  and  long  process  of  the  malleus,  so  that  the  undulations  are 
communicated  by  the  stapes  to  the  fenestra  ovalis  in  a  perpendicular 
direction. 

Increasing  tension  of  the  membrana  tympani  diminishes  the  facility 
of  transmission  of  sonorous  undulations  from  the  air  to  it. 

Savart  observed  that  the  dry  membrana  tympani,  on  the  approach  of 
a  body  emitting  a  loud  sound,  rejected  particles  of  sand  strewn  upon  it 
more  strongly  when  lax  than  when  very  tense;  and  inferred,  therefore, 
that  hearing  is  rendered  less  acute  by  increasing  the  tension  of  the  mem- 
brana tympani.  Muller  has  confirmed  this  by  experiments  with  small 
membranes  arranged  so  as  to  imitate  the  membrana  tympani;  and  it  may 
be  confirmed  also  by  observations  on  one's  self. 

The  pharyngeal  orifice  of  the  Eustachian  tube  is  usually  shut;  during 
swallowing,  however,  it  is  opened;  this  may  be  shown  as  follows: — If 
the  nose  and  mouth  be  closed  and  the  cheeks  blown  out,  a  sense  of  pres- 
sure is  produced  in  both  ears  the  moment  we  swallow;  this  is  due,  doubt- 
less, to  the  bulging  out  of  the  tympanic  membrane  by  the  compressed 
air,  which  at  that  moment  enters  the  Eustachian  tube. 


THE    SENSES.  57'.* 

Similarly  the  tympanic  membrane  maybe  pressed  in  by  rarefying  the 
air  in  the  tympanum.  This  can  be  readily  accomplished  by  closing  the 
mouth  and  nose,  and  making  an  inspirator}'  effort  and  at  the  same  time 
swallowing  (Valsalva).  In  both  cases  the  sense  of  hearing  is  temporarily 
dulled;  proving  that  equality  of  pressure  on  both  sides  of  the  tympanic 
membrane  is  necessary  for  its  full  efficiency. 

Functions  of  Eustachian  Tube. — The  principal  office  of  the  Eus- 
tachian tube,  in  Miiller's  opinion,  has  relation  to  the  prevention  of  these 
effects  of  increased  tension  of  the  membrana  tympani.  Its  existence  and 
openness  will  provide  for  the  maintenance  of  the  equilibrium  between 
the  air  within  the  tympanum  and  the  external  air,  so  as  to  prevent  the 
inordinate  tension  of  the  membrana  tympani  which  would  be  produced 
by  too  great  or  too  little  pressure  on  either  side.  While  discharging  this 
office,  however,  it  will  serve  to  render  sounds  clearer,  as  (ELenle  suggests) 
the  apertures  in  violins  do;  to  supply  the  tympanum  with  air;  and  to  be 
an  outlet  for  mucus.  If  the  Eustachian  tube  were  permanently  open, 
the  sound  of  one's  own  voice  would  probably  be  greatly  intensified,  a 
condition  which  would  of  course  interfere  with  the  perception  of  other 
sounds.  At  any  rate,  it  is  certain  that  sonorous  vibrations  can  be  propa- 
gated up  the  Eustachian  tube  to  the  tympanum  by  means  of  a  tube  in- 
serted into  the  pharyngeal  orifice  of  the  Eustachian  tube. 

Action  of  the  Tensor  Tympani. — The  influence  of  the  tensor  tym- 
pani muscle  in  modifying  hearing  may  also  be  probably  explained  in  con- 
nection with  the  regulation  of  the  tension  of  the  membrana  tympani. 
If,  through  reflex  nervous  action,  it  can  be  excited  to  contraction  by  a 
very  loud  sound,  just  as  the  iris  and  orbicularis  palpebrarum  muscle  are 
by  a  very  intense  light,  then  it  is  manifest  that  a  very  intense  sound 
would,  through  the  action  of  this  muscle,  induce  a  deafening  or  muffling 
of  the  ears.  In  favor  of  this  supposition  we  have  the  fact  that  a  loud 
sound  excites,  by  reflection,  nervous  action,  winking  of  the  eyelids,  and, 
in  persons  of  irritable  nervous  system,  a  sudden  contraction  of  many 
muscles. 

Action  of  the  Stapedius. — The  influence  of  the  stapedius  muscle  in 
hearing  is  unknown.  It  acts  upon  the  stapes  in  such  a  manner  as  to 
make  it  rest  obliquely  in  the  fenestra  ovalis,  depressing  that  side  of  it  on 
which  it  acts,  and  elevating  the  other  side  to  the  same  extent.  It  pre- 
vents too  great  a  movement  of  the  bone. 

Functions  of  the  Fluid  of  the  Labyrinth. — The  fluid  of  the  laby- 
rinth is  the  most  general  and  constant  of  the  acoustic  provisions  of  the 
labyrinth.  In  all  forms  of  organs  of  hearing,  the  sonorous  vibrations 
affect  the  auditory  nerve  through  the  medium  of  liquid — the  most  con- 
venient medium,  on  many  accounts,  for  such  a  purpose. 

The  crystalline  pulverulent  masses  (otoliths)  in  the  labyrinth  would 
reinforce  the  sonorous  vibrations  by  their  resonance,  even  if  they  did  not 


580  HANDBOOK    OF    PHYSIOLOGY. 

actually  touch  the  membranes  upon  which  the  nerves  are  expanded;  butr 
inasmuch  as  these  bodies  lie  in  contact  with  the  membranous  parts 
of  the  labyrinth,  and  the  vestibular  nerve-fibres  are  imbedded  in  them, 
they  communicate  to  these  membranes  and  the  nerves,  vibratory  im- 
pulses of  greater  intensity  than  the  fluid  of  the  labyrinth  can  impart. 
This-  appears  to  be  their  office.  Sonorous  undulations  in  water  are  not 
perceived  by  the  hand  itself  immersed  in  the  water,  but  are  felt  distinctly 
through  the  medium  of  a  rod  held  in  the  hand.  The  fine  hair-like  pro- 
longations from  the  epithelial  cells  of  the  ampullse  have,  probably,  the 
same  function. 

Functions  of  the  Semicircular  canals. — Besides  the  function  of 
collecting  in  their  fluid  contents  sonorous  undulations  from  the  bones  of 
the  cranium,  the  semicircular  canals  appear  to  have  another  function  less 
directly  connected  with  the  sense  of  hearing.  Experiments  show  that 
when  the  horizontal  canal  is  divided  in  a  pigeon  a  constant  movement  of 
the  head  from  side  to  side  occurs,  and  similarly,  when  one  of  the  vertical 
canals  is  operated  upon,  up  and  down  movements  of  the  head  are  ob- 
served. These  movements  are  associated,  also,  with  loss  of  co-ordination 
as  after  the  operation  the  bird  is  unable  to  fly  in  an  orderly  manner,  but 
flutters  and  falls  when  thrown  into  the  air,  and,  moreover,  is  able  to  feed 
with  difficulty.  Hearing  remains  unimpaired.  It  has  been  suggested, 
therefore,  that  as  loss  of  co-ordination  results  from  section  of  these 
canals,  and  as  co-ordinate  muscular  movements  appear  to  depend  to  a 
considerable  extent  for  their  due  performance  upon  a  correct  notion  of 
our  equilibrium,  that  the  semicircular  canals  are  connected  in  some  way 
with  this  sense,  possibly  by  the  constant  alterations  of  the  pressure  of 
the  fluid  within  them:  the  change  in  the  pressure  of  the  fluid  in  each 
canal  which  takes  place  on  any  movement  of  the  head,  producing  sensa- 
tions which  aid  in  forming  an  exact  judgment  of  the  alteration  of  posi- 
tion which  has  occurred. 

Functions  of  the  Cochlea. — The  cochlea  seems  to  be  constructed 
for  the  spreading  out  of  the  nerve-fibres  over  a  wide  extent  of  surface* 
upon  a  solid  lamina  which  communicates  with  the  solid  walls  of  the 
labyrinth  and  cranium,  at  the  same  time  that  it  is  in  contact  with  the 
fluid  of  the  labyrinth,  and  which,  besides  exposing  the  nerve-fibres  to  the 
influence  of  sonorous  undulations,  by  two  media,  is  itself  insulated  by 
fluid  on  either  side. 

The  connection  of  the  lamina  spiralis  with  the  solid  walls  of  the 
labyrinth,  adapts  the  cochlea  for  the  perception  of  sonorous  undulations 
propagated  by  the  solid  parts  of  the  head  and  the  walls  of  the  labyrinth. 
The  membranous  labyrinth  of  the  vestibule  and  semicircular  canals  is 
suspended  free  in  the  perilymph,  and  is  destined  more  particularly  for 
the  perception  of  sounds  through  the  medium  of  that  fluid,  whether  the 
sonorous  undulations  be  imparted  to  the  fluid  through  the  fenestrae,  or 


THE   SENSES.  581 

"by  the  intervention  of  the  cranial  bones,  as  when  sounding  bodies  are 
brought  into  communication  with  the  head  or  teeth.  The  spiral  lamina 
on  which  the  nervous  fibres  are  expanded  in  the  cochlea,  is,  on  the  con- 
trary, continuous  with  the  solid  walls  of  the  labyrinth,  and  receives 
directly  from  them  the  impulses  which  they  transmit.  This  is  an  im- 
portant advantage;  for  the  impulses  imparted  by  solid  bodies  have, 
cmteris  paribus,  a  greater  absolute  intensity  than  those  communicated 
by  water.  And,  even  when  a  sound  is  excited  in  the  water,  the  sonorous 
undulations  are  more  intense  in  the  water  near  the  surface  of  the  vessel 
containing  it,  than  in  other  parts  of  the  water  equally  distant  from  the 
point  of  origin  of  the  sound;  thus  we  may  conclude  that,  catteris pari- 
bus, the  sonorous  undulations  of  solid  bodies  act  with  greater  intensity 
than  those  of  water.  Hence,  we  perceive  at  once  an  important  use  of 
the  cochlea. 

This  is  not,  however,  the  sole  office  of  the  cochlea;  the  spiral  lamina 
as  well  as  the  membranous  labyrinth,  receives  sonorous  impulses  through 
the  medium  of  the  fluid  of  the  labyrinth  from  the  cavity  of  the  vestibule, 
and  from  the  fenestra  rotunda.  The  lamina  spiralis  is,  indeed,  much 
better  calculated  to  render  the  action  of  these  undulations  upon  the  audi- 
tory nerve  efficient,  than  the  membranous  labyrinth  is;  for  as  a  solid 
body  insulated  by  a  different  medium,  it  is  capable  of  resonance. 

The  rods  of  Corti  are  probably  arranged  so  that  each  is  set  to  vibrate  in 
unison  with  a  particular  tone,  and  thus  strike  a  particular  note,  the  sen- 
sation of  which  is  carried  to  the  brain  by  those  filaments  of  the  auditory 
nerve  with  which  the  little  vibrating  rod  is  connected.  The  distinctive 
function,  therefore,  of  these  minute  bodies  is,  probably,  to  render  sensi- 
ble to  the  brain  the  various  musical  notes  and  tones,  one  of  them  answer- 
ing to  one  tone,  and  one  to  another;  while  perhaps  the  other  parts  of  the 
organ  of  hearing  discriminate  between  the  intensities  of  different  sounds, 
rather  than  their  qualities. 

"  In  the  cochlea  we  have  to  do  with  a  series  of  apparatus  adapted  for 
performing  sympathetic  vibrations  with  wonderful  exactness.  We  have 
here  before  us  a  musical  instrument  which  is  designed,  not  to  create  musi- 
cal sounds,  but  to  render  them  perceptible,  and  which  is  similar  in  con- 
struction to  artificial  musical  instruments,  but  which  far  surpasses  them 
in  the  delicacy  as  well  as  the  simplicity  of  its  execution.  For,  while  in  a 
piano  every  string  must  have  a  separate  hammer  by  means  of  which  it  is 
sounded,  the  ear  possesses  a  single  hammer  of  an  ingenious  form  in  its 
ear-bones,  which  can  make  every  string  of  the  organ  of  Corti  sound  sep- 
arately."    (Bernstein.) 

About  3000  rods  of  Corti  are  present  in  the  human  ear;  this  would 
give  about  400  to  each  of  the  seven  octaves  which  are  within  the  compass 
of  the  ear.  Thus  about  32  would  go  to  each  semi-tone.  Weber  assert- 
that  accomplished  musicians  can  appreciate  differences  in  pitch  as  small 
as  -$\  of  a  tone.  Thus,  on  the  theory  above  advanced,  the  delicacy  of 
discrimination  would,  in  this  case,  appear  to  have  reached  its  limits. 


582  HANDBOOK    OF    PHYSIOLOGY. 

Sensibility  of  the  Auditory  Nerve. — Auy  elastic  body,  e.  g.,  air,  a, 
membrane,  or  a  string  performing  a  certain  number  of  regular  vibrations 
in  the  second,  gives  rise  to  what  is  termed  a  musical  sound  or  tone.  We 
must,  however,  distinguish  between  a  musical  sound  and  a  mere  noise; 
the  latter  being  due  to  irregular  vibrations. 

Sounds. 

Qualities  of  Musical  Sounds. — Musical  sounds  are  distinguished  from 
each  other  by  three  qualities.  1.  Strength  or  intensity,  which  is  due  to 
the  amplitude  or  length  of  the  vibrations.  2.  Pitch,  which  depends 
upon  the  number  of  vibrations  in  a  second.  3.  Quality,  Color,  or  Timbre. 
It  is  by  this  property  that  we  distinguish  the  same  note  sounded  on  two 
instruments,  e.  g.,  a  piano  and  a  flute.  It  has  been  proved  by  Helm- 
holtz  to  depend  on  the  number  of  secondary  notes,  termed  harmonics, 
which  are  present  with  the  predominating  or  fundamental  tone. 

It  would  appear  that  two  impulses,  which  are  equivalent  to  four  sin- 
gle or  half  vibrations,  are  sufficient  to  produce  a  definite  note,  audible  as 
such  through  the  auditory  nerve.  The  note  produced  by  the  shocks  of 
the  teeth  of  a  revolving  wheel,  at  regular  intervals  upon  a  solid  body,  is 
still  heard  when  the  teeth  of  the  wheel  are  removed  in  succession,  until 
two  only  are  left;  the  sound  produced  by  the  impulse  of  these  two  teeth 
has  still  the  same  definite  value  in  the  scale  of  music. 

The  maximum  and  minimum  of  the  intervals  of  successive  impulses 
still  appreciable  through  the  auditory  nerve  as  determinate  sounds,  have 
been  determined  by  M.  Savart.  If  their  intensity  is  sufficiently  great, 
sounds  are  still  audible  which  result  from  the  succession  of  48,000  half 
vibrations,  or  24,000  impulses  in  a  second;  and  this,  probably,  is  not  the 
extreme  limit  in  acuteness  of  sounds  perceptible  by  the  ear.  For  the 
opposite  extreme,  he  has  succeeded  in  rendering  sounds  audible  which 
were  produced  by  only  fourteen  or  eighteen  half  vibrations,  or  seven  or 
eight  impulses  in  a  second;  and  sounds  still  deeper  might  probably  be 
heard,  if  the  individual  impulses  could  be  sufficiently  prolonged. 

By  removing  one  or  several  teeth  from  the  toothed  wheel  the  fact  has 
been  demonstrated  that  in  the  case  of  the  auditory  nerve,  as  in  that  of 
the  optic  nerve,  the  sensation  continues  longer  than  the  impression 
which  causes  it;  for  a  removal  of  a  tooth  from  the  wheel  produced  no 
interruption  of  the  sound.  The  gradual  cessation  of  the  sensation  of 
sound  renders  it  difficult,  however,  to  determine  its  exact  duration  be- 
yond that  of  the  impression  of  the  sonorous  impulses. 

Direction. — The  power  of  perceiving  the  direction  of  sounds  is  not  a 
faculty  of  the  sense  of  hearing  itself,  but  is  an  act  bf  the  mind  judging 
on  experience  previously  acquired.  From  the  modifications  which  the 
sensation  of  sound  undergoes  according  to  the  direction  in  which  the 
sound  reaches  us,  the  mind  infers  the  position  of  the  sounding  body. 
The  only  true  guide  for  this  inference  is  the  more  intense  action  of  the 


THE    SENSES. 


583 


sound  upon  one  than  upon  the  other  ear.  But  even  here  there  is  room 
for  much  deception,  by  the  influence  of  reflexion  or  resonance,  and  by 
the  propagation  of  sound  from  a  distance,  without  loss  of  intensity, 
through  curved  conducting  tubes  filled  with  air.  By  means  of  such 
tubes,  or  of  solid  conductors,  which  convey  the  sonorous  vibrations  from 
their  source  to  a  distant  resonant  body,  sounds  may  be  made  to  appear 
to  originate  in  a  new  situation.  The  direction  of  sound  may  also  be 
judged  of  by  means  of  one  ear  only;  the  position  of  the  ear  and  head  be- 
ing varied,  so  that  the  sonorous  undulations  at  one  moment  fall  upon  the 
ear  in  a  perpendicular  direction,  at  another  moment  obliquely.  But 
when  neither  of  these  circumstances  can  guide  us  in  distinguishing  the 
directiou  of  sound,  as  when  it  falls  equally  upon  both  ears,  its  source 
being,  for  example,  either  directly  in  front  or  behind  us,  it  becomes  im- 
possible to  determine  whence  the  sound  comes. 

Distance. — The  distance  of  the  source  of  sounds  is  not  recognized  by 
the  sense  itself,  but  is  inferred  from  their  intensity.  The  sound  itself  is 
always  seated  but  in  one  place,  namely,  in  our  ear;  but  it  is  interpreted 
as  coming  from  an  exterior  soniferous  body.  When  the  intensity  of  the 
voice  is  modified  in  imitation  of  the  effect  of  distance,  it  excites  the  idea 
of  its  originating  at  a  distance.  Ventriloquists  take  advantage  of  the 
difficulty  with  which  the  direction  of  sound  is  recognized,  and  also  the 
influence  of  the  imagination  over  our  judgment,  when  they  direct  their 
voice  in  a  certain  direction,  and  at  the  same  time  pretend,  themselves,  to 
hear  the  sounds  as  coming  from  thence. 

The  effect  of  the  action  of  sonorous  undulations  upon  the  nerve  of 
hearing,  endures  somewhat  longer  than  the  period  during  which  the  un- 
dulations are  passing  through  the  ear.  If,  however,  the  impressions  of 
the  same  sound  be  very  long  continued,  or  constantly  repeated  for  a  long 
time,  then  the  sensation  produced  may  continue  for  a  very  long  time, 
more  than  twelve  or  twenty-four  hours  even,  after  the  original  cause  of 
the  sound  has  ceased. 

Binaural  Sensations. — Corresponding  to  the  double  vision  of  the 
same  object  with  the  two  eyes,  is  the  double  hearing  with  the  two  ears; 
and  analogous  to  the  double  vision  with  one  eye,  dependent  on  unequal 
refraction,  is  the  double  hearing  of  a  single  sound  with  one  ear,  owing  to 
the  sound  coming  to  the  ear  through  media  of  unequal  conducting  power. 
The  first  kind  of  double  hearing  is  very  rare;  instances  of  it,  however, 
have  been  recorded.  The  second  kind,  which  depends  on  the  unequal 
conducting  power  of  two  media  through  which  the  same  sound  is  trans- 
mitted to  the  ear,  may  easily  be  experienced.  If  a  small  bell  be  sounded 
in  water,  while  the  ears  are  closed  by  plugs,  and  a  solid  conductor  be 
interposed  between  the  water  and  the  ear,  two  sounds  will  be  hoard  dif- 
fering in  intensity  and  tone;  one  being  conveyed  to  the  car  through  the 
medium  of  the  atmosphere,  the  other  through  the  couducting-rod. 


584  HANDBOOK   OF    PHYSIOLOGY. 

Subjective  Sensations. — Subjective  sounds  are  the  result  of  a  state  of 
irritation  or  excitement  of  the  auditory  nerve  produced  by  other  causes 
than  sonorous  impulses.  A  state  of  excitement  of  this  nerve,  however 
induced,  gives  rise  to  the  sensation  of  sound.  Hence  the  ringing  and 
buzzing  in  the  ears  heard  by  persons  of  irritable  and  exhausted  nervous 
system,  and  by  patients  with  cerebral  disease,  or  disease  of  the  auditory 
nerve  istelf ;  hence  also  the  noise  in  the  ears  heard  for  some  time  after  a 
long  journey  in  a  rattling  noisy  vehicle.  Ritter  found  that  electricity 
also  excites  a  sound  in  the  ears.  From  the  above  truly  subjective  sound 
we  must  distinguish  those  dependent,  not  on  a  state  of  the  auditory  nerve 
itself  merely,  but  on  sonorous  vibrations  excited  in  the  auditory  appa- 
ratus. Such  are  the  buzzing  sounds  attendant  on  vascular  congestion  of 
the  head  and  ear,  or  on  aneurismal  dilatation  of  the  vessels.  Frequently 
even  the  simple  pulsatory  circulation  of  the  blood  in  the  ear  is  heard. 
To  the  sounds  of  this  class  belong  also  the  buzz  or  hum,  heard  during 
the  contraction  of  the  palatine  muscles  in  the  act  of  yawning,  during 
the  forcing  of  air  into  the  tympanum  so  as  to  make  tense  the  membrana 
tympani,  and  in  the  act  of  blowing  the  nose,  as  well  as  during  the  for- 
cible depression  of  the  lower  jaw. 

Irritation  or  excitement  of  the  auditory  nerve  is  capable  of  giving 
rise  to  movements  in  the  body,  and  to  sensations  in  other  organs  of 
sense.  In  both  cases  it  is  probable  that  the  laws  of  reflex  action,  through 
the  medium  of  the  brain,  come  into  play.  An  intense  and  sudden  noise 
excites,  in  every  person,  closure  of  the  eyelids,  and,  in  nervous  individ- 
uals, a  start  of  the  whole  body  or  an  unpleasant  sensation,  like  that  pro- 
duced by  an  electric  shock,  throughout  the  body,  and  sometimes  a 
particular  feeling  in  the  external  ear.  Various  sounds  cause  in  many 
people  a  disagreeable  feeling  in  the  teeth,  or  a  sensation  of  cold  tickling 
through  the  body,  and,  in  some  people,  intense  sounds  are  said  to  make 
the  saliva  collect. 

V.    Sight. 

Anatomy  of  the  Optical  Apparatus. — The  eyelids  consist  of  two 
movable  folds  of  skin,  each  of  which  is  kept  in  shape  by  a  thin  plate  of 
yellow  elastic  tissue.  Along  their  free  edges  are  inserted  a  number  of 
curved  hairs  (eyelashes),  which,  when  the  lids  are  half  closed,  serve  to 
protect  the  eye  from  dust  and  other  foreign  bodies:  their  tactile  sensibil- 
ity is  also  very  delicate. 

On  the  inner  surface  of  the  elastic  tissue  are  disposed  a  number  of 
small  racemose  glands  (Meibomian),  whose  ducts  open  near  the  free  edge 
of  the  lid. 

The  orbital  surface  of  each  lid  is  lined  by  a  delicate,  highly  sensitive 
mucous  membrane  (conjunctiva),  which  is  continuous  with  the  skin  at 
the  free  edge  of  each  lid,  and  after  lining  the  inner  surface  of  the  eyelid 
is  reflected  on  to  the  eyeball,  being  somewhat  loosely  adherent  to  the 
sclerotic  coat.  The  epithelial  layer  is  continued  over  the  cornea  at  its 
anterior  epithelium.     At  the  inner  edge  of  the  eye  the  conjunctiva  be- 


THE    SENSES. 


585 


comes  continuous  with  the  mucous  lining  of  the  lachrymal  sac  and  duct, 
which  again  is  continuous  with  the  mucous  membrane  of  the  inferior 
meatus  of  the  nose. 

The  lachrymal  gland  is  lodged  in  the  upper  and  outer  angle  of  the 
orbit.  Its  secretion,  which  issues  from  several  ducts  on  the  inner  sur- 
face of  the  upper  lid,  under  ordinary  circumstances  just  suffices  to  keep 
the  conjunctiva  moist.  It  passes  out  through  two  small  openings  (puncta 
lachrymalia)  near  the  inner  angle  of  the  eye,  one  in  each  lid,  into  the 
lachrymal  sac,  and  thence  along  the  nasal  duct  into  the  inferior  meatus 
of  the  nose.  The  excessive  secretion  poured  out  under  the  influence  of 
any  irritating  vapor  or  painful  emotion  overflows  the  lower  lid  in  the 
form  of  tears. 

The  eyelids  are  closed  by  the  contraction  of  a  sphincter  muscle 
{orbicularis),  supplied  by  the  Facial  nerve;  the  upper  lid  is  raised  by  the 
Levator  palpebrce  super ioris,  which  is  supplied  by  the  Third  nerve. 

The   Eyeball. 

The  eyeball  or  the  organ  of  vision  (Fig.  390)  consists  of  a  variety  of 
structures  which  may  be  thus  enumerated:  — 

The  sclerotic,  or  outermost  coat,  envelops  about  five-sixths  of  the 
eyeball:  continuous  with  it,  in  front,  and  occupying  the  remaining  sixth, 
is  the  cornea.  Immediately  within  the  sclerotic  is  the  choroid  coat,  and 
within  the  choroid  is  the  retina.  The  interior  of  the  eyeball  is  well-nigh 
filled  by  the  aqueous  and  vitreous  humors  and  the  crystalline  lens;  but, 


Ciliary  muscle- 
Ciliary  process — 
Canal  of  Petit- 
Cornea— 
Anterior  chamber- 


Lens— 
Iris- 
Ciliary  process- 
Ciliary  muscle 


Fig.  390 


also,  there  is  suspended  in  the  interior  a  contractile  and  perforated  cur- 
tain— the  iris,  for  regulating  the  admission  of  light,  and  behind  the 
junction  of  the  sclerotic  and  cornea  is  the  ciliary  muscle,  the  function 
of  which  is  to  adapt  the  eye  for  seeing  objects  at  various  distances. 


5S6 


HANDBOOK    OF    PHYSIOLOGY. 


Structure  of  the  Sclerotic  Coat.— The  sclerotic  coat  is  composed  of 
connective  tissue,  arranged  in  variously  disposed  and  inter-communicat- 
ing layers.     It  is  strong,  tough,  and  opaque,  and  not  very  elastic. 

Structure  of  the  Cornea.— The  cornea  is  a  transparent  membrane 
which  forms  a  segment  of  a  smaller  sphere  than  the  rest  of  the  eyeball, 
and  is  let  in,  as  it  were,  into  the  sclerotic  with  which  it  is  continuous  all 
round.  It  is  coated  with  a  laminated  anterior  epithelium  {a,  Fig.  393), 
consisting  of  seven  or  eight  layers  of  cells,  of  which  the  superficial  ones 
are  flattened  and  scaly,  and  the  deeper  ones  more  or  less  columnar.  Im- 
mediately beneath  this  is  the  anterior  elastic  lamina  (Bowman). 


Fig.  392. 

Fig.  391.— Vertical  section  of  rabbit's  cornea,  stained  with  gold  chloride,  e,  Laminated  anterior 
epithelium.  Immediately  beneath  this  is  the  anterior  elastic  lamina  of  Bowman,  n,  Nerves  forming 
a  delicate  sub-epithelial  plexus,  and  sending  up  fine  twigs  between  the  epithelial  cells  to  end  in  a 
second  plexus  on  the  free  surface ;  d,  Descemet's  membrane,  consisting  of  a  fine  elastic  layer,  and 
a  single  layer  of  epithelial  cells;  the  substance  of  the  cornea,  /,  is  seen  to  be  fibrillated,  and  con- 
tains many  layers  of  branched  corpuscles,  arranged  parallel  to  the  free  surface,  and  here  seen  edge- 
wise.   (Schofleldj 

Fig.  392.— Section  through  the  choroid  coat  of  the  human  eye.  1,  elastic  membrane,  structure- 
less or  finely  fibrillated;  a,  chorio-capillaris or  tunica  Ruyschiana;  3,  Proper  substance  of  the  cho- 
roid with  large  vessels  cut  through;  4,  suprachoroidea ;  5,  sclerotic.    (Schwalbe.) 

The  cornea  tissue  proper  as  well  as  its  epithelium  is,  in  the  adult, 
completely  destitute  of  blood-vessels;  it  consists  of  an  intercellular 
ground-substance  of  rather  obscurely  fibrillated  flattened  bundles  of  con- 
nective tissue,  arranged  parallel  to  the  free  surface,  and  forming  the 
boundaries  of  branched  anastomosing  spaces  in  which  the  cornea-cor- 
puscles lie.     These  branched  cornea-corpuscles  have  been  seen  to  creep 


THE    SENSES. 


58T 


by  amoeboid  movement  from  one  branched  space  into  another.  At  its 
posterior  surface  the  cornea  is  limited  by  the  posterior  elastic  lamina,  or 
membrane  of  Descemet,  the  inner  layer  of  which  consists  of  a  single 
stratum  of  epithelial  cells  (Fig.  391,  d). 

Nerves. — The  nerves  of  the  cornea  are  both  large  and  numerous:  they 
are  derived  from  the  ciliary  nerves.     They  traverse  the  substance  of  the 


Fig.  393.— Vertical  section  of  rabbit's  cornea,  a.  Anterior  epithelium,  showing  the  different 
shapes  of  the  cells  at  various  depths  from  the  free  surf  ace ;  b,  portion  of  the  substance  of  cornea. 
(Klein.) 

cornea,  in  which  some  of  them  terminate,  in  the  direction  of  its  anterior 
surface,  near  which  the  axis  cylinders  break  up  into  bundles  of  very  deli- 
cate beaded  fibrillar  (Fig.  391):  these  form  a  plexus  immediately  beneath 
the  epithelium,  from  which  delicate  fibrils  pass  up  between  the  cells  anas- 
tomosing with  horizontal  branches,  and  forming  a  deep  intra-epithelial 


Fio.  394.— Horizontal  preparation  of  cornea  of  frog;  showing  the  network  of  branched  cornea 
corpuscles.    The  ground  substance  is  completely  colorless,    x  400.    (Klein.) 

plexus,  from  which  fibres  ascend,  till  near  the  surface  they  form  a  super- 
ficial intra-epithelial  network. 

Structure  of  the  Choroid  Coat  (tunica  vasculosa). — This  coat  of  the 
eyeball  is  formed  by  a  very  rich  network  of  capillaries  (chorio-oapillaris) 
outside  which  again  are  connective-tissue  layers  of  stellate  pigmented 
cells,  suprachoroidea  (Fig.  392)  with  numerous  arteries  and  veins.     It  is 


588 


HANDBOOK    OF    PHYSIOLOGY. 


separated  from  the  retina  by  a  fine  elastic  membrane,  which  is  either 
structureless  or  finely  fibrillated. 

The  choroid  coat  ends  in  front  in  what  are  called  the  ciliary  pro- 
cesses (Fig.  399). 

Structure  of  the  Retina. — The  retina  (Fig.  396)  is  a  delicate  mem- 
brane, concave,  with  the  concavity  directed  forwards  and  ending  in 
front,  near  the  outer  part  of  the  ciliary  processes,  in  a  finely  notched 
edge — the  ora  serrata.  Semitransparent  when  fresh,  it  soon  becomes 
clouded  and  opaque,  with  a  pinkish  tint  from  the  blood  in  its  minute 
vesselsi  It  results  from  the  sudden  spreading  out  or  expansion  of  the 
optic  nerve,  of  whose  terminal  fibres,  apparently  deprived  of  their  exter- 
nal white  substance,  together  with  nerve  cells,  it  is  essentially  composed. 

Exactly  in  the  centre  of  the  retina,  and  at  a  point  thus  correspond- 
ing to  the  axis  of  the  eye  in  which  the  sense  of  vision  is  most  perfect,  is 
&  round  yellowish  elevated  spot,  about  ^  of  an  inch  in  diameter,  having 
a  minute  aperture  at  its  summit,  and  called  after  its  discoverer  the  yel- 


Fig.  395.— Surface  view  of  part  of  lamella  of  kitten's  cornea,  prepared  first  with  caustic  potash 
and  then  with  nitrate  of  silver.  (By  this  method  the  branched  cornea-corpuscles  with  their  granu- 
lar protoplasm  and  large  oval  nuclei  are  brought  out.)    x  450.    (Klein  and  Noble  Smith.) 

low  spot  of  Soemmering.  In  its  centre  is  a  minute  depression  called  fo- 
vea centralis.  About  TV  of  an  inch  to  the  inner  side  of  the  yellow  spot, 
and  consequently  of  the  axis  of  the  eye,  is  the  point  at  which  the  optic 
nerve  begins  to  spread  out  its  fibres  to  form  the  retina.  This  is  the  only 
point  of  the  surface  of  the  retina  from  which  the  power  of  vision  is  ab- 
sent. 

The  retina  consists  of  certain  nervous  elements  arranged  in  several 
layers,  and  supported  by  a  very  delicate  connective  tissue. 

From  the  nature  of  the  case  there  is  still  considerable  uncertainty  as 
to  the  character  (nervous  or  connective  tissue)  of  some  of  the  layers  of 
the  retina.  The  following  ten  layers,  from  within  outwards,  are  usually 
to  be  distinguished  in  a  vertical  section  (Figs.  396,  399). 

1.  Merribrana  limitans  interna :  a  delicate  membrane  in  contact  with 
the  vitreous  humor. 

2.  Fibres  of  optic  nerve.  This  layer  is  of  very  varying  thickness  in 
different  parts  of  the  retina:  it  consists  chiefly  of  non-medullated  fibres 


THE    SENSES. 


:,v. 


which  interlace,   and  some  of  which  are   continuous  with  processes  of 
large  nerve-cells  forming  the  next  layer. 

3.  Layer  of  ganglionic  corpuscles,  consisting  of  large  multipolar 
nerve-cells,  sometimes  forming  a  single  layer.  In  some  parts  of  the 
retina,  especially  near  the  macula  lutea.  this  layer  is  very  thick,  consist- 
ing of  several  distinct  strata  of  nerve-cells.  These  cells  lie  in  the  spaces 
of  a  connective-tissue  framework. 

4.  Molecular  layer.  This  presents  a  finely  granulated  appearance. 
It  consists   of   a    punctiform   connective 

tissue  traversed  by  numberless  very  fine 
fibrillar  processes  of  the  nerve-cells. 

5.  Internal  granular  layer.  This  con- 
sists chiefly  of  numerous  small  round  cells 
with  a  very  small  quantity  of  protoplasm 
surrounding  a  large  nucleus;  they  are 
generally  bipolar,  giving  off  one  process 
outwards  and  another  iuwards.  They 
greatly  resemble  the  ganglionic  corpuscles 
of  the  cerebellum.  Besides  these  there 
are  jarge  oval  nuclei  (e' ',  Fig.  396  A)  be- 
longing to  the  sustentacular  connective- 
tissue  fibres. 

6.  Intergranular  layer;  which  closely 
resembles  the  molecular  layer  but  is  much 
thinner.  It  consists  of  finely-dotted  con- 
nective tissue  with  nerve  fibrils. 

7.  External  granular  layer;  which  con- 
sists of  several  strata  of  small  cells  re- 
sembling those  of  the  internal  granular 
layer;  they  have  been  classed  as  rod  and 
cone  granules,  according  as  they  are  con- 
nected by  very  delicate  fibrils  with  the 
rods  and  cones  respectively.  They  are 
lodged  in  the  meshes  of  a  connective-tissue 
framework.  Both  the  internal  and  ex- 
ternal granular  layer  stain  very  rapidly  and 
deeply  with  hematoxylin,  while  the  rod 
and  cone  layer  remains  quite  unstained. 

8.  Membrana  limitans  externa;  a  deli- 
cate, well-defined  membrane,  clearly  marking  the  internal  limit  of  the 
rod  and  cone  layer. 

9.  Bod  and  cone  layer,  bacillar  layer,  or  membrane  of  Jacob,  consist- 
ing of  two  kinds  of  elements:  the  "rods,"  which  are  cylindrical  and  of 
uniform  diameter  throughout,  and  the  "  cones,"  whose  internal  portion 


Fig.  396.— Diagram  of  the  retina. 
A,  connective  tissue  portion;  B,  ner- 
vous portion  fthe  two  must  be  com- 
bined to  form  the  complete  retina);  a 
a,  membrana  limitans  externa;  6, 
rods;  c,  cones:  b\  rod-granuale  :  c*, 
cone-granule;  both  belonging  to  the 
external  granule  layer;  e,  Muller's 
sustentacular  fibres.  *  with  their  nu- 
clei e'\  d,  intergranular  layer;  /.  in- 
ternal granule  layer;  g,  molecular 
layer,  connective-tissue  portion:  </', 
molecular  layer,  nerve-fibril  portion; 
h.  ganglion  cells;  W.  their  axis-cylin- 
der process;  j,  nerve-fibre  layer.  OIux 
Schultze.) 


590 


handbook;  of  physiology, 


is  distinctly  conical,  and  surmounted  externally  by  a  thin  rod-like  body. 
According  to  the  researches  of  Max  Schultze,  the  rods  show  traces  of 
longitudinal  fibrillation,  and,  moreover,  have  a  great  tendency  to  break 
up  into  a  number  of  transverse  discs  like  a  pile  of  coins. 

In  the  rod  and  cone  layer  of  birds,  the  cones  usually  predominate 
largely  in  number,  whereas  in  man  the  rods  are  by  far  the  more  numer- 
ous. In  nocturnal  birds,  however,  such  as  the  owl,  only  rods  are  present, 
and  the  same  appears  to  be  the  case  in  many  nocturnal  and  burrowing 
mammalia,  e.  g.,  bat,  hedge-hog,  mouse,  and  mole. 

10.  Pigment  cell  layer,  which  was  formerly  considered  part  of  the 
choroid.  It  consists  of  hexagonal  and  unbranched  cells  with  a  light 
nucleus. 

In  the  centre  of  the  yellow  spot  (macula  lutea)  all  the  layers  of  the 
retina  become  greatly  thinned  out  and  almost  disappear,  except  the  rod 


Fig. 


Fig.  397.  Fig. 

397.—  Ciliary  processes,  as  seen  from  behind.    8,  posterior  surface  of  the  iris,  with  the 


sphincter  muscle  of  the  pupil;  2,  anterior  part  of  the  choroid  coat;  3,  one  of  the  ciliary  processes,  of 
which  about  seventy  are  represented.    %. 

Fig.  398.— The  posterior  half  of  the  retina  of  the  left  eye.  viewed  from  before;  *,  the  cut  edge  of 
the  sclerotic  coat;  ch,  the  choroid;  r,  the  retina;  in  the  interior  at  the  middle,  the  macula  lutea  with 
the  depression  of  the  fovea  centralis  is  represented  by  a  slight  oval  shade;  towards  the  left  side  the 
light  spot  indicates  the  eolliculus  or  eminence  at  the  entrance  of  the  optic  nerve,  from  the  centre  of 
which  the  arteria  centralis  is  seen  spreading  its  branches  into  the  retina,  leaving  the  part  occupied 
by  the  macula  comparatively  free.    (After  Henle.) 

and  cone  layer,  which  considerably  increases  in  thickness,  and  comes  to 
consist  almost  entirely  of  long  slender  cones,  the  rods  being  very  few  in 
number,  or  entirely  absent.  There  are  capillaries  here,  but  none  of  the 
larger  branches  of  the  retinal  arteries. 

"With  regard  to  the  connection  of  the  various  layers  there  is  still  some 
uncertainty.  Fig.  396  represents  the  view  of  Max  Schultze.  Accord- 
ing to  this  there  are  certain  sustentacular  fibres  of  connective  tissue 
(radiating  fibres  of  Miiller)  which  spring  from  the  memorana  limitans 
interna  almost  vertically,  and  traverse  the  retina  to  the  limitans  ex- 
terna, whence  very  delicate  connective-tissue  processes  pass  up  between 
the  rods  and  cones.     The  framework  which  they  form  is  represented  in 


THE    SENSE 


591 


Fig.  396,  A.  The  nervous  elements  of  the  retina  are  represented  in  Fig. 
396,  B,  and  consist  of  delicate  fibres  passing  up  from  the  nerve-fibre 
layer  to  the  rods  and  cones,  and  connected  with  the  ganglionic  corpus- 
cles and  granules  of  the  internal  and  external  layer. 

Blood-vessels  of  the  Eye-ball. — The  eye  is  very  richly  supplied 
with  blood-vessels.  In  addition  to  the  conjunctival  vessels  which  are 
derived  from  the  palpebral  and  lachrymal  arteries,  there  are  at  least  two 
other  distinct  sets  of  vessels  supplying  the  tunics  of  the  eyeball.  (1) 
The  vessels  of  the  sclerotic,  choroid,  and  iris,  and  (2)  The  vessels  of  the 
retina. 

(1)  These  are  the  short  and  long  posterior  ciliary  arteries  which  pierce 
the  sclerotic  in  the  posterior  half  of  the  eyeball,  and  the  anterior  ciliary 
which  enter  near  the  insertions  of  the  recti.  These  vessels  anastomose 
and  form  a  very  rich  choroidal  plexus;  they  also  supply  the  iris  and 


k        |  3         m 


Fig.  399.— Section  through  the  eye  carried  through  the  ciliary  processes.  1,  Cornea;  2,  mem- 
brane of  Descemet;  3.  sclerotic;  3',  corneo-scleral  junction;  4,  canal  of  Schlemm;  5,  vein;  6.  nucle- 
ated network  on  inner  wall  of  canal  of  Schlemm;  7,  lig.  pectinatum  iridis,  abc;  8,  iris  stroma;  9, 
pigment  of  iris;  10,  ciliary  processes;  11,  ciliary  muscle;  12,  choroid  tissue;  13,  meridional  and  14. 
radiating  fibres  of  ciliary  muscle;.  15,  ring-muscle  of  Muller;  16,  circular  or  angular  bundles  of  cili- 
ary muscle.    (Schwaibe.) 

ciliary  processes,  forming  a  very  highly  vascular  circle  round  the  outer 
margin  of  the  iris  and  adjoining  portion  of  the  sclerotic. 

The  distinctness  of  these  vessels  from  those  of  the  conjunctiva  is  well 
seen  in  the  difference  between  the  bright  red  of  blood-shot  eyes  (con- 
junctival congestion1),  and  the  pink  zone  surrounding  the  cornea  which 
indicates  deep-seated  ciliary  congestion. 

(2)  The  retinal  vessels  are  derived  from  the  arteria  centralis  retinir, 
which  enters  the  eyeball  along  the  centre  of  the  optic  nerve.  They 
ramify  all  over  the  retina,  chiefly  in  its  inner  layers.  They  can  be  seen 
by  direct  ophthalmoscopic  examination. 

The  Crystalline  Lens.  Structure. — The  lens  is  made  up  of  a  series 
of  concentric  laminae  (Fig.  403),  which  when  it  has  been  hardened,  can 
be  peeled  off  like  the  leaves  of  an  onion.  The  laminae  consist  of  long  rib- 
bon-shaped fibres,  which  m  the  course  of  development  are  derived  from 
cells.     The  fibres,  therefore,  when  young  contain  oval  nuclei,  but  these 


592 


HANDBOOK    OF    PHYSIOLOGY. 


disappear  in  the  fully  developed  lens  except  at  the  outside.  The  super- 
ficial fibres  are  softer.  The  fibres  are  really  six-sided  prisms  when  seen 
in  section,  and  fit  exactly  together  with  little  connecting  material.  The 
capsule  is  a  homogeneous  transparent  elastic  membrane.     The  hardest 


Fig.  400. — A.  Section  of  the  retina,  choroid,  and  part  of  the  sclerotic,  moderately  magnified,  a, 
membrana  limitans interna:  b,  nerve-fibre  layer  traversed  by  M  tiller's  sustentacular  fibres  (of  the 
connective  tissue  system) ;  c,  ganglion  cell  layer;  d,  molecular  layer;  e,  internal  granular  layer;  /, 
intergranular  layer;  gr,  external  granular  layer;  h,  membrana  limitans  externa,  running  along  the 
lower  part  of  i,  the  layer  of  rods  and  cones;  fc,  pigment  cell  layer  formerly  described  as  part  of  the 
choroid;  I,  m,  internal  and  external  vascular  portions  of  the  choroid,  the  first  containing  capillaries, 
the  second  larger  blood-vessels,  cut  in  tranverse  sections;  n,  sclerotic.    (W.  Pye.) 


portion  of  the  lens  is  that  which  is  most  internal, 
called  nucleus  of  the  lens  (Fig.  403,  1). 


It  forms  the  so- 


Optical  Apparatus. 

The  eye  may  be  compared  to  the  camera  used  by  photographers,  and 
the  transparent  media  correspond  to  the  lens  which  is  screwed  into  the 
front  part.  In  the  photographic  camera  images  of  external  objects  are 
thrown  upon  a  ground-glass  screen  at  the  back  of  a  box,  the  interiox*  of 
which  is  painted  black.  In  the  eye  the  camera  proper  is  represented  by 
the  eye-ball  with  its  choroidal  pigment,  and  the  screen  by  the  retina. 
In  the  case  of  the  camera  the  screen  is  enabled  to  receive  clear  images 
of  objects  at  different  distances,  by  an  apparatus  for  focussing,  and  the 
convex  lens  too  can  be  screwed  in  and  out.  The  corresponding  contri- 
vance in  the  eye  will  be  described  under  the  head  of  Accommodation. 

The  essential  constituents  of  the  optical  apparatus  of  the  eye  may  be 
thus  enumerated:  (1)  A  nervous  structure  ('the  retina)  to  be  stimulated 


THE    SENSES. 


593 


by  light  and  to  transmit  by  means  of  the  optic  nerve,  of  which  it  is  the 
terminal  expansion,  the  impression  of  the  stimulation  to  the  brain,  in 
which  it  excites  the  sensation  of  vision;  (2)  An  apparatus  consisting  of 
certain  refracting  media,  cornea,  crystalline  lens,  aqueous  and  vitreous 


1ST- 


Fig.  401.— Section  through  the  macula  lutea  and  fovea  centralis  of  human  retina,    a,  fovea;  b, 
descent  of  the  macula  towards  fovea.    The  numbers  indicate  the  layers  of  the  retina.    (Kuhnt.) 

humor,  the  function  of  which  is  to  collect  together  into  one  point,  the 
different  divergent  rays  emitted  by  each  point  of  every  external  body  and 
of  giving  them  such  directions  that  they  are  exactly  focussed  upon  the 


Fig.  402.— Meridional  section  through  the  lens  of  a  rabbit.    1,  Lens  capsule;  2,  epithelium  of 
lens;  3,  transition  of  the  epithelium  into  the  fibres;  4.  lens  fibres.    (Bubuchin.) 

retina,  and  thus  produce  an  exact  image  of  the  object  from  Avhich  they 
proceed.  For  as  light  radiates  from  a  luminous  body  in  all  directions, 
when  the  media  offer  no  impediment  to  its  transmission,  aluminous  point 


Fig.  403. -Laminated  structure  of  the  crystalline  lens.    The  laminae  are  split  up  after  hardening 
in  alcohol.    1,  the  denser  central  part  or  nucleus;  2,  the  successive  external  layers.    4/1.    (Arnold.} 

will  necessarily  illuminate  all  parts  of  a  surface,  such  as  the  retina  opposed 
to  it,  and  not  merely  one  single  point.  A  retina,  therefore,  without  aut- 
optical apparatus  placed  in  front  of  it  to  separate  the  light  of  different 
objects,  would  not  allow  of  distinct  vision,  but  would  merely  transmit  such 
38 


594  HANDBOOK    OF    PHYSIOLOGY. 

a  general  impression  of  daylight  as  would  distinguish  it  from  the  night; 
(3)  A  contractile  diaphragm  (iris)  with  a  central  aperture  for  regulating 
the  quantity  of  light  admitted  into  the  eye;  and  (4)  an  arrangement  by 
which  the  chief  refracting  medium  shall  be  so  controlled  as  to  enable 
objects  to  be  seen  at  various  distances,  causing  convergence  of  the  rays 
of  light  that  fall  upon  and  traverse  it  (accommodation).  Of  the  re- 
fracting media  the  cornea  is  in  a  two-fold  manner  capable  of  refracting 
and  causing  convergence  of  the  rays  of  light  that  fall  upon  and  traverse 
it.  It  thus  affects  them  first,  by  its  density;  for  it  is  a  law  in  optics 
that  when  rays  of  light  pass  from  a  rarer  into  a  denser  medium,  if  they 
impinge  upon  the  surface  in  a  direction  removed  from  the  perpendicu- 
lar, they  are  bent  out  of  their  former  direction  towards  that  of  a  line 
perpendicular  to  the  surface  of  the  denser  medium,  and,  secondly,  by 
its  convexity;  since  rays  of  light  impinging  upon  a  convex  transpa- 
rent surface,  are  refracted  towards  the  centre,  those  being  most  refracted 
which  are  farthest  from  the  centre  of  the  convex  surface. 

Behind  the  cornea  is  a  space  containing  a  thin,  watery  fluid,  the 
aqueous  humor,  holding  in  solution  a  small  quantity  of  sodium  chloride 
and  extractive  matter.  The  space  containing  the  aqueous  humor  is  di- 
vided into  an  anterior  and  posterior  chamber  by  a  membranous  partition, 
the  iris,  to  be  presently  again  mentioned.  The  effect  produced  by  the 
aqueous  humor  on  the  rays  of  light  traversing  it,  is  not  yet  fully  ascer- 
tained. Its  chief  use,  probably,  is  to  assist  in  filling  the  eyeball,  so  as 
to  maintain  its  proper  convexity,  and  at  the  same  time  to  furnish  a 
medium  in  which  the  movements  of  the  iris  can  take  place. 

Behind  the  aqueous  humor  and  the  iris,  and  imbedded  in  the  anterior 
part  of  the  medium  next  to  be  described,  viz.,  the  vitreous  humor,  is 
seated  a  doubly-convex  body,  the  crystalline  lens,  which  is  the  most  im- 
portant refracting  structure  of  the  eye.  The  structure  of  the  lens  is 
very  complex.  It  consists  essentially  of  fibres  united  side  by  side  to  each 
other,  and  arranged  together  in  very  numerous  laminae,  which  are  so 
placed  upon  one  another,  that  when  hardened  in  spirit  the  lens  splits 
into  three  portions  in  the  form  of  sectors,  each  of  which  is  composed  of 
superimposed  concentric  laminae.  The  lens  increases  in  density  and, 
consequently,  in  power  of  refraction,  from  without  inwards;  the  central 
part,  usually*termed  the  nucleus,  being  the  most  dense. 

The  vitreous  humor  constitutes  nearly  four-fifths  of  the  whole  globe 
of  the  eye.  It  fills  up  the  space  between  the  retina  and  the  lens,  and  its 
soft  jelly-like  substance  consists  essentially  of  numerous  layers,  formed 
of  delicate,  simple  membrane,  the  spaces  between  which  are  filled  with 
a  watery,  pellucid  fluid.  Its  principal  use  appears  to  be  tha't  of  giving 
the  proper  distention  to  the  globe  of  the  eye,  and  of  keeping  the  surface 
of  the  retina  at  a  proper  distance  from  the  lens. 

Action  of  the  Iris. — The  iris  is  a  vertically-placed  membranous 


THE   SENSES;  595 

diaphragm,  provided  with  a  central  aperture,  the  pupil,  for  the  trans- 
mission of  light.  It  is  composed  of  plain  muscular  fibres  imbedded  in 
ordinary  fibro-cellular  or  connective  tissue.  The  muscular  fibres  have  a 
direction,  for  the  most  part,  radiating  from  the  circumference  towards 
the  pupil;  but  as  they  approach  the  pupillary  margiu,  they  assume  a  cir- 
cular direction,  and  at  the  very  edge  form  a  complete  ring.  By  the  con- 
traction of  the  radiating  fibres  (dilator  pupillas)  the  size  of  the  pupil  is 
enlarged:  by  the  contraction  of  the  circular  ones  (sphincter  pupilhe),  it 
is  diminished.  The  object  effected  by  the  movements  of  the  iris,  is  the 
regulation  of  the  quantity  of  light  transmitted  to  the  retina.  The  pos- 
terior surface  of  the  iris  is  coated  with  a  layer  of  dark  pigment,  so  that 
no  rays  of  light  can  pass  to  the  retina,  except  such  as  are  admitted 
through  the  aperture  of  the  pupil. 

This  iris  is  very  richly  supplied  with  nerves  and  blood-vessels.  Its 
circular  muscular  fibres  are  supplied  by  the  third  (by  the  short  ciliary 
branches  of  the  ophthalmic  ganglion),  and  its  radiating  fibres,  by  the 
sympathetic  and  fifth  cranial  nerve  (by  the  long  ciliary  branches  of  the 
nasal  nerve). 

Contraction  of  the  pupil  occurs  under  the  following  circumstances: 
(I)  On  exposure  of  the  eye  to  a  bright  light;  (2)  when  the  eye  is  focussed 
for  near  objects;  (3)  when  the  eyes  converge  to  look  at  a  near  object; 

(4)  on  the  local  application  of  eserine  (active  principle  of  Calabar  bean); 

(5)  on  the  administration  internally  of  opium,  aconite,  and  in  the  early 
stages  of  chloroform  and  alcohol  poisoning;  (6)  on  division  of  the  cer- 
vical sympathetic  or  stimulation  of  the  third  nerve. 

Dilatation  of  the  pupil  occurs  (1)  in  a  dim  light;  (2)  when  the  eye  is 
focussed  for  distant  objects;  (3)  on  the  local  application  of  atropine  and 
its  allied  alkaloids;  (4)  on  the  internal  administration  of  atropine  and  its 
allies;  (5)  in  the  later  stages  of  poisoning  by  chloroform,  opium,  and 
other  drugs;  (6)  on  paralysis  of  the  third  nerve;  (?)  on  stimulation  of 
the  cervical  sympathetic,  or  of  its  centre  in  the  floor  of  the  front  of  the 
aqueduct  of  Sylvius.  The  contraction  of  the  pupil  appears  to  be  under 
the  control  of  a  centre  in  the  medulla  or  on  the  corpora  quadrigemina, 
and  this  is  reflexly  stimulated  by  a  bright  light,  and  the  dilatation  when 
the  reflex  centre  is  not  in  action  is  due  to  the  more  powerful  sympathetic 
action;  but  in  addition,  it  appears  that  both  contraction  and  dilatation 
may  be  produced  by  a  local  mechanism,  upon  which  certain  drugs 
can  act,  which  is  independent  of  and  probably  often  antagonistic  to  the 
action  of  the  central  apparatus  of  the  third  and  sympathetic  nerve.  The 
action  of  the  fifth  nerve  upon  the  pupil  is  not  well  understood,  but  its 
apparent  effect  in  producing  dilatation  is  due  to  the  mixture  of  sympa- 
thetic fibres  with  its  nasal  branch.  The  sympathetic  influence  upon  the 
radiating   fibres   is  believed   to   be  conveyed   not   by  the  long   ciliary 


596  HANDBOOK    OF    PHYSIOLOGY. 

branches  of  that  nerve,  but  by  the  short  ciliary  branches  from  the  oph- 
thalmic ganglion. 

The  close  sympathy  subsisting  between  the  two  eyes  is  nowhere  better 
shown  than  by  the  condition  of  the  pupil.  If  one  eye  be  shaded  by  the 
hand  its  pupil  will  of  course  dilate;  but  the  pupil  of  the  other  eye  will 
also  dilate,  though  it  is  unshaded. 

Ciliary  Muscle. — The  ciliary  muscle  is  composed  of  plain  muscular 
fibres,  which  form  a  narrow  zone  around  the  interior  of  the  eyeball,  near 
the  line  of  junction  of  the  cornea  with  the  sclerotic,  and  just  behind  the 
outer  border  of  the  iris.  The  outermost  fibres  of  this  muscle  are  at- 
tached in  front  to  the  inner  part  of  the  sclerotic  and  cornea  at  their  line 
of  junction,  and  diverging  somewhat,  are  fixed  to  the  ciliary  processes, 
and  a  small  portion  of  the  choroid  immediately  behind  them.  The 
inner  fibres  immediately  within  the  preceding,  form  a  circular  zone 
around  the  interior  of  the  eyeball,  outside  the  ciliary  processes.  They 
compose  the  ring  formerly  called  the  ciliary  ligament. 

Accommodation. 

The  distinctness  of  the  image  formed  upon  the  retina,  is  mainly  de- 
pendent on  the  rays  emitted  by  each  luminous  point  of  the  object  being 
brought  to  a  perfect  focus  upon  the  retina.  If  this  focus  occur  at  a 
point  either  in  front  of,  or  behind  the  retina,  indistinctness  of  vision 
ensues,  with  the  production  of  a  halo.  The  focal  distance,  i.  e.,  the  dis- 
tance of  the  point  at  which  the  luminous  rays  from  a  lens  are  collected, 
besides  being  regulated  by  the  degree  of  convexity  and  density  of  the 
lens,  varies  with  the  distance  of  the  object  from  the  lens,  being  greater 
as  this  is  shorter,  and  vice  versa.  Hence,  since  objects  placed  at  various 
distances  from  the  eye  can,  within  a  certain  range,  different  in  different 
persons,  be  seen  with  almost  equal  distinctness,  there  must  be  some  pro- 
vision by  which  the  eye  is  enabled  to  adapt  itself,  so  that  whatever  length 
the  focal  distance  may  be,  the  focal  point  may  always  fall  exactly  upon 
the  retina. 

This  power  of  adaptation  of  the  eye  to  vision  at  different  distances  has 
received  the  most  varied  explanations.  It  is  obvious  that  the  effect 
might  be  produced  in  either  of  two  ways,  viz.,  by  altering  the  convexity 
and  thus  the  refracting  power,  either  of  the  cornea  or  lens;  or  by  chang- 
ing the  position  either  of  the  retina  or  of  the  lens,  so  that  whether  the 
object  viewed  be  near  or  distant,  and  the  focal  distance  thus  increased 
or  diminished,  the  focal  points  to  which  the  rays  are  converged  by  the 
lens  may  always  be  at  the  place  occupied  by  the  retina.  The  amount  of 
either  of  these  changes  required  in  even  the  widest  range  of  vision,  is 
extremely  small.  For,  from  the  refractive  powers  of  the  media  of  the 
eye,  the  difference  between  the  focal  distances  of  the  images  of  an  object 
at  such  a  distance  that  the  rays  are  parallel,  and  of  one  at  the  distance 


THE    SENSES. 


597 


of  four  inches,  is  only  about  0.143  of  an  inch.  On  this  calculation,  the 
change  in  the  distance  of  the  retina  from  the  lens  required  for  vision  at 
all  distances,  supposing  the  cornea  and  lens  to  maintain  the  same  form, 
would  not  be  more  than  about  one  line. 

It  is  now  almost  universally  believed  that  Helmholtz  is  right  in  his 
statement  that  the  immediate  cause  of  the  adaptation  of  the  eye  for  ob- 
jects at  different  distances  is  a  varying  shape  of  the  lens,  its  front  surface 
becoming  more  or  less  convex,  according  to  the  distance  of  the  object 
looked  at.  The  nearer  the  object,  the  more  convex  does  the  front  sur- 
face of  the  lens  become,  and  viceversd;  the  back  surface  taking  little  or 
no  share  in  the  production  of  the  effect  required.  The  following  simple 
experiment  illustrates  this  point.     If  a  small  flame  be  held  a  little  to  one 


Fig.  404. 


Fig.  405. 


Fro.  404.— Diagram  showing  three  reflections  of  a  candle.  1,  From  the  anterior  surface  of  cor- 
nea; 2,  from  the  anterior  surface  of  lens;  3,  from  the  posterior  surface  of  lens.  For  further  ex- 
planation, see  text.  The  experiment  is  best  performed  by  employing  an  instrument  invented  by 
Helmholtz,  termed  a  Phakoscope. 

Fig  .  405.  -  Phakoscope  of  Helmholtz.  At  B  B'  are  two  prisms,  by  which  the  light  of  a  candle  is 
concentrated  on  the  eye  of  the  person  experimented  with  at  C  ;  A  is  the  aperture  for  the  eye  of  the 
observer.  The  observer  notices  three  double  images,  as  in  Fig.  404,  reflected  from  the  eye  under 
examination  when  the  eye  is  fixed  upon  a  distant  object;  the  position  of  the  images  having  been 
noticed  the  eye  is  then  made  to  focus  a  near  object,  such  as  a  reed  pushed  up  by  C ;  the  images  from 
the  anterior  surfaces  of  the  lens  will  be  observed  to  move  towards  each  other,  in  consequence  of 
the  lens  becoming  more  convex. 

side  of  a  person's  eye,  an  observer  looking  at  the  eye  from  the  other  side 
sees  three  distinct  images  of  the  flame  (Fig.  404).  The  first  and  bright- 
est is  (1)  a  small  erect  image  formed  by  the  anterior  convex  surface  of 
the  cornea:  the  second  (2)  is  also  erect,  but  larger  and  less  distinct  than 
the  preceding,  and  is  formed  at  the  anterior  convex  surface  of  the  lens: 
the  third  (3)  is  smaller  and  reversed,  it  is  formed  at  the  posterior  surface 
of  the  lens,  which  is  concave  forwards,  and  therefore,  like  all  concave 


598  HANDBOOK    OF   PHYSIOLOGY. 

mirrors,  gives  a  reversed  image.  If  now  the  eye  under  observation  be  made 
to  look  at  a  near  object,  the  second  image  becomes  smaller,  clearer,  and 
approaches  the  first.  If  the  eye  be  now  adjusted  for  a  far  point,  the 
second  image  enlarges  again,  becomes  less  distinct,  and  recedes  from  the 
first.  In  both  cases  alike  the  first  and  third  images  remain  unaltered  in 
size  and  relative  position.  This  proves  that  during  accommodation  for 
near  objects  the  curvature  of  the  cornea,  and  of  the  posterior  of  the  lensr 
remains  unaltered,  while  the  anterior  surface  of  the  lens  becomes  more 
convex  and  approaches  the  cornea. 

Mechanism. — Of  course  the  lens  has  no  inherent  power  of  contrac- 
tion, and  therefore  its  changes  of  outlines  must  be  produced  by  some 
power  from  without;  and  there  seems  no  reason  to  doubt  that  this  power 
is  supplied  by  the  ciliary  muscle.  It  is  sometimes  termed  the  tensor 
choroidecB.  As  this  name  implies,  from  its  attachment,  it  is  able  to 
draw  forwards  the  choroid  and  therefore  slackens  the  tension  of  the  sus- 


Fig.  406.— Diagram  representing  by  dotted  lines  the  alteration  in  the  shape  of  the  lens  on  ac- 
commodation for  near  objects.    (E.  Landolt.) 

pensory  ligament  of  the  lens  which  arises  from  it.  The  lens  is  usually 
partly  flattened  by  the  action  of  the  suspensory  ligament;  and  the  ciliary 
muscle  by  diminishing  the  tension  of  this  ligament  diminishes,  to  a  pro- 
portional degree,  the  flattening  of  which  it  is  the  cause.  On  diminution 
or  cessation  of  the  action  of  the  ciliary  muscle,  the  lens  returns,  in  a 
corresponding  degree,  to  its  former  shape,  by  virtue  of  the  elasticity  of 
its  suspensory  ligament  (Fig.  406).  From  this  it  will  appear  that  the 
eye  is  usually  focussed  for  distant  objects.  In  viewing  near  objects  the 
pupil  contracts,  the  opposite  effect  taking  place  on  withdrawal  of  the 
attention  from  near  objects,  and  fixing  it  on  those  distant. 

Range  of  Distinct  Vision.  Near-point. — In  every  eye  there  is  a 
limit  to  the  power  of  accommodation.  If  a  book  be  brought  nearer  and 
nearer  to  the  eye,  the  type  at  last  becomes  indistinct  and  cannot  be 
brought  into  focus  by  any  effort  of  accommodation,  however  strong. 
This,  which  is  termed  the  near-point,  can  be  determined  by  the  follow- 


THE    SENSES.  599 

ing  experiment  (Schemer).  Two  small  holes  are  pricked  in  a  card  with 
a  pin  not  more  than  a  line  apart,  at  any  rate  their  distance  from  each 
other  must  not  exceed  the  diameter  of  the  pupil.  The  card  is  held  close 
in  front  of  the  eye,  and  a  small  needle  viewed  through  the  pin-holes. 
At  a  moderate  distance  it  can  be  clearly  focussed,  but  when  brought 
nearer,  beyond  a  certain  point,  the  image  appears  double  or  at  any  rate 
blurred.  This  point  where  the  needle  ceases  to  appear  single  is  the  near- 
point.  Its  distance  from  the  eye  can  of  course  be  readily  measured.  It 
is  usually  about  5  or  6  inches.  In  the  accompanying  figure  (Fig.  407) 
the  lens  b  represents  the  eye;  ef  the  two  pin-holes  in  the  card,  nn  the 
retina;  a  represents  the  position  of  the  needle.  When  the  needle  is  at  a 
moderate  distance,  the  two  pencils  of  light  coming  from  e  and/,  are 
focussed  at  a  single  point  on  the  retina  nn.  If  the  needle  be  brought 
nearer  than  the  near-point,  the  strongest  effort  of  accommodation  is  not 
sufficient  to  focus  the  two  pencils,  they  meet  at  a  point  behind  the 
retina.  The  effect  is  the  same  as  if  the  retina  were  shifted  forward  to 
mm.     Two  images  h.g.  are  formed,  one  from  each  hole.     It  is  interesting 


Fig.  407. — Diagram  of  experiment  to  ascertain  the  minimum  distance  of  distinct  vision. 

to  note  that  when  two  images  are  produced,  the  lower  one  g  really  ap- 
pears in  the  position  q,  while  the  upper  one  appears  in  the  position  p. 
This  may  be  readily  verified  by  covering  the  holes  in  succession. 

Course  of  a  Ray  of  Light. — With  the  help  of  the  diagram,  repre- 
senting a  vertical  section  of  the  eye  from  before  backwards,  the  mode  in 
which,  by  means  of  the  refracting  media  of  the  eye,  an  image  of  an 
object  of  sight  is  thrown  on  the  retina,  maybe  rendered  intelligible. 
The  rays  of  the  cones  of  light  emitted  by  the  points  A  b,  and  every  other 
point  of  an  object  placed  before  the  eye,  are  first  refracted,  that  is,  are 
bent  towards  the  axis  of  the  cone,  by  the  cornea  c  c,  and  the  aqueous 
humor  contained  between  it  and  the  lens.  The  rays  of  each  cone  are 
again  refracted  and  bent  still  more  towards  its  central  ray  or  axis  by  the 
anterior  surface  of  the  lens  E  e;  and  again  as  they  pass  out  through  its 
posterior  surface  into  the  less  dense  medium  of  the  vitreous  humor.  For 
a  lens  has  the  power  of  refracting  and  causing  the  convergence  of  the 
rays  of  a  cone  of  light,  not  only  on  their  entrance  from  a  rarer  medium 
into  its  anterior  convex  surface,  but  also  at  their  exit  from  its  posterior 
convex  surface  into  the  rarer  medium. 


■600 


HANDBOOK    OF    PHYSIOLOGY, 


In  this  manner  the  rays  of  the  cones  of  light  issuing  from  the  points 
a  and  B  are  again  collected  to  points  a  and  b;  and,  if  the  retina  F  be 
situated  at  a  and  b,  perfect,  though  reversed,  images  of  the  points  a  and 
B  will  be  formed  upon  it:  but  if  the  retina  be  not  at  a  and  b,  but  either 
before  or  behind  that  situation, — for  instance  at  H  or  G, — circular  lumi- 
nous spots  c  and/,  or  e  and  o,  instead  of  points,  will  be  seen;  for  at  h 
the  rays  have  not  yet  met,  and  at  g  they  have  already  intersected  each 
other,  and  are  again  diverging. 

The  retina  must  therefore  be  situated  at  the  proper  focal  distance 
from  the  lens,  otherwise  a  defined  image  will  not  be  formed;  or,  in  other 


Fig.  408.— Diagram  of  the  course  of  a  ray  of  light,  to  show  how  a  blurred  or  indistinct  image  is 
formed  if  the  object  be  not  exactly  f  ocussed  upon  retina. 

words,  the  rays  emitted  by  a  given  point  of  the  object  will  not  be  col- 
lected into  corresponding  point  of  focus  upon  the  retina. 


Defects  in  the  Optical  Apparatus. 

A.  Defects  in  the  Refracting  Media.— Under  this  head  we  may 
consider  the  defects  known  as  (1)  Myopia,  (2)  Hypermetropia,  (3)  As- 
tigmatism, (4)  Spherical  Aberration,  (5)  Chromatic  Aberration. 

The  normal  (emmetropic)  eye  is  so  adjusted  that  parallel  rays  are 
brought  exactly  to  a  focus  on  the  retina  without  any  effort  of  accommo- 
dation (i,  Fig.  409).  Hence  all  objects  except  near  ones  (practically  all 
objects  more  than  twenty  feet  off)  are  seen  without  any  effort  of  accom- 
modation; in  other  words,  the  far-point  of  the  normal  eye  is  at  an  infinite 
distance.  In  viewing  near  objects  we  are  conscious  of  an  effort  (the 
contraction  of  the  ciliary  muscle)  by  which  the  anterior  surface  of  the 
lens  is  rendered  more  convex,  and  the  rays  which  would  otherwise  be 
f  ocussed  behind  the  retina  are  converged  upon  the  retina  (see  dotted  lines 
2,  Fig.  408). 

1.  Myopia  (short-sight)  (4,  Fig.  409). — This  defect  is  due  to  an  ab- 
normal elongation  of  the  eye-ball.  The  eye  is  usually  larger  than  nor- 
mal and  is  always  longer  than  normal;  the  lens  is  also  probably  too 
convex.  The  retina  is  too  far  from  the  lens  and  consequently  parallel 
rays  are  focussed  in  front  of  the  retina,  and,  crossing,  form  little  circles 


THE    SENSES. 


601 


on  the  retina;  thus  the  images  of  distant  objects  are  blurred  and  indis- 
tinct. The  eye  is,  as  it  were,  permanently  adjusted  for  a  near-point. 
Rays  from  a  point  near  the  eye  are  exactly  focussed  iu  the  retina.  But 
those  which  issue  from  any  object  beyond  a  certain  distance  {far-point) 
cannot  be  distinctly  focussed.  This  defect  is  corrected  by  concave  glasses 
which  cause  the  rays  entering  the  eye  to  diverge;  hence  they  do  not 
come  to  a  focus  so  soon.     Such  glasses  of  course  are  only  needed  to  give 


tt,«  mo  Diaexams  showing- 1,  normal  (emmetropic)  eye  bringing  parallel  rays >  exactly  to a 
*  £*£.  fh«™Snf?T 3  eve  adapted  to  a  near  point;  without  accommodation  the  rayswould 
focus  on  the  J6™*-  i JSS  S»t  hr  mneadne  the  curvature  of  the  anterior  surface  of  the  lens 
KfS^»AM&?ftS^a5toS3SS§^^SSS  Cafl  indicated  by  the  meeting  of  the 
fshown  by  ^."^MS  in  this  case  the  axis  of  the  eye  is  shorter,  and  the  lens 
«W^thn,  norma'  :  mm  lei  'ays  are  focussed  behind  the  retina;  4,  myopic  eye;  in  this  case  the 
Xtatf  the"eye  is  abnCmafly  long,  and  the  lens  too  convex;  parallel  rays  are  focussed  in  front  ot 
the  retina. 

a  clear  vision  of  distant  objects.     For  near  objects,  except  in  extreme 
cases,  they  are  not  required. 

2.  Hypermetropia  (long-sight)  (3,  Fig.  409).—  This  is  the  reverse 
defect.  The  eve  is  too  short  and  the  lens  too  flat.  Parallel  rays  are 
focussed  behind  the  retina;  an  effort  of  accommodation  is  required  to 
focus  even  parallel  rays  on  the  retina;  and  when  they  are  divergent,  as 


602  HANDBOOK    OF    PHYSIOLOGY. 

in  viewing  a  near  object,  the  accommodation  is  insufficient  to  focus 
them.  Thus  in  well-marked  cases  distant  objects  require  an  effort  of 
accommodation  and  near  ones  a  very  powerful  effort.  Thus  the  ciliary 
muscle  is  constantly  acting.  This  defect  is  obviated  by  the  use  of  convex 
glasses,  which  render  the  pencils  of  light  more  convergent.  Such  glasses 
are  of  course  especially  needed  for  near  objects,  as  in  reading,  etc.  They 
rest  the  eye  by  relieving  the  ciliary  muscle  from  excessive  work. 

3.  Astigmatism  — This  defect,  which  was  first  discovered  by  Airy, 
is  due  to  a  greater  curvature  of  the  eye  in  one  meridian  than  in  others. 
The  eye  may  be  even  myopic  in  one  plane  and  hypermetropic  in  others. 
Thus  vertical  and  horizontal  lines  crossing  each  other  cannot  both  be 
focussed  at  once;  one  set  stand  out  clearly  and  the  others  are  blurred  and 
indistinct.  This  defect,  which  is  present  in  a  slight  degree  in  all  eyes, 
is  generally  seated  in  the  cornea,  but  occasionally  in  the  lens  as  well;  it 
may  be  corrected  by  the  use  of  cylindrical  glasses  (?'.  <?.,  curved  only  in 
one  direction). 

4.  Spherical  Aberration. — The  rays  of  a  cone  of  light  from  an  ob- 
ject situated  at  the  side  of  the  field  of  vision  do  not  meet  all  in  the  same 
point,  owing  to  their  unequal  refraction;  for  the  refraction  of  the  rays 
which  pass  through  the  circumference  of  a  lens  is  greater  than  that  of 
those  traversing  its  central  portion.  This  defect  is  known  as  spherical 
aberration,  and  in  the  camera,  telescope,  microscope,  and  other  optical 
instruments,  it  is  remedied  by  the  interposition  of  a  screen  with  a  circu- 
lar aperture  in  the  path  of  the  rays  of  light,  cutting  off  all  the  marginal 
rays  and  only  allowing  the  passage  of  those  near  the  centre.  Such  cor- 
rection is  effected  in  the  eye  by  the  iris,  which  forms  an  annular  dia- 
phragm to  cover  the  circumference  of  the  lens,  and  to  prevent  the  rays 
from  passing  through  any  part  of  the  lens  but  its  centre  which  corre- 
sponds to  the  pupil.  The  posterior  surface  of  the  iris  is  coated  with 
pigment,  to  prevent  the  passage  of  rays  of  light  through  its  substance. 
The  image  of  an  object  will  be  most  defined  and  distinct  when  the  pupil 
is  narrow,  the  object  at  the  proper  distance  for  vision,  and  the  light 
abundant;  so  that,  while  a  sufficient  number  of  rays  are  admitted,  the 
narrowness  of  the  pupil  may  prevent  the  production  of  indistinctness  of 
the  image  by  spherical  aberration.  But  even  the  image  formed  by  the 
rays  passing  through  the  circumference  of  the  lens,  when  the  pupil  is 
much  dilated,  as  in  dark,  or  in  a  feeble  light,  may,  under  certain  cir- 
cumstances, be  well  defined. 

Distinctness  of  vision  is  further  secured  by  the  outer  surface  of  the 
retina  as  well  as  the  posterior  surface  of  the  iris  and  the  ciliary  processes, 
being  coated  with  black  pigment,  which  absorbs  any  rays  of  light  that 
may  be  reflected  within  the  eye,  and  prevents  their  being  thrown  again 
upon  the  retina  so  as  to  interfere  with  the  images  there  formed.  The 
pigment  of  the  retina  is  especially  important  in  this  respect;  for  with 


THE    SENSES.  60S 

the  exception  of  its  outer  layer  the  retina  is  very  transparent,  and  if  the 
surface  behind  it  were  not  of  a  dark  color,  but  capable  of  reflecting  the 
light,  the  luminous  rays  which  had  already  acted  on  the  retina  would  be 
reflected  again  through  it,  and  would  fall  upon  other  parts  of  the  same 
membrane,  producing  both  dazzling  from  excessive  light,  and  indistinct- 
ness of  the  images. 

5.  Chromatic  Aberration. — In  the  passage  of  light  through  an  or- 
dinary convex  lens,  decomposition  of  each  ray  into  its  elementary  colored 
parts  commonly  ensues,  and  a  colored  margin  appears  around  the  image 
owing  to  the  unequal  refraction  which  the  elementary  colors  undergo. 
In  optical  instruments  this,  which  is  termed  chromatic  aberration,  is 
corrected  by  the  use  of  two  or  more  lenses,  differing  in  shape  and  dens- 
ity, the  second  of  which  continues  or  increases  the  refraction  of  the  rays 
produced  by  the  first,  but  by  recombining  the  individual  parts  of  each 
ray  into  its  original  white  light,  corrects  any  chromatic  aberration  which 
may  have  resulted  from  the  first.  It  is  probable  that  the  unequal  re- 
fractive power  of  the  transparent  media  in  front  of  the  retina  may  be  the 
means  by  which  the  eye  is  enabled  to  guard  against  the  effect  of  chro- 
matic aberration.  The  human  eye  is  achromatic,  however,  only  so  long 
as  the  image  is  received  at  its  focal  distance  upon  the  retina,  or  so  long 
as  the  eye  adapts  itself  to  the  different  distances  of  sight.  If  either  of 
these  conditions  be  interfered  with,  a  more  or  less  distinct  appearance  of 
colors  is  produced. 

An  ordinary  ray  of  white  light  in  passing  through  a  prism,  is  re- 
fracted, i.  e.,  bent  out  of  its  course,  but  the  different  colored  rays  which 
go  to  make  up  white  light  are  refracted  in  different  degrees,  and  there- 
fore appear  as  colored,  bands  fading  off  into  each  other:  thus  a  colored 
band  known  as  the  "  spectrum  "  is  produced,  the  colors  of  which  are 
arranged  as  follows — red,  orange,  yellow,  green,  blue,  indigo,  violet;  of 
these  the  red  ray  is  the  least,  and  the  violet  the  most  refracted.  Hence, 
as  Ilelmholtz  has  shown,  a  small  white  object  cannot  be  accurately  fo- 
cussed  on  the  retina,  for  if  we  focus  for  the  red  rays,  the  violet  are  out 
of  focus,  and  vice  versa  :  such  objects,  if  not  exactly  focussed,  are  often 
seen  surrounded  by  a  pale  yellowish  or  bluish  fringe. 

For  similar  reasons  a  red  surface  looks  nearer  than  a  blue  one  at  an 
equal  distance,  because,  the  red  rays  being  less  refrangible,  a  stronger 
effort  of  accommodation  is  necessary  to  focus  them,  and  the  eye  is  ad- 
justed as  if  for  a  nearer  object,  and  therefore  the  red  surface  appears 
nearer. 

From  the  insufficient  adjustment  of  the  image  of  a  small  white  ob- 
ject, it  appears  surrounded  by  a  sort  of  halo  or  fringe.  This  phenome- 
non is  termed  Irradiation.  It  is  from  this  reason  that  a  white  square 
on  a  black  ground  appears  larger  than  a  black  square  of  the  same  size  on 
white  ground. 


604  HANDBOOK    OF   PHYSIOLOGY. 

As  an  optical  instrument,  the  eye  is  superior  to  the  camera  in  the  fol- 
lowing, among  many  other  particulars,  which  may  be  enumerated  in  de- 
tail. 1.  The  correctness  of  images  even  in  a  large  field  of  view.  2. 
The  simplicity  and  efficiency  of  the  means  by  which  chromatic  aberra- 
tion is  avoided.  3.  The  perfect  efficiency  of  its  adaptation  to  different 
distances.  In  the  photographic  camera,  it  is  well  known  that  only  a 
comparatively  small  object  can  be  accurately  focussed.  In  the  photo- 
graph of  a  large  object  near  at  hand,  the  upper  and  lower  limits  are 
always  more  or  less  hazy,  and  vertical  lines  appear  curved.  This  is  due 
to  the  fact  that  the  image  produced  by  a  convex  lens  is  really  slightly 
curved  and  can  only  be  received  without  distortion  on  a  slightly  curved 
concave  screen,  hence  the  distortion  on  a  flat  surface  of  ground  glass. 
It  is  different  with  the  eye,  since  it  possesses  a  concave  background, 
upon  which  the  field  of  vision  is  depicted,  and  with  which  the  curved 
form  of  the  image  coincides  exactly.  Thus,  the  defect  of  the  camera 
obscura  is  entirely  avoided;  for  the  eye  is  able  1o  embrace  a  large  field  of 
vision,  the  margins  of  which  are  depicted  distinctly  and  without  distor- 
tion. If  the  retina  had  a  plane  surface  like  the  ground  glass  plate  in  a 
camera,  it  must  necessarily  be  much  larger  than  is  really  the  case  if  we 
were  to  see  as  much;  moreover,  the  central  portion  of  the  field  of  vision 
alone  would  give  a  good  clear  picture.     (Bernstein.) 

B.  Defective  Accommodation — Presbyopia. — This  condition  is 
due  to  the  gradual  loss  of  the  power  of  accommodation  which  is  part 
of  the  general  decay  of  old  age.  In  consequence  the  patient  would  be 
obliged  in  reading  to  hold  his  book  further  and  further  away  in  order  to 
focus  the  letters,  till  at  last  the  letters  are  held  too  far  for  distinct  vision. 
The  defect  is  remedied  by  weak  convex  glasses,  which  are  very  commonly 
worn  by  old  people.  It  is  due  chiefly  to  the  gradual  increase  in  density 
of  the  lens,  which  is  unable  to  swell  out  and  become  convex  when  near 
objects  are  looked  at,  and  also  to  a  weakening  of  the  ciliary  muscle,  and 
a  general  loss  of  elasticity  in  the  parts  concerned  in  the  mechanism. 

Visual  Sensations. 

Excitation  of  the  Retina. — Light  is  the  normal  agent  in  the  ex- 
citation of  the  retina.  The  only  layer  of  the  retina  capable  of  reacting 
to  the  stimulus  is  the  rods  and  cones.  The  proofs  of  this  statement  may 
be  summed  up  thus  : — 

(1.)  The»  point  of  entrance  of  the  optic  nerve  into  the  retina,  where 
the  rods  and  cones  are  absent,  is  insensitive  to  light  and  is  called  the 
blind  spot.  The  phenomenon  itself  is  very  readily  demonstrated.  If 
we  direct  one  eye,  the  other  being  closed,  upon  a  point  at  such  a  distance 
to  the  side  of  any  object,  that  the  image  of  the  latter  must  fall  upon  the 
retina  at  the  point  of  entrance  of  the  optic  nerve,  this  image  is  lost  either 
instantaneously,  or  very  soon.  If,  for  example,  we  close  the  left  eye, 
and  direct  the  axis  of  the  right  eye  steadily  towards  the  circular  spot 
here  represented,  while  the  page  is  held  at  a  distance  of  about  six  inches 


THE    SENSES.  60S 

from  the  eye,  both  dot  and  cross  are  visible.  On  gradually  increasing 
the  distance  between  the  eye  and  the  object,  by  removing  the  book 
farther  and  farther  from  the  face.,  and  still  keeping  the  right  eye  steadily 
on  the  dot,  it  will  be  found  that  suddenly  the  cross  disappears  from 


view,  while  on  removing  the  book  still  further,  it  suddenly  comes  insight 
again.  The  cause  of  this  phenomenon  is  simply  that  the  portion  of  ret- 
ina which  is  occupied  by  the  entrance  of  the  optic  nerve,  is  quite  blind; 
and  therefore  that  when  it  alone  occupies  the  field  of  vision,  objects  cease 
to  be  visible.  (2.)  In  the  fovea  centralis  and  macula  lutea  which  contain 
rods  and  cones  but  no  optic  nerve-fibres,  light  produces  the  greatest 
effect.  In  the  latter,  cones  occur  in  larger  numbers,  and  in  the  former 
cones  without  rods  are  found,  whereas  in  the  rest  of  the  retina  which  is 
not  so  sensitive  to  light,  there  are  fewer  cones  than  rods.  We  may  con- 
clude, therefore,  that  cones  are  even  more  important  to  vision  than  rods. 
(3.)  If  a  small  lighted  candle  be  moved  to  and  fro  at  the  side  of  and  close 
to  one  eye  in  a  dark  room  while  the  eyes  look  steadily  forward  into  the 
darkness,  a  remarkable  branching  figure  {Purhinje's  figures)  is  seen  float- 
ing before  the  eye,  consisting  of  dark  lines  on  a  reddish  ground.  As  the 
candle  moves,  the  figure  moves  in  the  opposite  direction,  and  from  its 
whole  appearance  there  can  be  no  doubt  that  it  is  a  reversed  picture  of 
the  retinal  vessels  projected  before  the  eye.  The  two  large  branching 
arteries  passing  up  and  down  from  the  optic  disc  are  clearly  visible  to- 
gether with  their  minutest  branches.  A  little  to  one  side  of  the  disc,  in 
a  part  free  from  vessels,  is  seen  the  yellow  spot  in  the  form  of  a  slight 
depression.  This  remarkable  appearance  is  doubtless  due  to  shadows  of 
the  retinal  vessels  cast  by  the  caudle.  The  branches  of  these  vessels  are 
chiefly  distributed  in  the  nerve-fibre  and  ganglionic  layers ;  and  since 
the  light  of  the  candle  falls  on  the  retinal  vessels  from  in  front,  the 
shadow  is  cast  behind  them,  and  hence  those  elements  of  the  retina  which 
perceive  the  shadows  must  also  lie  behind  the  vessels.  Here,  then,  we 
have  a  clear  proof  that  the  light-perceiving  elements  of  the  retina  are  not 
the  fibres  of  the  optic  nerve  forming  the  innermost  layer  of  the  retina 
but  the  external  layers  of  the  retina,  almost  certainly  the  rods  and  cones, 
which  indeed  appear  to  be  the  special  terminations  of  the  optic  nerve- 
fibres. 

Duration  of  Visual  Sensations. — The  duration  of  the  sensation 
produced  by  a  luminous  impression  on  the  retina  is  always  greater  than 
that  of  the  impression  which  produces  it.  However  brief  the  luminous 
impression,  the  effect  on  the  retina  always  lasts  for  about  one-eighth  of 
a  second.     Thus,  supposing  an  object  in  motion,  say  a  horse,  to  be  re- 


600  HANDBOOK    OF  PHYSIOLOGY. 

vealed  on  a  dark  night  by  a  flash  of  lightning.  The  object  would  be  seen 
apparently  for  an  eighth  of  a  second,  but  it  would  not  appear  in  motion; 
because,  although  the  image  remained  on  the  retina  for  this  time,  it  was 
really  revealed  for  such  an  extremely  short  period  (a  flash  of  lightning 
heing  almost  instantaneous)  that  no  appreciable  movement  on  the  part 
of  the  object  could  have  taken  place  in  the  period  during  which  it  was 
revealed  to  the  retina  of  the  observer.  And  the  same  fact  is  proved  in  a 
reverse  way.  The  spokes  of  a  rapidly  revolving  wheel  are  not  seen  as 
distinct  objects,  because  at  every  point  of  the  field  of  vision  over  which 
the  revolving  spokes  pass,  a  given  impression  has  not  faded  before  an- 
other comes  to  replace  it.  Thus  every  part  of  the  interior  of  the  wheel 
appears  occupied. 

The  duration  of  the  after-sensation,  produced  by  an  object,  is  greater 
in  a  direct  ratio  with  the  duration  of  the  impression  which  caused  it. 
Hence  the  image  of  a  bright  object,  as  the  panes  of  a  window  through 
which  the  light  is  shining,  may  be  perceived  in  the  retina  for  a  consider- 
able period,  if  we  have  previously  kept  our  eyes  fixed  for  some  time  on 
it.  But  the  image  in  this  case  is  negative.  If,  however,  after  shutting 
the  eyes  for  some  time,  we  open  them  and  look  at  an  object  for  an  in- 
stant, and  again  close  them,  the  after  image  is  positive. 

Intensity  of  Visual  Sensations. — It  is  quite  evident  that  the  more 
luminous  a  body  the  more  intense  is  the  sensation  it  produces.  But  the 
intensity  of  the  sensation  is  not  directly  proportional  to  the  intensity  of 
the  luminosity  of  the  object.  It  is  necessary  for  light  to  have  a  certain 
intensity  before  it  can  excite  the  retina,  but  it  is  impossible  to  fix  an 
arbitrary  limit  to  the  power  of  excitability.  As  in  other  sensations,  so 
also  in  visual  sensations,  a  stimulus  may  be  too  feeble  to  produce  a  sen- 
sation. If  it  be  increased  in  amount  sufficiently  it  begins  to  produce  an 
effect  which  is  increased  on  the  increase  of  the  stimulation;  this  increase 
in  the  effect  is  not  directly  proportional  to  the  increase  in  the  excitation, 
but  according  to  Fechtier's  law,  "  as  the  logarithm  of  the  stimulus," 
i.  e.,  in  each  sensation,  there  is  a  constant  ratio  between  the  increase  in 
the  stimulus  and  the  increase  in  the  sensation,  this  constant  ratio  for 
each  sensation  expresses  the  least  perceptible  increase  in  the  sensation 
or  minimal  increment  of  excitation. 

This  law,  which  is  true  only  within  certain  limits,  may  be  best  under- 
stood by  an  example.  When  the  retina  has  been  stimulated  by  the  light  of 
one  candle,  the  light  of  two  candles  will  produce  a  difference  in  sensation 
which  can  be  distinctly  felt.  If,  however,  the  first  stimulus  had  been 
that  of  an  electric  light,  the  addition  of  the  light  of  a  candle  would 
make  no  difference  in  the  sensation.  So,  generally,  for  an  additional 
stimulus  to  be  felt,  it  may  be  proportionately  small  if  the  original 
stimulus  have  been  small,  and  must  be  greater  if  the  original  stimulus 


THE    SENSES.  607 

have  been  great.  The  stimulus  increases  as  the  ordinary  numbers, 
while  the  sensation  increases  as  the  logarithm. 

The  Ophthalmoscope. — Part  of  the  light  which  enters  the  eye  is 
absorbed,  and  produces  some  change  in  the  retina,  of  which  we  shall 
treat  further  on;  the  rest  is  reflected. 

Every  one  is  perfectly  familiar  with  the  fact  that  it  is  quite  impossible 
to  see  the  fundus  or  back  of  another  person's  eye  by  simply  looking  into 
it.  The  interior  of  the  eye  forms  a  perfectly  black  background  to  the 
pupil.  The  same  remark  applies  to  an  ordinary  photographic  camera, 
and  may  be  illustrated  by  the  difficulty  we  experience  in  seeing  into  a 
room  from  the  street  through  the  window,  unless  the  room  be  lighted 
within.  In  the  case  of  the  eye  this  fact  is  partly  due  to  the  feebleness 
of  the  light,  reflected  from  the  retina,  most  of  it  being  absorbed  by  the 
choroid,  as  mentioned  above;  but  far  more  to  the  fact  that  every  such 
ray  is  reflected  straight  back  to  the  source  of  light  (e.  g.,  candle),  and 
cannot,  therefore,  be  seen  by  the  unaided  eye  without  intercepting  the 
incident  light  from  the  candle,  as  well  as  the  reflected  rays  from  the 
retina.     This  difficulty  is  surmounted  by  the  use  of  the  ophthalmoscope. 

The  ophthalmoscope,  brought  into  use  by  Helmholtz,  consists  in 
its  simplest  form  of  a,  a  slightly  concave  mirror  of  metal  or  silvered 
glass  perforated  in  the  centre,  and  fixed  into  a  handle;  and  b,  a  bicon- 
vex lens  of  about  2|-3  inches  focal  length.  Two  methods  of  examining 
the  eye  with  this  instrument  are  in  common  use — the  direct  and  indirect; 
both  methods  of  investigation  should  be  employed.  A  normal  eye 
should  be  examined;  a  drop  of  a  solution  of  atropia  (two  grains  to  the 
ounce)  or  of  hom-atropia  hydrobromate,  should  be  instilled  about  twenty 
minutes  before  the  examination  is  commenced;  the  ciliary  muscle  is 
thereby  paralyzed,  the  power  of  accommodation  is  abolished,  and  the 
pupil  is  dilated.  This  will  materially  facilitate  the  examination;  but  it 
is  quite  possible  to  observe  all  the  details  to  be  presently  described  with- 
out the  use  of  this  drug.  The  room  being  now  darkened,  the  observer 
seats  himself  in  front  of  the  person  whose  eye  he  is  about  to  examine, 
placing  himself  upon  a  somewhat  higher  level.  A  brilliant  and  steady 
light  is  placed  close  to  the  left  ear  of  the  patient.  The  atropia  having 
been  put  into  the  right  eye  only  of  the  patient,  this  eye  is  examined. 
Taking  the  mirror  in  his  right  hand,  and  looking  through  the  central 
hole,  the  operator  directs  a  beam  of  light  into  the  eye  of  the  patient. 
A  red  glare,  known  as  the  reflex,  is  seen;  it  is  due  to  the  illumination  of 
the  retina.  The  patient  is  then  told  to  look  at  the  little  finger  of  the 
observer's  right  hand  as  he  holds  the  mirror;  to  effect  this,  the  eye  is 
rotated  somewhat  inwards,  and  at  the  same  time  the  reflex  changes  from 
red  to  a  lighter  color,  owing  to  the  reflection  from  the  optic  disc.  The 
observer  now  approximates  the  mirror,  and  with  it  his  eye  to  the  eye  of 
the  patient,  taking  care  to  keep  the  light  fixed  upon  the  pupil,  so  as  not 
to  lose  the  reflex.  At  a  certain  point,  which  varies  with  different  eyes, 
but  is  usually  when  there  is  an  interval  of  about  two  or  three  inches 
between  the  observed  and  observing  eye,  the  vessels  of  the  retina  will  lie- 
come  visible  as  lines   running  in  different  directions.     Distinguish  the 


60S 


HANDBOOK    OF    PHYSIOLOGY. 


smaller  and  brighter  red  arteries  from  the  larger  and  darker  colored 
veins.  Examine  carefully  the  fundus  of  the  eye,  *.  e.,  the  red  surface — 
until  the  optic  disc  is  seen;  trace  its  circular  outline,  and  observe  the 
small  central  white  spot,  the  porus  opticus,  or  physiological  pit :  near 
the  centre  is  the  central  artery  of  the  retina  breaking  up  upon  the  disc 
into  branches;  veins  also  are  present,  and  correspond  roughly  to  the 
course  of  the  arteries.  Trace  the  vessels  over  the  disc  on  to  the  retina. 
The  optic  disc  is  bounded  by  two  delicate  rings,  the  more  external  being 
the  choroidal,  whilst  the  more  internal  is  the  sclerotic  opening.  Some- 
what to  the  outer  side,  and  only  visible  after  some  practice,  is  the  yellow 
spot,  with  the  small  lighter-colored  fovea  centralis  in  its  centre.  This 
constitutes  the  direct  method  of  examination; 
by  it  the  various  details  of  the  fundus  are  seen 
as  they  really  exist,  and  it  is  this  method  which 
should  be  adopted  for  ordinary  use. 

If  the  observer  is  ametropic,  *'.  e.,  is  myopic 
or  hypermetropic,  he  will  be  unable  to  employ 
the  direct  method  of  examination  until  he  has 
remedied  his  defective  vision  by  the  use  of  pro- 
per glasses. 

In  the  indirect  method  the  patient  is  placed 
as  before,  and  the  operator  holds  the  mirror  in 
his  right  hand  at  a  distance  of  twelve  to  eighteen 
inches  from  the  patient's  right  eye.  At  the  same 
time  he  rests  his  little  finger  lightly  upon  the 

^  temple,  and  holding  the  lens  between  his  thumb 

W\  and  forefinger,  two  or  three  inches  in  front  of 
•'!^^^^^^^^m  the  patient's  eye,  directs  the  light  through  the 
lens  into  the  eye.  The  red  reflex,  and  subse- 
quently the  white  one,  having  been  gained,  the 
operator  slowly  moves  his  mirror,  and  with  it  his 
eye,  towards  or  away  from  the  face  of  the  pa- 
tient, until  the  outline  of  one  of  the  retinal  ves- 
sels becomes  visible,when  very  slight  movements 
on  the  part  of  the  operator  will  suffice  to  bring- 
into  view  the  details  of  the  fundus  above  de- 
scribed, but  the  image  will  be  an  inverted  one. 
The  lens  should  be  kept  fixed  at  a  distance  of  two 
or  three  inches,  the  mirror  being  alone  moved 
until  the  disc  becomes  visible:  should  the  image 
of  the  mirror,  however,  obscure  the  disc,  the  lens  may  be  slightly  tilted. 


Fig.  410. — The  ophthalmo- 
scope. The  small  upper  mir- 
ror is  for  direct,  the  larger  for 
indirect  illumination. 


Visual  Purple. — The  method  by  which  a  ray  of  light  is  able  to 
stimulate  the  endings  of  the  optic  nerve  in  the  retina  in  such  a  manner 
that  a  visual  sensation  is  perceived  by  the  cerebrum  is  not  yet  under- 
stood. It  is  supposed  that  the  change  effected  by  the  agency  of  the 
light  which  falls  upon  the  retina  is  in  fact  a  chemical  alteration  in  the 
protoplasm,  and  that  this  change  stimulates  the  optic  nerve-endings. 
The  discovery  of  a  certain  temporary  reddish-purple  pigmentation  of  the 
outer  limbs  of  the  retinal  rods  in  certain  animals  (e.  g.,  frogs)  which 
have  been  killed  in  the  dark,  forming  the  so-called  visual  purple,  ap- 


THE    SENSES.  609 

peared  likely  to  offer  some  explanation  of  the  matter,  especially  as  it  was 
also  found  that  the  pigmentation  disappeared  when  the  retina  was  ex- 
posed to  light,  and  re-appeared  when  the  light  was  removed,  and  also 
that  it  underwent  distinct  changes  of  color  when  other  than  white  light 
was  used.  The  visual  purple  cannot,  however,  be  absolutely  essential 
to  the  due  production  of  visual  sensations,  as  it  is  abseat  from  the 
retinal  cones,  and  from  the  macula  lutea  and  fovea  centralis  of  the 
human  retina,  and  does  not  appear  to  exist  at  all  in  the  retinas  of  some 
animals,  e.  g.,  bat,  dove,  and  hen,  which  are,  nevertheless,  possessed  of 
good  vision. 

If  the  operation  be  performed  quickly  enough,  the  image  of  an  ob- 
ject may  be  fixed  in  the  pigment  on  the  retina  by  soaking  the  retina  of 
an  animal,  which  has  been  killed  in  the  dark,  in  alum  solution. 

Electrical  Currents. — According  to  the  careful  researches  of 
Dewar  and  McKendrick,  and  of  Holmgren,  it  appears  that  the  stimulus 
of  light  is  able  to  produce  a  variation  of  the  natural  electrical  cur- 
rent of  the  retina.  The  current  is  at  first  increased  and  then  dimin- 
ished. McKendrick  believes  that  this  is  the  electrical  expression  of 
those  chemical  changes  in  the  retina  of  which  we  have  already  spoken. 

Visual  Perceptions  and  Judgments. 

Reversion  of  the  Image. — The  direction  given  to  the  rays  by 
their  reflection  is  regulated  by  that  of  the  central  ray,  or  axis  of  the 
cone,  towards  which  the  rays  are  bent.     The  image  of  any  point  of  an 


Fig.  411.— Diagram  of  the  formation  of  the  image  on  the  retina. 

object  is,  therefore,  as  a  rule  (the  exceptions  to  which  need  not  here  be 
stated),  always  formed  in  a  line  identical  with  the  axis  of  the  cone  of 
light,  as  in  the  line  of  b  a,  or  A  b  (Fig.  411),  so  that  the  spot  where  the 
image  of  any  point  will  be  formed  upon  the  retina  may  be  determined 
by  prolonging  the  central  ray  of  the  cone  of  light,  or  that  ray  which 
traverses  the  centre  of  the  pupil.  Thus  a  b  is  the  axis  or  central  ray  of 
the  cone  of  light  issuing  from  a;  b  a  the  central  ray  of  the  cone  of  light 
issuing  from  b;  the  image  of  A  is  formed  at  b,  the  image  of  b  at  a,  in 
the  inverted  position;  therefore  what  in  the  object  was  above  is  in  the 
image  below,  and  vice  versd — the  right-hand  part  of  the  object  is  in  the 
image  to  the  left,  the  left-hand  to  the  right.  If  an  opening  be  made  in 
39 


610  HANDBOOK    OF   PHYSIOLOGY. 

an  eye  at  its  superior  surface,  so  that  the  retina  can  be  seen  through  the 
vitreous  humor,  this  reversed  image  of  any  bright  object,  such  as  the 
windows  of  the  room,  may  be  perceived  at  the  bottom  of  the  eye.  Or 
still  better,  if  the  eye  of  any  albino  animal,  such  as  a  white  rabbit,  in 
which  the  coats,  from  the  absence  of  pigment,  are  transparent,  is  dis- 
sected clean,  and  held  with  the  cornea  towards  the  window,  a  ver}r  dis- 
tinct image  of  the  window  completely  inverted  is  seen  depicted  on  the 
posterior  translucent  wall  of  the  eye.  Volkmann  has  also  shown  that  a 
similar  experiment  may  be  successfully  performed  in  a  living  person 
possessed  of  large,  prominent  eyes,  and  an  unusually  transparent  scle- 
rotic. 

An  image  formed  at  any  point  of  the  retina  is  referred  to  a  point 
outside  the  eye,  lying  on  a  straight  line  drawn  from  the  point  on  the 
retina  outwards  through  the  centre  of  the  pupih  Thus  an  image  on  the 
left  side  of  the  retina  is  referred  by  the  mind  to  an  object  on  the  right 
side  of  the  eye,  and  vice  versa.  Thus  all  images  on  the  retina  are  men- 
tally, as  it  were,  projected  in  front  of  the  eye,  and  the  objects  are  seen 
erect  though  the  image  on  the  retina  is  reversed.  Much  needless  con- 
fusion and  difficulty  have  been  raised  on  this  subject  for  want  of  re- 
membering that  when  we  are  said  to  see  an  object,  the  mind  is  merely 
conscious  of  the  picture  on  the  retina,  and  when  it  refers  it  to  the  ex- 
ternal object,  or  "projects"  it  outside  the  eye,  it  necessarily  reverses  it 
and  sees  the  object  as  erect,  though  the  retinal  image  is  inverted.  This  is 
further  corroborated  by  the  sense  of  touch.  Thus  an  object  whose  pic- 
ture falls  on  the  left  half  of  the  retina  is  reached  by  the  right  hand,  and 
hence  is  said  to  lie  on  the  right.  Or,  again,  an  object  whose  image  is 
formed  on  the  upper  part  of  the  retina  is  readily  touched  by  the  feet, 
and  is  therefore  said  to  be  in  the  lower  part  of  the  field,  and  so  on. 

Hence  it  is,  also,  that  no  discordance  arises  between  the  sensations  of 
inverted  vision  and  those  of  touch,  which  perceives  everything  in  its 
erect  position;  for  the  images  of  all  objects,  even  of  our  own  limbs,  in 
the  retina,  are  equally  inverted,  and  therefore  maintain  the  same  rela- 
tive position. 

Even  the  image  of  our  hand,  while  used  in  touch,  is  seen  inverted. 
The  position  in  which  we  see  objects,  we  call,  therefore,  the  erect  posi- 
tion. A  mere  lateral  inversion  of  our  body  in  a  mirror,  where  the  right 
hand  occupies  the  left  of  the  image,  is  indeed  scarcely  remarked;  and 
there  is  but  little  discordance  between  the  sensations  acquired  by  touch 
in  regulating  our  movements  by  the  image  in  the  mirror,  and  those  of 
sight,  as,  for  example,  in  tying  a  knot  in  the  cravat.  There  is  some 
want  of  harmony  here,  on  account  of  the  inversion  being  only  lateral, 
and  not  complete  in  all  directions. 

The  perception  of  the  erect  position  of  objects  appears,  therefore,  to 
be  the  result  of  an  act  of  the  mind.     And  this  leads  us  to  a  considera- 


THE    SENSES.  611 

tion  of  the  several  other  properties  of  the  retina,  and  of  the  co-operation 
of  the  mind  in  the  several  other  parts  of  the  act  of  vision.  To  these 
belong  not  merely  the  act  of  sensation  itself  and  the  perception  of  the 
changes  produced  in  the  retina,  as  light  and  colors,  but  also  the  conver- 
sion of  the  mere  images  depicted  in  the  retina,  into  ideas  of  an  extended 
field  of  vision,  of  proximity  and  distance,  of  the  form  and  size  of  objects, 
of  the  reciprocal  influence  of  different  parts  of  the  retina  upon  each 
other,  the  simultaneous  action  of  the  two  eyes,  and  some  other  phe- 
nomena. 

Field  of  Vision. — The  actual  size  of  the  field  of  vision  depends  on 
the  extent  of  the  retina,  for  only  so  many  images  can  be  seen  at  anyone 
time  as  can  occupy  the  retina  at  the  same  time;  and  thus  considered,  the 
retina,  the  conditions  of  which  are  perceived  by  the  brain,  is  itself  the 
field  of  vision.  But  to  the  mind  of  the  individual  the  size  of  the  field 
of  vision  has  no  determinate  limits;  sometimes  it  appears  very  small,  at 
another  time  very  large;  for  the  mind  has  the  power  of  projecting  images 
on  the  retina  towards  the  exterior.  Hence  the  mental  field  of  vision  is 
very  small  when  the  sphere  of  the  action  of  the  mind  is  limited  to  im- 


Fia.  412.— Diagram  of  the  optical  angle. 

pediments  near  the  eye:  on  the  contrary,  it  is  very  extensive  when  the 
projection  of  the  images  on  the  retina  towards  the  exterior,  by  the  in- 
fluence of  the  mind,  is  not  impeded.  It  is  very  small  when  we  look  in- 
to a  hollow  body  of  small  capacity  held  before  the  eyes;  large  when  we 
look  out  upon  the  landscape  through  a  small  opening;  more  extensive 
when  we  look  at  the  landscape  through  a  window;  and  most  so  when  our 
view  is  not  com  fined  by  any  near  object.  In  all  these  cases  the  idea  which 
we  receive  of  the  size  of  the  field  of  vision  is  very  different,  although  its 
absolute  size  is  in  all  the  same,  being  dependent  on  the  extent  of  the 
retina.  Hence  it  follows,  that  the  mind  is  constantly  co-operating  in 
the  acts  of  vision,  so  that  at  last  it  becomes  difficult  to  say  what  belongs 
to  mere  sensation,  and  what  to  the  influence  of  the  mind.  By  a  mental 
operation  of  this  kind,  we  obtain  a  correct  idea  of  the  size  of  individual 
objects,  as  well  as  of  the  extent  of  the  field  of  vision.  To  illustrate  this, 
it  will  be  well  to  refer  to  Fig.  412. 

The  angle  x,  included  between  the  decussating  central  rays  of  two 
cones  of  light  issuing  from  different  points  of  an  object,  is  called  the 
optical  angle — angulus  opticus  sen  visorius.     This  angle  becomes  larger, 


612  HANDBOOK    OF   PHYSIOLOGY. 

the  greater  the  distance  between  the  points  A  and  b;  and  since  the  angles 
x  and  y  are  equal,  the  distance  between  the  points  a  and  h  in  the  image 
on  the  retina  increases  as  the  angle  becomes  larger.  Objects  at  different 
distances  from  the  eye,  but  having  the  same  optical  angles— for  example, 
the  objects,  c,  d,  and  e, — must  also  throw  images  of  equal  size  upon  the 
retina;  and,  if  they  occupy  the  same  angle  of  the  field  of  vision,  their 
image  must  occupy  the  same  spot  in  the  retina. 

Nevertheless,  these  images  appear  to  the  mind  to  be  of  very  unequal 
size  when  the  ideas  of  distance  and  proximity  come  into  play;  for,  from 
the  image  a  b,  the  mind  forms  the  conception  of  a  visual  space  extend- 
ing to  e,  d,  or  c,  and  of  an  object  of  the  size  which  that  represented  by 
the  image  on  the  retina  appears  to  have  when  viewed  close  to  the  eye, 
or  under  the  most  usual  circumstances. 

Estimation  of  Size. — Our  estimation  of  the  size  of  various  objects 
is  based  partly  on  the  visual  angle  under  which  they  are  seen,  but  much 
more  on  the  estimate  we  form  of  their  distance.  Thus  a  lofty  mountain 
many  miles  off  may  be  seen  under  the  same  visual  angle  as  a  small  hill 
near  at  hand,  but  we  infer  that  the  former  is  much  the  larger  object  be- 
cause we  know  it  is  much  further  off  than  the  hill.  Our  estimate  of  dis- 
tance is  often  erroneous,  and  consequently  the  estimate  of  size  also 
Thus  persons  seen  walking  on  the  top  of  a  small  hill  against  a  clear  twi- 
light sky  appear  unusually  large,  because  we  over-estimate  their  distance, 
and  for  similar  reasons  most  objects  in  a  fog  appear  immensely  magni- 
fied. The  same  mental  process  gives  rise  to  an  idea  of  depth  in  the  field 
of  vision,  this  idea  being  fixed  in  our  mind  principally  by  the  circum- 
stance that,  as  we  ourselves  move  forwards,  different  images  in  succes- 
sion become  depicted  in  our  retina,  so  that  we  seem  to  pass  between  these 
images,  which  to  the  mind  is  the  same  thing  as  passing  between  the  ob- 
jects themselves. 

The  action  of  the  sense  of  vision  in  relation  to  external  objects  is, 
therefore,  quite  different  from  that  of  the  sense  of  touch.  The  objects 
of  the  latter  sense  are  immediately  present  to  it;  and  our  own  body,  with 
which  they  come  into  contact,  is  the  measure  of  their  size.  The  part  of  a 
table  touched  by  the  hand  appears  as  large  as  the  part  of  the  hand  receiv- 
ing an  impression  from  it,  for  a  part  of  our  body  in  which  a  sensation  is 
excited,  is  here  the  measure  by  which  we  judge  of  the  magnitude  of  the 
object.  In  the  sense  of  vision,  on  the  contrary,  the  images  of  objects 
are  mere  fractions  of  the  objects  themselves  realized  upon  the  retina,  the 
extent  of  which  remains  constantly  the  same.  But  the  imagination, 
which  analyzes  the  sensations  of  vision,  invests  the  images  of  objects,  to- 
gether with  the  whole  field  of  vision  in  the  retina,  with  very  varying 
dimensions;  the  relative  size  of  the  image  in  proportion  to  the  whole 
field  of  vision,  or  the  affected  parts  of  the  retina  to  the  whole  retina, 
alone  remaining  unaltered. 


THE    SKXSKS.  613 

Estimation  of  Direction. — The  direction  in  which  an  object  is 
seen  depends  on  the  part  of  the  retina  which  receives  the  image,  and  on 
the  distance  of  this  part  from,  and  its  relation  to,  the  central  point  of  the 
retina.  Thus,  objects  of  which  the  images  fall  upon  the  same  parts  of 
the  retina  lie  in  the  same  visual  direction;  and  when,  by  the  action  of 
the  mind,  the  images  or  affections  of  the  retina  are  projected  into  the 
exterior  world,  the  relation  of  the  images  to  each  other  remains  the  same. 

Estimation  of  Form. — The  estimation  of  the  form  of  bodies  by 
sight  is  the  result  partly  of  the  mere  sensation,  and  partly  of  the  asso- 
ciation of  ideas.  Since  the  form  of  the  images  perceived  by  the  retina 
depends  wholly  on  the  outline  of  the  part  of  the  retina  affected,  the  sen- 
sation alone  is  adequate  to  the  distinction  of  only  superficial  forms  of 
each  other,  as  of  a  square  from  a  circle.  But  the  idea  of  a  solid  body  as 
a  sphere,  or  a  body  of  three  or  more  dimensions,  e.  g.,  a  cube,  can  only 
be  attained  by  the  action  of  the  mind  constructing  it  from  the  different 
superficial  images  seen  in  different  positions  of  the  eye  with  regard  to 
the  object,  and,  as  shown  by  Wheatstone  and  illustrated  in  the  stereo- 
scope, from  two  different  prospective  projections  of  the  body  being  pre- 
sented simultaneously  to  the  mind  by  the  two  eyes.  Hence,  when,  in 
adult  age,  sight  is  suddenly  restored  to  persons  blind  from  infancy,  all 
objects  in  the  field  of  vision  appear  at  first  as  if  painted  flat  on  one  sur- 
face; and  no  idea  of  solidity  is  formed  until  after  long  exercise  of  the 
sense  of  vision  combined  with  that  of  touch. 

The  clearness  with  which  an  object  is  perceived  irrespective  of  accom- 
modation, would  appear  to  depend  largely  on  the  number  of  rods  and 
cones  which  its  retinal  image  covers.  Hence  the  nearer  an  object  is  to 
the  eye  (within  moderate  limits)  the  more  clearly  are  all  its  details  seen. 
Moreover,  if  we  want  carefully  to  examine  any  object,  we  always  direct 
the  eyes  straight  to  it,  so  that  its  image  shall  fall  on  the  yellow  spot 
where  an  image  of  a  given  area  will  cover  a  larger  number  of  cones 
than  anywhere  else  in  the  retina.  It  has  been  found  that  the  images  of 
two  points  must  be  at  least  t^-qt  in.  apart  on  the  yellow  spot  in  order 
to  be  distinguished  separately;  if  the  images  are  nearer  together,  the 
points  appear  as  one.  The  diameter  of  each  cone  in  this  part  of  the  ret- 
ina is  about  -nruTnr  m- 

Estimation  of  Movement. — We  judge  of  the  motion  of  an  object, 
partly  from  the  motion  of  its  image  over  the  surface  of  the  retina,  aud 
partly  from  the  motion  of  our  eyes  following  it.  If  the  image  upon  the 
retina  moves  while  our  eyes  and  our  body  are  at  rest,  we  conclude  that 
the  object  is  changing  its  relative  positiou  with  regard  to  ourselves.  In 
such  a  case  the  movement  of  the  object  may  be  apparent  only,  as  when 
we  are  standing  upon  a  body  which  is  in  motion,  such  as  a  ship.  If,  on 
the  other  hand,  the  image  does  not  move  with  regard  to  the  retina,  but 
remains  fixed  upon  the  same  spot  of  that  membrane,  while  our  eves  fol- 


614:  HANDBOOK    OF    PHYSIOLOGY. 

low  the  moving  body,  we  judge  of  the  motion  of  the  object  by  the  sen- 
sation of  the  muscles  in  action  to  move  the  eye.  If  the  image  moves 
over  the  surface  of  the  retina  while  the  muscles  of  the  eye  are  acting  at 
the  same  time  in  a  manner  corresponding  to  this  motion,  as  in  reading, 
we  infer  that  the  object  is  stationary,  and  we  know  that  we  are  merely 
altering  the  relations  of  our  eyes  to  the  object.  Sometimes  the  object 
appears  to  move  when  both  object  and  eye  are  fixed,  as  in  vertigo. 

The  mind  can,  by  the  faculty  of  attention,  concentrate  its  activity 
more  or  less  exclusively  upon  the  sense  of  sight,  hearing,  and  touch  al- 
ternately. When  exclusively  occupied  with  the  action  of  one  sense,  it  is 
scarcely  conscious  of  the  sensations  of  the  others.  The  mind,  when 
deeply  immersed  in  contemplations  of  another  nature,  is  indifferent  to 
the  actions  of  the  sense  of  sight,  as  of  every  other  sense.  We  often,  when 
deep  in  thought,  have  onr  eyes  open  and  fixed,  but  see  nothing,  because 
of  the  stimulus  of  ordinary  light  being  unable  to  excite  the  brain  to  per- 
ception, when  otherwise  engaged.  The  attention  which  is  thus  necessary 
for  vision,  is  necessary  also  to  analyze  what  the  field  of  vision  presents. 
The  mind  does  not  perceive  all  the  objects  presented  by  the  field  of  vision 
at  the  same  time  with  equal  acuteness,  but  directs  itself  first  to  one  and 
then  to  another.  The  sensation  becomes  more  intense,  according  as  the 
particular  object  is  at  the  time  the  principal  object  of  mental  contem- 
plation. Any  compound  mathematical  figure  produces  a  different  im- 
pression according  as  the  attention  is  directed  exclusively  to  one  or  the 
other  part  of  it.  Thus  in  Fig.  413,  we  may  in  succession  have  a  vivid 
perception  of  the  whole,  or  of  distinct  parts  only;  of  the  six  triangles 
near  the  outer  circle,  of  the  hexagon  in  the  middle,  or  of  the  three  large 
triangles.  The  more  numerous  and  varied  the  parts  of  which  a  figure 
is  composed,  the  more  scope  does  it  afford  for  the  play  of  the  attention. 
Hence  it  is  that  architectural  ornaments  have  an  enlivening  effect  on 
the  sense  of  vision,  since  they  afford  constantly  fresh  subject  for  the 
action  of  the  mind. 

Color  Sensations. — If  a  ray  of  sunlight  be  allowed  to  pass  through 
a  prism,  it  is  decomposed  by  its  passage  into  rays  of  different  colors, 
which  are  called  the  colors  of  the  spectrum;  they  are  red,  orange,  yellow, 
green,  blue,  indigo,  and  violet.  The  red  rays  are  the  least  turned  out  of 
their  course  by  the  prism,  and  the  violet  the  most,  whilst  the  other  colors 
occupy  in  order  places  between  these  two  extremes.  The  differences  in 
the  color  of  the  rays  depend  upon  the  number  of  vibrations  producing 
each,  the  red  rays  being  the  least  rapid  and  the  violet  the  most.  In 
addition  to  the  colored  rays  of  the  spectrum,  there  are  others  which  are 
invisible,  but  which  have  definite  properties,  those  to  the  left  of  the  red, 
and  less  refrangible,  being  the  calorific  rays  which  act  upon  the  ther- 
mometer, and  those  to  the  right  of  the  violet  which  are  called  actinic  or 


THE    SENSES. 


615 


chemical  rays,  which  have  a  powerful  chemical  action.  The  rays  which 
can  be  perceived  by  the  brain,  i.  e.,  the  colored  rays,  must  stimulate  the 
retina  in  some  special  manner  in  order  that  colored  vision  may  result, 
and  two  chief  explanations  of  the  method  of  stimulation  have  been 
suggested. 

(1.)  The  one,  originated  by  Young  and  elaborated  by  Helmholtz, 
holds  that  there  are  three  primary  colors,  viz.,  red,  green,  and  violet, 
and  that  in  the  retina  are  contained  rods  or  cones  which  answer  to  each 
of  these  primary  colors,  whereas  the  innumerable  intermediate  shades  of 
color  are  produced  by  stimulation  of  the  three  primary  and  color  termi- 
nals in  different  degrees,  the  sensation  of  white  is  produced  at  the  same 
time  when  the  three  elements  are  equally  excited.  Thus  if  the  retina  be 
stimulated  by  rays  of  certain  wave  length,  at  the  red  end  of  the  spec- 
trum, the  terminals  of  the  other  colors,  green  and  violet,  are  hardly 
stimulated  at  all,  but  the  red  terminals  are  strongly  stimulated,  the  re- 
sulting sensation  being  red.     The  orange  rays  excite  the  red  terminals 


Fio.  413. 

Fig.  414.— Diagram  of  the  three  primary  color  sensations.  (Young-Helmholtz  theory.)  1,  is 
the  red;  2,  green;  and  3,  violet,  primary  color  sensations.  The  lettering  indicates  the  colors  of  the 
spectrum.  The  diagram  indicates  by  the  height  of  the  curve  to  what  extent  the  several  primary 
sensations  of  color  are  excited  by  vibrations  of  different  wave  lengths. 

considerably,  the  green  rather  more,  and  the  violet  slightly,  the  resulting 
sensation  being  that  of  orange,  and  so  on. 

(2.)  The  second  theory  of  color  (Hering's)  supposes  that  there  are  six 
primary  color  sensations,  of  three  pair  of  antagonistic  or  complemental 
colors,  black  and  white,  red  and  green,  and  yellow  and  blue,  and  that 
these  are  produced  by  the  changes  either  of  disintegration  or  of  assimila- 
tion taking  place  in  certain  substances,  somewhat  it  may  be  supposed  of 
the  nature  of  the  visual  purple,  which  (the  theory  supposes  to)  exist  in 
the  retina.  Each  of  the  substances  corresponding  to  a  pair  of  colors,  be- 
ing capable  of  undergoing  two  changes,  one  of  construction  and  the  other 
of  disintegration,  with  the  result  of  producing  one  or  other  color.  For 
instance,  in  the  white-black  substance,  when  disintegration  is  in  excess 
of  construction  or  assimilation,  the  sensation  is  white,  and  when  assimi- 
lation is  in  excess  of  disintegration  the  reverse  is  the  case;  and  similarly 
with  the  red-green  substance,  and  with  the  yellow-blue  substance.  When 
the  repair  and  disintegration  are  equal  with  the  first  substance,  the  visual 


616  HANDBOOK    OF    THYSIOLOGY. 

sensation  is  gray;  but  in  the  other  pairs  when  this  is  the  case,  no  sensa- 
tion occurs.  The  rays  of  the  spectrum  to  the  left  produce  changes  in  the 
red-green  substance  only,  with  a  resulting  sensation  of  red,  whilst  the 
(orange)  rays  further  to  the  right  affect  both  the  red-green  and  the 
yellow-blue  substances;  blue  rays  cause  constructive  changes  in  the  yel- 
low-blue substance,  but  none  in  the  red-green,  and  so  on.  These  changes 
produced  in  the  visual  substances  in  the  retina  are  perceived  by  the  brain 
as  sensations  of  color. 

The  spectra  left  by  the  images  of  white  or  luminous  objects,  are  ordi- 
narily white  or  luminous;  those  left  by  dark  objects  are  dark.  Some- 
times, however,  the  relation  of  the  light  and  dark  parts  in  the  image  may. 
under  certain  circumstances,  be  reversed  in  the  spectrum;  what  was 
bright  may  be  dark,  and  what  was  dark  may  appear  light.  This  occurs 
whenever  the  eye,  which  is  the  seat  of  the  spectrum  of  a  luminous  object, 
is  not  closed,  but  fixed  upon  another  bright  or  white  surface,  as  a  white 
wall,  or  a  sheet  of  white  paper.     Hence  the  spectrum  of  the  sun,  which, 

red 

molet 


(blue 


Fig.  415.— Diagram  of  the  various  simple  and  compound  colors  of  light,  and  those  which  are 
complemental  of  each  other,  i.e.,  which,  when  mixed,  produce  a  neutral  gray  tint.  The  three 
simple  colors,  red,  yellow,  and  blue,  are  placed  at  the  angles  of  an  equilateral  triangle,  which  are 
connected  together  by  means  of  a  circle ;  the  mixed  colors,  green,  orange,  and  violet,  are  placed 
intermediate  between  the  corresponding  simple  or  homogeneous  colors;  and  the  complemental 
colors,  of  which  the  pigments,  when  mixed,  would  constitute  a  gray,  and  of  which  the  prismatic 
spectra  would  together  produce  a  white  light,  will  be  found  to  be  placed  in  each  case  opposite  to  each 
other,  but  connected  by  a  line  passing  through  the  centre  of  the  circle.  The  figure  is  also  useful  in 
showing  the  further  shades  of  color  which  are  complementary  of  each  other.  If  the  circle  be 
supposed  to  contain  every  transition  of  color  between  the  six  marked  down,  those  which  when 
united  yield  a  white  or  gray  color  will  always  be  found  directly  opposite  to  each  other;  thus,  for 
example,  the  intermediate  tint  between  orange  and  red  is  complementary  of  the  middle  tint  between 
green  and  blue. 

while  light  is  excluded  from  the  eye  is  luminous,  appears  black  or  gray 
when  the  eye  is  directed  upon  a  white  surface.  The  explanation  of  this 
is,  that  the  part  of  the  retina  which  has  received  the  luminous  image  re- 
mains for  a  certain  period  afterwards  in  an  exhausted  or  less  sensitive 
state,  while  that  which  has  received  a  dark  image  is  in  an  unexhausted, 
and  therefore  much  more  excitable  condition. 

The  ocular  spectra  which  remain  after  the  impression  of  colored 
objects  upon  the  retina  are  always  colored;  and  their  color  is  not  that  of 
the  object,  or  of  the  image  produced  directly  by  the  object,  but  the 
opposite,  or  complemental  color.  The  spectrum  of  a  red  object  is,  there- 
fore, green;  that  of  a  green  object,  red;  that  of  violet,  yellow;  that  of 


THE    SENSES.  h'17 

yellow,  violet,  and  so  on.  The  reason  of  this  is  obvious.  The  part  of 
the  retina  which  receives,  say,  a  red  image,  is  wearied  by  that  particular 
color,  but  remains  sensitive  to  the  other  rays  which  with  red  make  up 
white  light;  and,  therefore,  these  by  themselves  reflected  from  a  white 
object  produce  a  green  hue.  If,  on  the  other  hand,  the  first  object 
looked  at  be  green,  the  retina,  being  tired  of  green  rays,  receives  a  red 
image  when  the  eye  is  turned  to  a  white  object.  And  so  with  the  other 
colors;  the  retina  while  fatigued  by  yellow  rays  will  suppose  an  object  to 
be  violet,  and  vice  versa;  the  size  and  shape  of  the  spectrum  correspond- 
ing with  the  size  and  shape  of  the  original  object  looked  at.  The  colors 
which  thus  reciprocally  excite  each  other  in  the  retina  are  those  placed 
at  opposite  points  of  the  circle  in  Fig.  415.  The  peripheral  parts  of  the 
retina  have  no  perception  of  red.  The  area  of  the  retina  which  is 
capable  of  receiving  impressions  of  color  is  slightly  different  for  each 
color. 

Color  Blindness  or  Daltonism. — Daltonism  or  color-blindness  is  a 
by  no  means  uncommon  visual  defect.  One  of  the  commonest  forms  is 
the  inability  to  distinguish  between  red  and  green.  The  simplest  expla- 
nation of  such  a  condition  is,  that  the  elements  of  the  retina  which 
receive  the  impression  of  red,  etc.,  are  absent,  or  very  imperfectly  de- 
veloped, or,  according  to  the  other  theory,  that  the  red-green  substance 
is  absent  from  the  retina.  Other  varieties  of  color-blindness  in  which 
the  other  color-perceiving  elements  are  absent  have  been  shown  to  exist 
occasionally. 

Of  the  Reciprocal  Action  of  Different  Parts  of  the  Retina 

on  each  other. 

Although  each  elementary  part  of  the  retina  represents  a  distinct 
portion  of  the  field  of  vision,  yet  the  different  elementary  parts,  or  sensi- 
tive points  of  that  membrane,  have  a  certain  influence  on  each  other; 
the  particular  condition  of  one  influencing  that  of  another,  so  that  the 
image  perceived  by  one  part  is  modified  by  the  image  depicted  in  the 
other.  The  phenomena  which  result  from  this  relation  between  the  dif- 
ferent parts  of  the  retina,  may  be  arranged  in  two  classes:  the  one  in- 
cluding those  where  the  condition  existing  in  the  greater  extent  of  the 
retina  is  imparted  to  the  remainder  of  that  membrane;  the  other,  con- 
sisting of  those  in  which  the  condition  of  the  larger  portion  of  the  retina 
excites,  in  the  less  extensive  portion,  the  opposite  condition. 

1.  When  two  opposite  impressions  occur  in  contiguous  parts  of  an 
image  on  the  retina,  the  one  impression  is,  under  certain  circumstances, 
modified  by  the  other.  If  the  impressions  occupy  each  one-half  of  the 
image,  this  does  not  take  place;  for  in  that  case,  their  actions  are 
equally  balanced.  But  if  one  of  the  impressions  occupies  only  a  small 
part  of  the  retina,  and  the  other  the  greater  part  of  its  surface,  the  lat- 


618  HANDBOOK    OF    PHYSIOLOGY. 

ter  may,  if  long  continued,  extend  its  influence  over  the  whole  retina, 
so  that  the  opposite  less  extensive  impression  is  no  longer  perceived,  and 
its  place  becomes  occupied  by  the  same  sensation  as  the  rest  of  the  field 
of  vision.  Thus,  if  we  fix  the  eye  for  some  time  upon  a  strip  of  colored 
paper  lying  upon  a  white  surface,  the  image  of  the  colored  object,  espe- 
cially when  it  falls  on  the  lateral  parts  of  the  r.etina,  will  gradually  dis- 
appear, and  the  white  surface  be  seen  in  its  place. 

2.  In  the  second  class  of  phenomena,  the  affection  of  one  part  of  the 
retina  influences  that  of  another  part,  not  in  such  a  manner  as  to  oblit- 
erate it,  but  so  as  to  cause  it  to  become  the  contrast  or  opposite  to  itself. 
Thus  a  gray  spot  upon  a  white  ground  appears  darker  than  the  same 


Fig.  416.— Diagram  of  the  axes  of  rotation  to  the  eye.  The  thin  lines  indicate  axes  of  rotation, 
the  thick  the  position  of  muscular  attachment. 

tint  of  gray  would  do  if  it  alone  occupied  the  whole  field  of  vision,  and 
a  shadow  is  always  rendered  deeper  when  the  light  which  gives  rise  to  it 
becomes  more  intense,  owing  to  the  greater  contrast. 

The  former  phenomena  ensue  gradually,  and  only  after  the  images 
have  been  long  fixed  on  the  retina;  the  latter  are  instantaneous  in  their 
production,  and  are  permanent. 

In  the  same  way,  also,  colors  may  be  produced  by  contrast.  Thus,  a 
very  small  dull  gray  strip  of  paper,  lying  upon  an  extensive  surface  of 
any  bright  color,  does  not  appear  gray,  but  has  a  faint  tint  of  the  color 
which  is  the  complement  of  that  of  the  surrounding  surface.  A  strip 
of  gray  paper  upon  a  green  field,  for  example,  often  appears  to  have  a 
tint   of  red,  and  when  lying  upon  a  red  surface,  a  greenish  tint;  it 


THE    SENSES.  619 

has  an  orange-colored  tint  upon  a  bright  blue  surface,  and  a  bluish  tint 
upon  an  orange-colored  surface;  a  yellowish  color  upon  a  bright  violet, 
and  a  violet  tint  upon  a  bright  yellow  surface.  The  color  excited  thus, 
as  a  contrast  to  the  exciting  color,  being  wholly  independent  of  any  rays 
of  the  corresponding  color  acting  from  without  upon  the  retina,  must 
arise  as  an  opposite  or  antagonistic  condition  of  that  membrane;  and  the 
opposite  conditions  of  which  the  retina  thus  becomes  the  subject  would 
seem  to  balance  each  other  by  their  reciprocal  reaction.  A  necessary 
condition  for  the  production  of  the  contrasted  colors  is,  that  the  part  of 
the  retina  in  which  the  new  color  is  to  be  excited,  shall  be  in  a  state  of 
comparative  repose;  hence  the  small  object  itself  must  be  gray.  A  sec- 
ond condition  is,  that  the  color  of  the  surrounding  surface  shall  be  very 
bright,  that  is,  it  shall  contain  much  white  light. 

Movements  of  the  Eye. — The  eyeball  possesses  movement  around 
three  axes  indicated  in  Fig.  416,  viz.,  an  antero-posterior,  a  vertical,  and 
a  transverse,  passing  through  a  centre  of  rotation  a  little  behind  the 
centre  of  the  optic  axis.  The  movements  are  accomplished  by  pairs  of 
muscles. 

Direction  of  Movement.  By  what  muscles  accomplished* 

Inwards,     .....       Internal  rectus. 
Outwards,      ....  External  rectus. 

Upwards, j  Superior  rectus. 

r  ( Interior  oblique. 

•p.  •,  (  Inferior  rectus. 

Downwards,  .         .         .         .         ■{  a         .       ,v 

'  (  Superior  oblique. 

Inwards  and  upwards,         .         .    \  ITnt/rnal  "J*  suPerior  rectus' 
1  ( Interior  oolique. 

Inwards  and  downwards,         .        \  *nternal  a??. inferior  rectus' 

(  Superior  oblique. 

/-w   .     ,   -,         -,  ■,  External  and  superior  rectus. 

Outwards  and  upwards,       .         .    i  t  -e    •        vi- 

1  ( Interior  oblique. 

,-y   .    „   i         -,  -,  -,  \  External  and  inferior  rectus. 

Outwards  and  downwards,      .        ■{  a         •        ,  ,. 

(  Superior  oblique. 


Of  the  Simultaneous  Action   of  the  two  Eyes. 

Although  the  sense  of  sight  is  exercised  by  two  organs,  yet  the  im- 
pression of  an  object  conveyed  to  the  mind  is  single.  Various  theories 
have  been  advanced  to  account  for  this  phenomenon. 

By  Gall  it  was  supposed  that  we  do  not  really  employ  both  eyes 
simultaneously  in  vision,  but  always  see  with  only  one  at  a  time.  This 
especial  employment  of  one  eye  in  vision  certainly  occurs  in  persons 
whose  eyes  are  of  very  unequal  focal  distance,  but  in  the  majority  of  in- 
dividuals both  eyes  are  simultaneously  in  action,  in  the  perception  of  the 
same  object;  this  is  shown  by  the  double  images  seen  under  certain  condi- 


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HANDBOOK    OF    PHYSIOLOGY. 


tions.  If  two  fingers  be  held  up  before  the  eyes,  one  in  front  of  the 
other,  and  vision  be  directed  to  the  more  distant,  so  that  it  is  seen 
singly,  the  nearer  will  appear  double;  while,  if  the  nearer  one  be  regarded, 
the  most  distant  will  be  seen  double;  and  one  of  the  double  images  in 
each  case  will  be  found  to  belong  to  one  eye,  the  other  to  the  other  eye. 
Diplopia. — Single  vision  results  only  when  certain  parts  of  the  two 
retinae  are  affected  simultaneously;  if  different  parts  of  the  retinae  re- 


Fig.  417. 


•ceive  the  image  of  the  object,  it  is  seen  double.  This  may  be  readily  il- 
lustrated as  follows: — The  eyes  are  fixed  upon  some  near  object,  and  one 
of  them  is  pressed  by  the  thumb  so  as  to  be  turned  slightly  in  or  out; 


Fig.  418. 


Fig.  419. 


two  images  of  the  object  {Diplopia  or  Double  Vision)  are  at  once  per- 
ceived, just  as  is  frequently  the  case  in  persons  who  squint.  This  diplo- 
pia is  due  to  the  fact  that  the  images  of  the  object  do  not  fall  on  corre- 
sponding points  in  the  two  retinae. 

The  parts  of  the  retinae  in  the  two  eyes  which  thus  correspond  to 
each  other  in  the  property  of  referring  the  images  which  affect  them  si- 
multaneously to  the  same  spot  in  the  field  of  vision,  are,  in  man,  just 
those  parts  which  would  correspond  to  each  other,  if  one  retina  were 


THE    SENSES.  621 

placed  exactly  in  front  of,  and  over  the  other  (as  in  Fig.  417,  c).  Thus, 
the  outer  lateral  portion  of  one  eye  corresponds  to,  or,  to  use  a  better 
term,  is  identical  with  the  inner  portion  of  the  other  eye;  or  a  of  the  eye 
a  (Fig.  418),  with  a'  of  the  eye  B.  The  upper  part  of  one  retina  is 
also  identical  with  the  upjaer  part  of  the  other;  and  the  lower  parts  of 
the  two  eyes  are  identical  with  each  other. 

This  is  proved  by  a  simple  experiment.  Pressure  upon  any  part  of 
the  ball  of  the  eye,  so  as  to  affect  the  retina,  produces  a  luminous  circle, 
seen  at  the  opposite  side  of  the  field  of  vision  to  that  on  which  the  pres- 
sure is  made.  If,  now,  in  a  dark  room,  we  press  with  the  finger  at  the 
upper  part  of  one  eye,  and  at  the  lower  part  of  the  other,  two  luminous 
circles  are  seen,  one  above  the  other:  so,  also,  two  figures  are  seen  when 
pressure  is  made  simultaneously  on  the  two  outer  or  the  two  inner  sides  of 
both  eyes.  It  is  certain,  therefore,  that  neither  the  upper  part  of  one  retina 
and  the  lower  part  of  the  other  are  identical,  nor  the  outer  lateral  parts  of 
the  two  retina?  nor  their  iuner  lateral  portions.  But  if  jiressure  be  made 
with  the  fingers  upon  both  eyes  simultaneously  at  their  lower  part,  one 
luminous  ring  is  seen  at  the  middle  of  the  upper  part  of  the  field  of 
vision;  if  the  pressure  be  applied  to  the  upper  part  of  both  eyes  a  single 
luminous  circle  is  seen  in  the  middle  of  the  field  of  vision  below.  So, 
also,  if  we  press  upon  the  outer  side  a  of  the  eye  A,  and  upon  the  inner 
side  a'  of  the  eye  b,  a  single  spectrum  is  produced,  and  is  apparent  at 
the  extreme  right  of  the  field  of  vision;  if  upon  the  point  b  of  one  eye, 
and  the  point  V  of  the  other,  a  single  spectrum  is  seen  to  the  extreme 
left. 

The  spheres  of  the  two  retinae  may,  therefore,  be  regarded  as  lying 
one  over  the  other,  as  in  c,  Fig.  417;  so  that  the  left  portion  of  one  eye 
lies  over  the  identical  left  portion  of  the  other  eye,  the  right  portion  of 
one  eye  over  the  identical  right  portion  of  the  other  eye;  and  with  the 
upper  and  lower  portions  of  the  two  eyes,  a  lies  over  a',  b  over  b' ,  and  c 
over  & '.  The  points  of  the  one  retina  intermediate  between  a  and  c  are 
again  identical  with  the  corresponding  points  of  the  other  retina  between 
a'  and  c'j  those  between  b  and  c  of  the  one  retina,  with  those  between 
V  and  c'  of  the  other.  If  the  axes  of  the  eye,  a  and  b  (Fig.  419),  be  so 
directed  that  they  meet  at  a,  an  object  at  a  will  be  seen  singly,  for  the 
point  a  of  the  one  retina,  and  a'  of  the  other  are  identical.  So,  also,  if 
the  object  fi  be  so  situated  that  its  image  falls  in  both  eyes  at  the  same 
distance  from  the  central  point  of  the  retina, — namely,  at  b  in  the  one 
eye,  and  b'  in  the  other, — (5  will  be  seen  single,  for  it  affects  identical 
parts  of  the  two  retinas.     The  same  will  apply  to  the  object  y. 

In  quadrupeds,  the  relation  between  the  identical  and  non-identical 
parts  of  the  retina  cannot  be  the  same  as  in  man;  for  the  axes  of  their 
eyes  generally  diverge,  and  can  never  be  made  to  meet  in  one  point  of 
an  object.     When  an  animal  regards  an  object  situated  directly  in  front 


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HANDBOOK    OF    PHYSIOLOGY. 


of  it,  the  image  of  the  object  must  fall,  in  both  eyes,  on  the  outer  por- 
tion of  the  retinae.  Thus,  the  image  of  the  object  a  (Fig.  419)  will  fall 
at  a'  in  one,  and  at  a"  in  the  other:  and  these  points  a'  and  a"  must  be 
identical.  So,  also,  for  distinct  and  single  vision  of  objects  b  or  c, 
the  points  V  and  t"  or  c'  and  c" ',  in  the  two  retinae,  on  which  the  images 
of  these  objects  fall,  must  be  identical.  All  points  of  the  retina  in  each 
eye  which  receive  rays  of  light  from  lateral  objects  only,  can  have  no 
corresponding  identical  points  in  the  retina  of  the  other  eye;  for  other- 
wise two  objects,  one  situated  to  the  right  and  the  other  to  the  left, 
would  appear  to  lie  in  the  same  spot  of  the  field  of  vision.  It  is  probable, 
therefore,  that  there  are  in  the  eyes  of  animals,  parts  of  the  retinae  which 
are  identical,  and  parts  which  are  not  identical,  i.  e.,  parts  in  one  which 
have  no  corresponding  parts  in  the  other  eye.  And  the  relation  of  the 
two  retinae  to  each  other  in  the  field  of  vision  may  be  represented  as  in 
Fig.  420. 

Binocular  Vision. — The  cause  of  the  impressions  on  the  identical 
points  of  the  two  retinae  giving  rise  to  but  one  sensation,  and  the  per- 
ception of  a  single  image,  must  either  lie  in  the  structural  organization 
of  the  deeper  or  cerebral  portion  of  the  visual  apparatus,  or  be  the  result 

ABC 


Fig.  420.  Fig.  431. 

of  a  mental  operation;  for  in  no  other  case  is  it  the  property  of  the  cor- 
responding nerves  of  the  two  sides  of  the  body  to  refer  their  sensations 
as  one  to  one  spot. 

Many  attempts  have  been  made  to  explain  this  remarkable  relation 
between  the  eyes,  by  referring  it  to  anatomical  relation  between  the  op- 
tic nerves.  The  circumstance  of  the  inner  portion  of  the  fibres  of  the 
two  optic  nerves  decussating  at  the  commissure,  and  passing  to  the  eye 
of  the  opposite  side,  while  the  outer  portion  of  the  fibres  continue  their 
course  to  the  eye  of  the  same  side,  so  that  the  left  side  of  both  retinae  is 
formed  from  one  root  of  the  nerves,  and  the  right  side  of  both  retinae 
from  the  outer  root,  naturally  led  to  an  attempt  to  explain  the  phenom- 
enon by  this  distribution  of  the  fibres  of  the  nerves.  And  this  explana- 
tion is  favored  by  cases  in  which  the  entire  of  one  side  of  the  retina,  as 
far  as  the  central  point  in  both  eyes,  sometimes  becomes  insensible.  But 
Midler  shows  the  inadequateness  of  this  theory  to  explain  the  phenom- 
enon, unless  it  be  supposed  that  each  fibre  in  each  cerebral  portion  of  the 
optic  nerves  divides  in  the  optic  commissure  into  two  branches  for  the 


THE    SENSES. 


623 


identical  points  of  the  two  retinas,  as  is  shown  in  A,  Fig.  421.  But  there 
is  no  foundation  for  such  supposition. 

By  another  theory  it  is  assumed  that  each  optic  nerve  contains  ex- 
actly the  same  numher  of  fibres  as  the  other,  and  that  the  corresponding 
fibres  of  the  two  nerves  are  united  in  the  Sensorium  (as  in  Fig.  421,  B). 
But  in  this  theory  no  account  is  taken  of  the  partial  decussation  of  the 
fibres  of  the  nerves  in  the  optic  commissure. 

According  to  a  third  theory,  the  fibres  a  and  a' ,  Fig.  421,  C,  coming 
from  identical  points  of  the  two  retina?,  are  in  the  optic  commissure 
brought  into  one  optic  nerve,  and  in  the  brain  either  are  united  by  a 
loop,  or  spring  from  the  same  point.  The  same  disposition  prevails  in 
the  case  of  the  identical  fibres  b  and  b'.  According  to  this  theory,  the 
left  half  of  each  retina  would  be  represented  in  the  left  hemisphere  of 
the  brain,  and  the  right  half  of  each  retina  in  the  right  hemisphere. 

Another  explanation  is  founded  on  the  fact,  that  at  the  anterior  part 
of  the  commissure  of  the  optic  nerve,  certain  fibres  pass  across  from  the 


Fig.  422. 

distal  portion  of  one  nerve  to  the  corresponding  portion  of  the  other 
nerves,  as  if  they  were  commissural  fibres  forming  a  connection  between 
the  retinas  of  the  two  eyes.  It  is  supposed,  indeed,  that  these  fibres  may 
connect  the  corresponding  parts  of  the  two  retinae,  and  may  thus  ex- 
plain their  unity  of  action;  in  the  same  way  that  corresponding  parts  of 
the  cerebral  hemispheres  are  believed  to  be  connected  together  by  the 
commissural  fibres  of  the  corpus  callosum,  and  so  enabled  to  exercise 
unity  of  function. 

Judgment  of  Solidity. — On  the  whole,  it  is  probable,  that  the  power 
of  forming  a  single  idea  of  an  object  from  a  double  impression  conveyed 
by  it  to  the  eyes  is  the  result  of  a  mental  act.  This  view  is  supported  by 
the  same  facts  as  those  employed  by  Wheatstone  to  show  that  this  power 
is  subservient  to  the  purpose  of  obtaining  a  right  perception  of  bodies 
raised  in  relief.  When  an  object  is  placed  so  near  the  eyes  that  to  view 
it  the  optic  axes  must  converge,  a  different  perspective  projection  of  it 
is  seen  by  each  eye,  these  perspectives  being  more  dissimilar  as  the  con- 
vergence of  the  optic  axes  becomes  greater.  Thus,  if  any  figure  of  three 
dimensions,  an  outline  cube,  for  example,  be  held  at  a  moderate  distance 
before  the  eyes,  and  viewed  with  each  eye  successively  while  the  head  i> 


624  HANDBOOK    OF   PHYSIOLOGY. 

kept  perfectly  steady,  A  (Fig.  420)  will  be  the  picture  presented  to  the 
right  eye,  and  B  that  seen  by  the  left  eye.  Wheatstone  has  shown  that 
on  this  circumstance  depends  in  a  great  measure  our  conviction  of  the 
solidity  of  an  object,  or  of  its  projection  in  relief.  If  different  perspective 
drawings  of  a  solid  body,  one  representing  the  image  seen  by  the  right 
eye,  the  other  that  seen  by  the  left  (for  example,  the  drawing  of  a  cube, 
a,  B,  Fig.  422)  be  presented  to  corresponding  parts  of  the  two  retina?,  as 
may  be  readily  done  by  means  of  the  stereoscope,  the  mind  will  perceive 
not  merely  a  single  representation  of  the  object,  but  a  body  projecting 
in  relief,  the  exact  counterpart  of  that  from  which  the  drawings  were 
made. 

By  transposing  two  stereoscopic  pictures  a  reverse  effect  is  produced; 
the  elevated  parts  appear  to  be  depressed,  and  vice  versa.  An  instrument 
contrived  with  this  purpose  is  termed  a  pseudoscope.  Viewed  with  this 
instrument  a  bust  appears  as  a  hollow  mask,  and  as  may  readily  be  im- 
agined the  effect  is  most  bewildering. 


CHAPTER  XXI. 

THE  SYMPATHETIC  NERVOUS  SYSTEM. 

Having  in  the  preceding  chapters  completed  the  description  of  the 
Cerebro-spinal  nervous  system,  there  remains  to  be  considered  the  struc- 
ture and  functions  of  the  so-called  Sympathetic  nervous  system,  and  to 
this  it  is  now  necessary  to  direct  attention. 

It  should,  however,  be  borne  in  mind  that  the  cerebro-spinal  and 
sympathetic  systems  are  so  very  intimately  connected  that  the  separation 
of  the  one  from  the  other  may  be  considered  to  be  purely  for  the  sake 
of  convenience. 

Distribution. — The  various  ganglia  and  nerves  of  which  the  sympa- 
thetic system  is  generally  said  to  consist  have  been  already  enumerated. 
Gaskell's  researches  have  suggested  a  convenient  classification  of  the 
former  into:  (1.)  The  main  sympathetic  chain,  extending  from  above 
downwards,  in  the  form  of  connected  ganglia  lying  upon  the  bodies  of 
the  vertebrae,  which  may  be  called  lateral  or  vertebral  ganglia.  (2  ) 
A  more  or  less  distinct  chain,  prevertebral  in  position,  consisting  of  the 
semilunar,  inferior  mesenteric  and  similar  plexuses,  which  may  be 
called  collateral  ganglia.  (3.)  Ganglia  situated  in  the  organs  and  tis- 
sues themselves,  called  terminal  ganglia.  (4.)  The  ganglia  of  the  pos- 
terior roots  of  the  spinal  nerves. 

The  connection  between  these  parts  is  as  follows  :  the  visceral  branch 
or  ramus  communicans  of  each  spinal  nerve,  which  is  one  of  the  divi- 
sions of  a  typical  spinal  nerve — the  others  being  the  dorsal  and  ventral — 
passes  first  of  all  into  the  lateral  chain  ;  from  this  chain  branches,  rami 
'•fferentes,  pass  into  the  collateral  ganglia,  and  from  these  again  other 
blanches  pass  off  into  the  organs  to  end  in  the  terminal  ganglia.  In  the 
thoracic  region  the  rami  communicantes  are  composed  of  two  parts, 
white  and  gray.  The  former  can  be  traced  backwards  into  both  spinal 
nerve  roots  of  their  corresponding  spinal  nerve  ;  and  in  the  other  direc- 
tion partly  into  the  lateral  sympathetic  chain,  and  partly  into  the  great 
splanchnic  nerves  and  so  into  the  collateral  ganglia  without  entering  the 
lateral  chain  at  all.  The  upper  white  rami  (from  the  2d  to  5th).  how- 
ever, proceed  upwards  and  join  the  superior  cervical  ganglion,  instead  of 
passing  downwards  into  the  splanchnics.  Other  branches  go  downwards 
into  the  lumbar  and  sacral  plexuses.  The  gray  rami  of  nil  the  spinal 
40 


626 


HANDBOOK    OF    PHYSIOLOGY. 


Fig.  423. — Diagrammatic  view  of  the 
Sympathetic  cord  of  the  right  side,  show- 
ing its  connections  with  the  principa- 
cerebro-spinal  nerves  and  the  main  prael 
aortic  plexuses.  %.  (From.  Quain's 
Anatomy.) 

Cerebrospinal  nerves.— VL,  a  portion 
of  the  sixth  cranial  as  it  passes  through 
the  cavernous  sinus,  receiving  two  twigs 
from  the  carotid  plexus  of  the  sympathe- 
tic nerve ;  O,  ophthalmic  ganglion  con- 
nected by  a  twig  with  the  carotid  plexus; 
M,  connection  of  the  spheno-palatine 
ganglion  by  the  Vidian  nerve  with  the 
carotid  plexus;  C,  cervical  plexus;  Br, 
brachial  plexus;  D  6.  sixth  intercostal 
nerve;  D  12,  twelfth;  L  3,  third  lumbar 
nerve;  S  1,  first  sacral  nerve;  S  3,  third; 
S  5,  fifth;  Cr,  anterior  crural  nerve;  Cr, 
great  sciatic;  pn,  vagus  in  the  lower  part 
of  the  neck;  r,  recurrent  nerve  winding 
round  the  subclavian  artery. 

Sympathetic  Cord .—  c,  superior  cervi- 
cal ganglion;  c',  second,  or  middle;  <■■'', in- 
ferior: from  each  of  these  ganglia  cardiac 
nerves  (all  deep  on  this  side)  are  seen  de- 
scending to  the  cardiac  plexus;  d  1, 
placed  immediately  below  the  first  dorsal 
sympathetic  ganglion;  d  6,  is  opposite 
the  sixth;  1 1,  first  lumbar  ganglion;  c  g, 
the  terminal  or  coccygeal  ganglion. 

Prceaortic  and  Visceral  Plexuses.— pp, 
pharyngeal,  and,  lower  down,  laryngeal 
plexus;  pi,  post,  pulmonary  plexus 
spreading  from  the  vagus  on  the  back  of 
the  rightbronchus;  ca,  on  the  aorta,  the 
cardiac  plexus,^  towards  which,  in  addition 
to  the  cardiac  nerve  from  the  three  cer- 
vical sympathetic  ganglia,  other  branch- 
es are  seen  descending  from  the  vagus 
and  recurrent  nerves;  co,  right  or  poste- 
rior and  co',  left  or  ant.  coronary  plexus; 
o,  oesophageal  plexus  in  long  meshes  on 
the  gullet;  sp,  great  splanchnic  nerve 
formed  by  branches  from  the  fifth,  sixth, 
seventh,  eighth, and  ninth  dorsal  ganglia; 
+,  small  splanchnic  from  the  ninth  and 
tenth;  -\-  +,  smallest  or  thiril  splanchnic 
from  the  eleventh;  the  first  and  second  of 
these  are  shown  joining  the  solar  plexus, 
so;  the  third  descending  to  the  renal 
plexus,  re;  connecting  branches  between 
the  solar  plexus  and  the  vagi  are  also  rep- 
resented; pn',  above  the  place  where  the 
right  vagus  passes  to  the  lower  or  pos- 
terior surface  of  the  stomach;  pn",  the 
left  distributed  on  the  anterior  or  upper 
surface  of  the  cardiac  portion  of  the  or- 
gan: from  the  solar  plexus  large  branch- 
es are  seen  surrounding  the  arteries  of 
the  cceliac  axis,  and  descending  to  m  s, 
the  sup.  mesenteric  plexus ;  opposite  to 
this  is  an  indication  of  the  suprarenal 
plexus;  below  r  e  (the  renal  plexus),  the 
spermatic  plexus  is  also  indicated ;  a  o,  on 
the  front  of  the  aorta,  marks  the  aortic 
plexus,  formed  by  nerves  descending 
from  the  solar  and  sup.  mesenteric  plex- 
uses and  from  the  lumbar  ganglia;  mi, 
the  inf.  mesenteric  plexus  surrounding 
thecorresponding  artery ;  hy,  hypogastric 
plexus  placed  between  the  common  iliac 
vessels,  connected  above  with  the  aortic 
plexus,  receiving  nerves  from  the  lower 
lumbar  ganglia,  and  dividing  below  into 
the  right  and  left  pelvic  or  inf.  hypogas- 
tric plexuses;  pi,  the  right  pelvic  plexus; 
from  this  the  nerves  descending  are  join- 
ed by  those  from  the  plexus  on  the  sup. 
hemorrhoidal  vessels,  mi',  by  nerves  from 
the  sacral  ganglia,  and  by  visceral 
nerves  from  the  third  and  fourth  sacral 
spinal  nerves,  and  there  are  thus  formed 
the  rectal,  vesical,  and  other  plexuses,  which  ramify  upon  the  viscera,  as  towards  ir,  and  v,  the 
rectum  and  bladder. 


THE    SYMPATHETIC    NERVOUS    SVSTKM.  627 

rjerves  are  the  only  apparent  representatives  of  the  visceral  branches  in 
the  regions  above  the  2d  thoracic  nerve  root,  and  below  the  2d  lumbar 
nerve  root,  with  the  exception  of  the  roots  of  the  2d  and  3d  sacral 
nerves,  which  have  also  white  rami,  and  consist  of  non-medullated  fibres 
and  pass  from  the  ganglia  to  be  distributed  chiefly  to  the  spinal  column, 
to  the  spinal  membranes  and  to  the  spinal  nerve  roots  themselves.  We 
must  look  upon  the  white  rami  then  as  the  visceral  branches  proper. 

A  peculiarity  in  the  structure  of  these  white  medullated  visceral 
nerves  is  the  fineness  of  their  fibres.  They  area  third  or  a  fourth  of  the 
diameter  of  ordinary  medullated  fibres,  measuring  1.8yu  to  2.7 pi  instead 
of  14.4//  to  19yw.  They  are  a  peculiarity  of  the  spinal  nerve  roots  chiefly 
in  the  thoracic  region,  but  are  also  to  be  found  in  the  2d  and  3d  sacral 
nerves,  aud  constitute  there  the  nervi  erigentes  which  pass  directly  to 
the  hypogastric  plexus,  and  not  first  of  all  into  the  lateral  chain.  From 
this  plexus  branches  pass  upwards  into  the  inferior  mesenteric  ganglia 
and  downwards  to  the  bladder,  rectum  and  generative  organs.  These 
nerves,  called  by  Gaskell  pelvic  splanchnic  nerves,  differ  from  the  rami 
viscerales  of  the  thoracic  region  only  in  not  communicating  with  the 
lateral  ganglia;  the  branches  which  pass  upwards  from  the  thoracic  re- 
gion to  the  neck,  he  calls  cervical  splanchnics,  and  the  splanchnics 
proper  abdominal  splanchnics.  The  white  rami  viscerales  of  the  upper 
cervical  and  cervico-cranial  regions  do  not  run  with  their  corresponding 
gray  rami,  but  form,  Gaskell  thinks,  the  internal  branch  of  the  spinal 
accessory  nerve,  which  contains  small  medullated  fibres  similar  to  those 
of  the  visceral  branches  in  the  thoracic  region.  This  branch  passes 
into  the  ganglion  of  the  trunk  of  the  vagus.  Small  visceral  fibres  exist 
too  in  the  roots  of  the  vagus,  and  in  those  of  the  glosso-pharyngeal  in 
connection  with  the  ganglion  of  the  trunk  and  ganglion  petrosum,  as 
well  as  in  the  chorda  tympani,  in  the  small  petrosal  and  in  other  cranial 
visceral  nerves. 

Functions. — The  functions  of  the  sympathetic  system  are  not  by  any 
means  completely  understood.  Indeed,  until  within  the  last  few  years, 
what  could  be  said  about  them  was  of  a  very  vague  kind.  The  remarka- 
ble researches  of  Gaskell  have,  however,  done  much  to  clear  up  the 
former  confusion;  and  in  the  following  account  the  description  of  the 
functions  of  the  sympathetic  as  given  by  that  observer,  will  be  to  a  great 
extent  followed. 

A.  Functions  of  the  nerve  fibres. — The  efferent  nerve  fibres  of 
the  sympathetic  system  supply  (a)  the  muscles  of  the  vascular  sys- 
tem, to  which  they  send  vaso-motor  fibres,  i.  e.,  vaso-constrictor  and 
cardiac  augmentor  or  accelerator,  and  vaso-inhibitory  fibres,  i.  e.,  vaso- 
dilator and  cardiac  inhibitory;  (b)  the  muscles  of  the  viscera,  to  which 
they  send  both  viscero-motor  and  viscero-inhibitory  fibres,  (c)  The  se- 
cretory gland-cells. 


628  HANDBOOK    OF   PHYSIOLOGY. 

(a)  i.  Vaso-motor  or  Vaso-consirictor  and  Car  dio-aug  mentor  Fibres. 
— The  vaso-motor  nerves  for  all  parts  of  the  body  come  from  the  central 
nervous  system,  and  pass  out  from  the  spinal  cord  in  the  white  rami  vis- 
cerales  of  the  thoracic  region  from  the  2d  thoracic  to  the  2d  lumbar 
nerve  roots  inclusive,  as  fine  medullated  fibres;  they  then  pass  to  the 
lateral  or  main  sympathetic  chain,  become  non-medullated,  and  are  dis- 
tributed to  their  muscles  either  directly  or  through  terminal  ganglia. 
Thus  the  augmentor  nerves  of  the  heart  arise  in  the  thoracic  rami,  pass 
upwards,  aud  are  distributed  to  the  heart  through  the  ganglion  stellatum 
or  inferior  cervical  ganglion;  the  vaso-motor  nerves  for  the  arm  pass  out 
of  the  cord  below  the  origin  of  the  roots  of  the  brachial  plexus,  in  the 
anterior  roots  of  the  2d  and  lower  thoracic  nerves,  and  reach  that  plexus 
by  the  same  ganglion;  the  vaso-motor  nerves  of  the  foot  leave  the  spinal 
cord  high  up,  and  reach  the  sympathetic  lateral  ganglia  above  the  origin 
of  the  sciatic  nerve,  into  which  they  pass  through  the  abdominal  sympa- 
thetic. In  all  cases  the  nerves  lose  their  medulla  in  the  ganglia.  Simi- 
larly the  vaso-motor  nerve  supply  for  the  blood-vessels  of  the  head  and 
neck  and  of  the  abdomen  is  derived  from  the  cervical  and  abdominal 
splanchnics  respectively,  or  from  the  corresponding  rami  efferentes  of 
the  upper  lumbar  ganglia. 

The  lateral  sympathetic  chain  G-askell  proposes  to  call  the  chain  of 
vaso-motor  ganglia. 

ii.  Vaso-inhibitory  or  Vaso-dilator,  and  Oardio-inhibitory  Fibres. — 
Of  these,  which  are  doubtless  as  widely  distributed  as  the  vaso-motor 
fibres,  we  have  distinct  proof  in  the  existence  of  fibres  separate  from  vaso- 
motor, e.  g.,  in  the  inhibitory  nerve  of  the  heart,  the  cardio-vagus;  in 
the  chorda  tympani;  in  the  small  petrosal,  and  in  the  nervi  erigentes. 

These  nerve-fibres,  as  far  as  we  know  at  present,  leave  the  central 
nervous  system  among  the  fine  medullated  nerves  of  the  cervico-cra- 
nial  and  sacral  rami  communicantes,  do  not  enter  the  lateral  ganglia, 
but  pass  without  losing  their  medulla  into  the  collateral  or  terminal  gan- 
glia. 

(b.)  i.  Viscero-motor  Fibres. — These  fibres,  upon  which  depend  the 
peristaltic  movements  of  the  thoracic  portion  of  the  oesophagus,  and  of 
the  stomach,  and  intestines,  arise  from  the  central  nervous  system,  as 
the  fine  medullated  fibres  of  the  upper  portion  of  the  cervical  region,  not 
in  the  spinal  nerve  roots  of  that  region,  but  as  the  bundles  of  fibres 
which  may  be  called  the  rami  viscerales  of  the  vagus  and  accessory  nerves. 
They  pass  to.  the  ganglion  of  the  trunk  of  the  vagus,  where  they  lose 
their  medulla. 

ii.  Viscero- Inhibitory  Fibres. — It  appears  that  the  nerve- supply  to 
the  circular  muscles  of  the  alimentary  canal  and  its  appendages  is  con- 
tained in  the  abdominal  splanchnics,  and  consists  of  those  fibres  which 


THE   SYMPATHETIC    NERVOUS    SYSTEM.  629 

have  not  passed  through  the  lateral  chain,  and  which  therefore  retain 
their  medulla  until  they  reach  the  proximal  or  collateral  chain. 

c.  Glandular  Nerve  Fibres. — A  double  nerve  supply,  in  all  proba- 
bility coinciding  with  the  supply  to  the  visceral  muscles,  has  been 
demonstrated  in  the  cases  of  the  submaxillary,  parotid,  and  lachrymal 
glands,  and  in  these  cases  the  course  of  the  fibres  is  very  similar  to  that 
of  the  corresponding  fibres  for  the  vaso-muscular  supply.  Thus  the 
sympathetic  supply  for  these  glands  passes  along  with  the  vaso-motor 
fibres  from  the  cervical  splanchnic  (or  sympathetic  trunk),  and  superior 
cervical  ganglion;  whilst  the  cerebro-spinal  supply  comes  from  the  rami 
viscerales  of  the  cranial  nerves  in  conjunction  with  the  vaso-dilator 
fibres. 

Central  Origin  of  the  Rami  Viscerales. — There  appears  to  be  the 
strongest  presumption  that  the  white  rami  of  the  thoracic  region  arise  in 
the  spinal  cord  in,  or  are  connected  with,  the  cells  of  the  posterior  vesic- 
ular column  of  Clarke.  This  conclusion  is  based  upon  the  fact  that 
these  special  cells  are  found  in  the  three  regions  already  mentioned,  and 
in  those  only  where  the  white  rami  of  fine  medullated  fibres  exist,  viz., 
in  the  cervico-cranial  regions,  in  the  spinal  accessory,  in  the  thoracic 
region,  and  in  the  sacral  region.  But  it  is  probable  that  the  fibres  are 
also  connected  with  the  cells  of  the  lateral  horn  of  the  gray  matter  of  the 
spinal  cord,  and  its  representative  in  the  medulla,  the  antero-lateral 
nucleus  of  Clarke. 

B.  Structure  and  Functions  of  the  Ganglia. — The  sympathetic 
ganglia  all  contain — (1.)  nerve-fibres  traversing  them;  (2.)  nerve-fibres 
■originating  in  them;  (3.)  nerve-  or  ganglion-corpuscles,  giving  origin  to 
these  fibres;  and  (4.)  other  corpuscles  that  appear  free.  In  the  sympa- 
thetic ganglia  of  the  frog,  ganglion-cells  of  a  very  complicated  structure 
have  been  described  by  Beale,  and  subsequently  by  Arnold.  The  cells 
are  inclosed  each  in  a  nucleated  capsule:  they  are  pyriformin  shape,  and 
from  the  pointed  end  two  fibres  are  given  off,  which  gradually  acquire 
the  characters  of  nerve-fibres:  one  of  them  is  straight,  and  the  other 
(which  sometimes  arises  from  the  cell  by  two  roots)  is  spirally  coiled 
around  it. 

According  to  Gaskell  the  functions  of  the  main  sympathetic  ganglia 
are  the  following: — (1.)  They  effect  the  conversion  of  medullated  into 
non-medullated  fibres;  (2.)  They  possess  a  nutritive  influence  over  the 
nerves  which  pass  from  them  to  the  periphery;  (3.)  They  increase  the 
number  of  fibres  at  the  same  time  as  they  cause  the  removal  of  the 
medulla.  As  regards  their  possession  of  the  usual  properties  of  nerve- 
centres  little  or  nothing  is  certainly  known.  It  appears  unlikely  that 
they  possess  the  reflex  functions  of  the  spinal  centres. 

^Respecting  the  general  action  of  the  peripheral  ganglia  of  the  sympa- 
thetic, in  reflex  or  other  actions,  little  need  be  said,  since  they  may  be 


630  HANDBOOK    OF   PHYSIOLOGY. 

taken  as  examples  by  which  to  illustrate  the  common  modes  of  action  of 
all  nerve-centres.  Indeed,  complex  as  the  sympathetic  system,  taken  as 
a  whole,  is,  it  presents  in  each  of  its  parts  a  simplicity  not  to  be  found 
in  the  cerebro-spinal  system:  for  each  ganglion  with  afferent  and  efferent 
nerves  forms  a  simple  nervous  system,  and  might  serve  for  the  illustra- 
tion of  all  the  nervous  actions  with  which  the  cerebrum  is  unconnected. 

The  parts  principally  supplied  with  sympathetic  nerves  are  usually 
capable  of  none  but  involuntary  movements,  and  when  the  cerebrum 
acts  on  them  at  all,  it  is  only  through  the  strong  excitement  or  depress- 
ing influence  of  some  passion,  or  through  some  voluntary  movement  with 
which  the  actions  of  the  involuntary  part  are  commonly  associated. 
The  heart,  stomach,  and  intestines  are  examples  of  these  statements;  for 
the  heart  and  stomach,  though  supplied  in  large  measure  from  the 
pneumogastric  nerves,  yet  probably  derive  through  them  few  filaments 
except  such  as  have  arisen  from  their  ganglia,  and  are  therefore  of  the 
nature  of  sympathetic  fibres. 

The  parts  which  are  supplied  with  motor  power  by  the  sympathetic 
nerve  continue  to  move,  though  more  feebly  than  before,  when  they  are 
separated  from  their  natural  connections  with  the  rest  of  the  sympathetic 
system,  and  wholly  removed  from  the  body.  Thus,  the  heart,  after  it 
is  taken  from  the  body,  continues  to  beat  in  Mammalia  for  one  or  two 
minutes,  in  reptiles  and  Amphibia  for  hours;  and  the  peristaltic  motions 
of  the  intestine  continue  under  the  same  circumstances.  Hence  the 
motions  of  the  parts  supplied  with  nerves  from  the  sympathetic  are 
shown  to  be,  in  a  measure,  independent  of  the  brain  and  spinal  cord; 
this  independent  maintenance  of  their  action  being,  without  doubt,  due 
to  the  fact  that  they  contain,  in  their  own  substance,  the  apparatus  of 
ganglia  and  nerve-fibres  by  which  their  motions  are  immediately  gov- 
erned. 

It  seems  to  be  a  general  rule,  at  least  in  animals  that  have  both  cere- 
bro-spinal and  sympathetic  nerves  much  developed,  that  the  involuntary 
movements  excited  by  stimuli  conveyed  through  ganglia  are  orderly  and 
like  natural  movements,  while  those  excited  through  nerves  without 
ganglia  are  convulsive  and  disorderly;  and  the  probability  is  that,  in  the 
natural  state,  it  is  through  the  same  ganglia  that  natural  stimuli,  im- 
pressing centripetal  nerves,  are  reflected  through  centrifugal  nerves  to 
the  involuntary  muscles.  As  the  muscles  of  respiration  are  maintained 
in  uniform  rhythmic  action  chiefly  by  the  reflecting  and  combining  power 
of  the  medulla  oblongata,  so  are  those  of  the  heart,  stomach,  and  intes- 
tines, by  their  several  ganglia.  And  as  with  the  ganglia  of  the  sympa- 
thetic and  their  nerves,  so  with  the  medulla  oblongata  and  its  nerves 
distributed  to  the  respiratory  muscles — if  these  nerves  of  the  medulla 
oblongata  itself  be  directly  stimulated,  the  movements  that  follow  are 
convulsive  and  disorderly;  but  if  the  medulla  be  stimulated  through  a 


THE    SYMPATHETIC    NERVOUS    SYSTEM.  031 

centripetal  nerve,  as  when  cold  is  applied  to  the  skin,  then  the  impres- 
sions are  reflected  so  as  to  produce  movements  which,  though  they  may 
be  very  quick  and  almost  convulsive,  are  yet  combined  in  the  plan  of  the 
proper  respiratory  acts. 

Among  the  ganglia  of  the  sympathetic  nerves  to  which  this  co-ordi- 
nation of  movements  is  to  be  ascribed,  must  be  reckoned  those  which  lie 
in  the  very  substance  of  the  organs;  such  as  those  of  the  heart.  Those 
also  may  be  included  which  have  been  found  in  the  mesentery  close  by 
the  intestines,  as  well  as  in  the  muscular  aud  submucous  tissue  of  the 
stomach  and  intestinal  canal,  and  in  other  parts. 

Respecting  the  influence  of  the  sympathetic  system  on  the  various 
physiological  processes,  the  sections  on  the  Heart,  Arteries,  Animal 
Heat,  Salivary  Glands,  StomacH  and  Intestines  should  be  referred  to. 

Influence  of  the  Nervous  System  in  general  on  Nutrition. — It 
has  been  held  that  the  nervous  system  cannot  be  essential  to  a  healthy 
course  of  nutrition,  because  in  plants,  in  the  early  embryo,  and  in  the 
lowest  animals,  in  which  no  nervous  system  is  developed,  nutrition  goes 
on  without  it.  But  this  is  no  proof  that  in  animals  which  have  a  ner- 
vous system,  nutrition  may  be  independent  of  it;  rather,  it  may  be 
assumed,  that  in  ascending  development,  as  one  system  after  another  is 
added  or  increased,  so  the  highest  (and,  highest  of  all,  the  nervous  sys- 
tem) will  always  be  present  and  blended  in  a  more  and  more  intimate 
relation  with  all  the  rest:  according  to  the  general  law,  that  the  inter- 
dependence of  parts  augments  with  their  development. 

The  reasonableness  of  this  assumption  is  proved  by  many  facts  show- 
ing the  influence  of  the  nervous  system  on  nutrition,  and  by  the  most 
striking  of  these  facts  heing  observed  in  the  higher  animals,  and  espe- 
cially in  man.  The  influence  of  the  mind  in  the  production,  aggravation, 
and  cure  of  organic  diseases  is  matter  of  daily  observation,  and  a  sufficient 
proof  of  influence  exercised  on  nutrition  through  the  nervous  system. 

Independently  of  mental  influence,  injuries  either  to  portions  of  the 
nervous  centres,  or  to  individual  nerves,  are  frequently  followed  by 
defective  nutrition  of  the  parts  supplied  by  the  injured  nerves,  or  deriv- 
ing their  nervous  influence  from  the  damaged  portions  of  the  nervous 
centres.  Thus,  lesions  of  the  spinal  cord  are  sometimes  quickly  followed 
by  gangrene  of  portions  of  the  paralyzed  parts.  After  such  lesions  also,. 
the  repair  of  injuries  in  the  paralyzed  parts  may  take  place  less  com- 
pletely than  in  others;  as,  in  a  case  in  which  paraplegia  was  produced 
by  fracture  of  the  lumbar  vertebra?,  and,  in  the  same  accident,  the 
humerus  and  tibia  were  fractured.  The  former  in  due  time  united:  the 
latter  did  not.  The  same  fact  was  illustrated  by  some  experiments,  in 
which  having,  in  salamanders,  cut  off  the  end  of  the  tail,  and  then 
thrust  a  thin  wire  some  distance  up  the  spinal  canal,  so  as  to  destroy  the 
cord,  it  was  found  that  the  end  of  the  tail  was  reproduced  more  slowly 


t>32  HANDBOOK    OF    PHYSIOLOGY. 

than  in  other  salamanders  in  whom  the  spinal  cord  was  left  uninjured 
above  the  point  at  which  the  tail  was  amputated.  Illustrations  of  the 
same  kind  are  furnished  by  the  several  cases  in  which  division  or  de- 
struction of  the  trunk  of  the  trigeminal  nerve  has  been  followed  by 
incomplete  and  morbid  nutrition  of  the  corresponding  side  of  the  face; 
ulceration  of  the  cornea  being  often  directly  or  indirectly  one  of  the 
consequences  of  such  imperfect  nutrition.  Part  of  the  wasting  and  slow 
degeneration  of  tissue  in  paralyzed  limbs  is  probably  referable  also  to  the 
withdrawal  of  nervous  influence  from  them;  though,  perhaps,  more  is 
due  to  the  want  of  use  of  the  tissues. 

Undue  irritation  of  the  trunks  of  nerves,  as  well  as  their  division  or 
destruction,  is  sometimes  followed  by  defective  or  morbid  nutrition.  To 
this  may  be  referred  the  cases  in  which  ulceration  of  the  parts  supplied 
by  the  irritated  nerves  occurs  frequently,  and  continues  so  long  as  the 
irritation  lasts. 

So  many  and  varied  facts  leave  little  doubt  that  the  nervous  system 
exercises  an  influence  over  nutrition  as  over  other  organic  processes;  and 
they  cannot  be  easily  explained  by  supposing  that  the  changes  in  the 
nutritive  processes  are  only  due  to  the  variations  in  the  size  of  the  blood- 
vessels supplying  the  affected  parts,  although  this  is,  doubtless,  one  im- 
portant element  in  producing  the  result. 

As  a  contribution  towards  the  explanation  of  the  nervous  mechanism 
of  nutrition  comes  in  GaskelFs  theory  of  katabolic  and  anabolic  nerves. 
He  supposes  that  every  tissue  is  supplied  with  two  sets  of  nerves,  the 
former  of  which  corresponds  with  the  motor  nerve,  the  viscero-motor, 
and  the  cardio-augmentor,  by  the  stimulation  of  which  an  increase  of  the 
metabolism  takes  place,  and  which  is  followed  by  exhaustion.  It  may 
be  accompanied  either  by  contraction  of  a  muscle  or  by  an  increase  of 
contraction.  Such  a  nerve  is  excellently  illustrated  by  the  sympathetic 
augmentor  or  accelerator  nerve  of  the  heart,  on  stimulation  of  which  an 
increase  in  the  force  and  frequency  of  the  heart  takes  place,  followed 
after  a  time  by  exhaustion.  A  katabolic  nerve  stimulates  the  destructive 
metabolism  which  is  always  going  on  in  a  tissue.  The  anabolic  nerve  is 
the  exact  opposite  of  the  katabolic  nerve  in  function.  It  subserves  con- 
structive metabolism.  Stimulation  of  the  nerve  produces  diminished 
activity,  repair  of  tissue,  and  building  up.  An  example  of  this  kind  of 
nerve  is  seen  in  the  cardiac  vagus,  stimulation  of  which  produces 
inhibition.  Inhibition  must  generally  be  looked  upon  as  an  anabolic 
process. 

It  will  be  seen  that  the  results  of  stimulation  of  the  nerves  to  the 
salivary  glands,  discussed  in  a  former  chapter,  appear  to  support  the 
theory  that  the  processes  of  constructive  and  destructive  metabolism  are 
under  the  control  of  separate  nerve  fibres.  In  the  case  of  the  submaxil- 
lary gland,  for  example,  if  the  sympathetic  fibres  be  stimulated,  a  kata- 


THE    SYMPATHETIC    NEKV0U8    SYSTEM.  633 

bolic  effect  is  produced,  and  the  materials  of  secretion  are  formed  at  the 
expense  of  the  protoplasm  (this  action  in  the  case  of  the  gland  Heiden- 
hain  calls  trophic) ;  if  on  the  other  hand  the  chorda  tympani  or  the 
secretory  nerve  be  stimulated,  two  things  happen,  one  being  the  discharge 
of  water  and  the  materials  of  secretion  from  the  gland  cells,  and  the 
other  the  building  up  or  reconstruction  of  the  protoplasm  of  the  cells. 
A  part  of  this  action  at  any  rate  is  anabolic,  and  similar  to  the  action  of 
inhibitory  nerves. 


CHAPTEE   XXII. 


THE  REPRODUCTIVE   ORGANS. 


Before  describing  the  method  of  Eeproduction  or  the  way  in  which 
the  species  is  propagated,  it  will  be  advisable  to  describe  the  structure 
of  those  organs  which  in  either  sex  are  concerned  in  reproduction,  and 


Fig.  424.— Diagrammatic  view  of  the  uterus  and  its  appendages,  as  seen  from  behind.  The 
uterus  and  the  upper  part  of  the  vagina  have  been  laid  open  by  removing  the  posterior  wall;  the 
Fallopian  tube,  round  ligament,  and  ovarian  ligament  have  been  cut  short,  and  the  broad  ligament 
removed  on  the  left  side;  it,  the  upper  part  of  the  uterus;  c,  the  cervix  opposite  the  os  internum; 
the  triangular  shape  of  the  uterine  cavity  is  shown,  and  the  dilatation  of  the  cervical  cavity  with 
the  rugae  termed  arbor  vitae;  v,  upper  part  of  the  vagina;  od,  Fallopian  tube  or  oviduct;  the  nar- 
row communication  of  its  cavity  with  that  of  the  cornu  of  the  uterus  on  each  size  is  seen ;  I,  round 
ligament;  lo,  ligament  of  the  ovary;  o,  ovary;  i,  wide  outer  part  of  the  right  Fallopian  tube:  fi,  its 
fimbriated  extremity;  po.  parovarium;  7i,  one  of  the  hydatids  frequently  found  connected  with  the 
broad  ligament.    %.    (Allen  Thomson.") 

which  are  called  the  genital  or  generative  organs  or  the  sexual  appa- 
ratus. 

A.     The  Genital  Organs  of  the  Female. 

The  female  organs  of  generation  (Fig.  424)  consist  of  two  Ovaries, 
whose  function  is  the  formation  of  ova;  of  a  Fallopian  tube,  or  oviduct, 
connected  with  each  ovary,  for  the  purpose  of  conducting  the  ovum  from 
the  ovary  to  the  Uterus  or  cavity  in  which,  if  impregnated,  it  is  retained 
until  the  embryo  is  fully  developed,  and  fitted  to  maintain  its  existence 
independently  of  internal  connection  with  the  parent;  and,  lastly,  of  a 
canal,  or  vagina,  with  its  appendages,  for  the  reception  of  the  male  or- 


THE    REPRODUCTIVE    ORGANS. 


635 


gan  in  the  act  of  copulation,  and  for  the  subsequent  discharge  of  the 
foetus. 

a.  The   Ovaries. — The    ovaries  are  two    oval  compressed  bodies,. 


Fig.  425.— View  of  a  section  of  the  ovary  of  the  cat.  1,  outer  covering  and  free  border  of  the 
ovary;  1',  attached  border;  U,  the  ovarian  stroma,  presenting  a  fibrous  and  vascular  structure;  3, 
granular  substance  lying  external  to  the  fibrous  stroma;  4,  blood- vessels;  5,  ovigerms  in  their  earli- 
est stages  occupying  a  part  of  the  granular  layer  near  the  surface;  6.  ovigerms  which  have  begun 
to  enlarge  and  to  pass  more  deeply  into  the  ovary;  7,  ovigerms  round  which  the  Graafian  follicle 
and  tunica  granulosa  are  now  formed,  and  which  have  passed  somewhat  deeper  into  the  ovary  and 
are  surrounded  by  the  fibrous  stroma;  8.  more  advanced  Graafian  follicle  with  the  ovum  imbedded 
in  the  layer  of  the  cells  constituting  the  proligerous  disc;  9,  the  most  advanced  follicle  containing 
the  ovum,  etc.;  9',  a  follicle  from  which  the  ovum  has  accidentally  escaped;  10,  corpus  luteum.  G  1. 
(SchronO 

situated  in  the  cavity  of  the  pelvis,  one  on  each  side,  enclosed  in  the 
folds  of  the  broad  ligament.     Each  ovary  measures  about  an  inch  and  a 


Fig.  426.— Section  of  the  ovary  of  a  cat.  A,  germinal  epithelium;  B.  immature  Graafian  follicle; 
C.  stroma  of  ovary;  I).  vitelline  membrane  containing  the  ovum;  E,  Graafian  follicle  showing  lining 
cells;  F,  follicle  from  which  the  ovum  has  fallen  out.    (V.  D.  Harris.  > 


half  in  length,  three-quarters  of  an  inch   in  width,  and  nearly  half  an 
inch  in  thickness,  and  is.  attached  to  the  uterus  by  a  narrow  fibrous  cord 


636  HANDBOOK    OF    PHYSIOLOGY. 

(the  ligament  of  the  ovary),  and,  more  slightly,  to  the  Fallopian  tubes 
by  one  of  the  fimbria?  into  which  the  walls  of  the  extremity  of  the  tube 
expand. 

Structure. — The  ovary  is  enveloped  by  a  capsule  of  dense  fibro-cellu- 
lar  tissue,  called  the  tunica  albuginea,  covered  on  the  outside  by  epithe- 
lium (germ-epithelium),  the  cells  of  which,  although  continuous  with, 
and  originally  derived  from,  the  squamous  epithelium  of  the  peritoneum, 
are  short  columnar  (A,  Fig.  426). 

The  internal  structure  of  the  organ  consists  of  a  peculiar  soft  fibrous 
tissue — a  kind  of  undeveloped  connective  tissue,  with  long  nuclei  closely 
resembling,  unstriped  muscle  (C,  Fig.  426) — or  stroma,  abundantly  sup- 
plied with  blood-vessels,  and  having  imbedded  in  it,  in  various  stages  of 
development,  numerous  minute  follicles  or  vesicles,  the  Graafian  vesi- 
cles, or  sacculi,  containing  the  ova  (Fig.  426). 

If  the  ovary  be  examined  at  any  period  between  early  infancy  and  ad- 
vanced age,  but  especially  during  that  period  of  life  in  which  the  power 
of  conception  exists,  it  will  be  found  to  contain  a  number  of  these  vesi- 
cles. Immediately  under  the  tunica  albuginea  (Fig.  426)  they  are  small 
and  numerous,  either  arranged  as  a  continuous  layer,  as  in  the  cat  or 
rabbit,  or  in  groups,  as  in  the  human  ovary.  These  small  follicles  im- 
bedded in  the  soft  stroma  of  fine  connective  tissue  and  unstriped  muscle 
form  here  the  cortical  layer;  they  are  sometimes  called  ovisacs, 

Each  of  the  small  follicles  of  this  layer  has  an  external  membranous 
envelope,  or  membrana  propria.  This  envelope  or  tunic  is  lined  with  a 
layer  of  nucleated  cells,  forming  a  kind  of  epithelium  or  internal  tunic, 
and  named  the  membrana  granulosa.  The  cavity  of  the  follicle  is  filled 
up  by  a  nucleated  mass  of  protoplasm  enclosed  in  a  very  delicate  mem- 
brane, which  is  the  Ovum.  The  nucleus  contains  one  or  more  nucleoli. 
The  nucleus  is  known  as  the  germinal  vesicle,  and  the  nucleolus  as  the 
germinal  spot. 

The  central  portion  of  the  stroma  of  the  ovary  extends  from  the  cor- 
tical layer  to  the  hilum  of  the  organ,  at  which  enter  the  numerous  arte- 
ries, fibrous  tissue,  and  unstriped  muscle,  forming  a  highly  vascular 
zona  vasculosa.  Within  this  central  zone  are  contained  the  fully-devel- 
oped Graafian  follicles,  varying  in  size,  however,  but  considerably  larger 
than  those  of  the  cortical  layer.  In  these  follicles  the  cavity  is  not  nearly 
filled  by  the  ovum,  which  is  attached  at  one  side  to  the  zona  granulosa 
by  a  collection  of  small  cells,  the  discus proligerus,  the  remainder  of  the 
cavity  being  filled  with  fluid.  The  envelope  of  the  ovum,  or  zona  pellu- 
cida,  is  much  thicker.  The  zona  granulosa  is  formed  of  several  layers 
of  cells,  instead  of  one  only.  Its  membrana  propria  is  much  thicker,  so 
as  to  form  a  distinct  fibrous  investment;  the  membrana  fibrosa  and  the 
blood-vessels  surrounding  it  are  numerous,  and  may  be  said  to  form  a 
membrana  vasculosa  about  it. 


THE  REPRODUCTIVE  ORGANS.  637 

The  human  ovum  measures  about  j^oi  an  inch.  Its  external  invest- 
ment, or  the  zona  pellucida,  or  vitelline  membrane,  is  a  transparent 
membrane,  about  y^uts  °^  an  in°h  *n  thickness,  which  under  the  micro- 
scope appears  as  a  bright  ring  (4,  Fig.  427),  bounded  externally  and  in- 
ternally by  a  dark  outline.  Within  this  transparent  investment  or  zona 
pellucida,  and  usually  in  close  contact  with  it,  lies  the  yolk  or  vitellus, 
which  is  composed  of  granules  and  globules  of  various  sizes,  imbedded 
in  a  more  or  less  fluid  substance.  The  smaller  granules,  which  are  the 
more  numerous,  resemble  in  their  appearance,  as  well  as  their  constant 
motion,  pigment-granules.  The  larger  granules  or  globules,  which  have 
the  aspect  of  fat-globules,  are  in  greatest  number  at  the  periphery  of  the 
yolk.  The  number  of  the  granules  is  greatest  in  the  ova  of  carnivorous 
animals.     In  the  human  ovum  their  quantity  is  comparatively  small. 

In  the  substance  of  the  yolk  is  imbedded  the  germinal  vesicle,  or 
vesicula  germinativa  (2,  Fig.  427).  The  vesicle  is  of  greatest  relative 
size  in  the  smallest  ova,  and  is  in  them  surrounded  closely  by  the  yolk, 
nearly  in  the  centre  of  which  it  lies.  During  the  development  of  the 
ovum,  the  germinal  vesicle  increases  in  size  much  less  rapidly  than  the 
yolk,  and  comes  to  be  placed  near  to  its  surface.  It  consists  of  a  fine, 
transparent,  structureless  membrane,  containing  a  clear,  watery  fluid,  in 
which  are  sometimes  a  few  granules;  and  at  that  part  of  the  periphery  of 
the  germinal  vesicle  which  is  nearest  to  the  periphery  of  the  yolk  is  situ- 
ated the  germinal  spot,  or  macula  germinativa,  of  a  finely  granulated  ap- 
pearance and  of  a  yellowish  color,  strongly  refracting  the  rays  of  light. 

Such  are  the  parts  of  which  the  Graafian  follicle  and  its  contents, 
including  the  ovum,  are  composed.  With  regard  to  the  mode  and  order 
of  development  of  these  parts  there  is  considerable  uncertainty. 

It  appears  that  the  Graafian  follicles  are  formed  in  the  following 
manner: — The  embryonic  ovary  is  covered  with  short  columnar  cells,  or 
the  so-called  germinal  epithelium.  The  cells  of  this  layer  undergo  pro- 
liferation, so  as  to  form  several  strata.  These  cells  grow  into  the  ovarian 
stroma  as  longer  or  shorter  columns  or  tubes.  By  degrees  these  tubes 
become  cut  off  from  the  surface  epithelium,  and  form  cell  nests,  small  if 
near  the  surface,  larger  if  in  the  depth  of  the  stroma.  The  nests  in- 
crease in  size  from  multiplication  of  their  cells,  and  may  even  give  off 
new  nests  laterally  by  constriction  of  them  in  various  directions.  Certain 
of  the  cells  of  the  germinal  epithelium  enlarge,  and  form  ova;  and  the 
formation  of  ova  also  takes  place  in  the  nests  within  the  stroma.  The 
ova  of  a  nest  may  multiply  by  division.  The  small  cells  of  a  nest  sur- 
round the  ova,  and  form  their  membrana  granulosa,  and  the  stroma 
growing  up  separates  the  surrounded  ova  into  so  many  Graafian  follicles. 
The  other  layers,  namely,  the  membrana  fibrosa  and  the  membrana 
vasculosa,  are  derived  from  the  stroma. 

The  smallest  follicles  are  formed  at  the  surface,  and  form  the  cortical 


■638 


HANDBOOK    OF    PHYSIOLOGY. 


layer.  It  is  said  by  some  that  the  superficial  follicles  as  they  ripen  be- 
come more  deeply  placed  in  the  ovarian  stroma;  and,  again,  that  as  they 
increase  in  size,  they  make  their  way  towards  the  surface  (Fig.  425). 

When  mature,  they  form  little  prominences  on  the  exterior  of  the 
ovary,  covered  only  by  a  thin  layer  of  condensed  fibrous  tissue  and  epi- 
thelium.    Only  a  few  follicles  ever  reach  maturity. 

From  the  earliest  infancy,  and  through  the  whole  fruitful  period  of 
life,  there  appears  to  be  a  constant  formation,  development,  and  matura- 
tion of  Graafian  vesicles,  with  their  contained  ova.  Until  the  period  of 
puberty,  however,  the  process  is  comparatively  inactive;  for,  previous  to 
this  pe^'od,  the  ovaries  are  small  and  pale,  the  Graafian  vesicles  in  them 
are  very  minute,  and  probably  never  attain  full  development,  but  soon 
shrivel  and  disappear,  instead  of  bursting,  as  matured  follicles  do;  the 
contained  ova  are  also  incapable  of  being  impregnated.  But,  coincident 
with  the  other  changes  which  occur  in  the  body  at  the  time  of  puberty, 
the  ovaries  enlarge,  and  become  very  vascular,  the  formation  of  Graafian 


wme§f 


Fig.  428. 

Fig.  427.— Ovum  of  the  sow.  1,  germinal  spot;  2,  germinal  vesicle;  3,  yolk;  4,  zona  pellucida; 
5,  discus  proligerus;  6,  adherent  granules  or  cells.    (Barry.) 

Fig.  428.  —Germinal  epithelium  of  the  surface  of  the  ovary  of  five  days'  chick,  a,  small  ovo- 
blasts;  b,  larger  ovoblasts.    (Cadiat.) 

vesicles  is  more  abundant,  the  size  and  degree  of  development  attained 
by  them  are  greater,  and  the  ova  are  capable  of  being  fecundated. 

i.  The  Fallopian  Tubes  or  Oviducts. — The  Fallopian  tubes  are 
about  four  inches  in  length,  and  extend  between  the  ovaries  and  the 
upper  angles  of  the  uterus.  At  the  point  of  attachment  to  the  uterus, 
the  tube  is  very  narrow;  but  in  its  course  to  the  ovary  it  increases  to 
about  a  line  and  a  half  in  thickness;  at  its  distal  extremity,  which  is 
free  and  floating,  it  bears  a  number  of  fimbrice,  one  of  which,  longer  than 
the  rest,  is  attached  to  the  ovary.  The  canal  by  which  each  tube  is  tra- 
versed is  narrow,  especially  at  its  point  of  entrance  into  the  uterus,  at 
which  it  will  scarcely  admit  a  bristle;  its  other  extremity  is  wider,  and 
opens  into  the  cavity  of  the  abdomen,  surrounded  by  the  zone  of  fim- 
briae. Externally,  the  Fallopian  tube  is  invested  with  peritoneum;  in- 
ternally, its  canal  is  lined  with  mucus  membrane,  which  is  apt  to  be 
thrown  into  numerous  folds,  covered  with  ciliated  epithelium:  between 
the  peritoneal  and  mucous  coats,  the  walls  are  composed,  like  those  of 


THE    REPRODUCTIVE    SYSTEM.  639 

the  uterus,  of  fibrous  tissue  and  unstriped  muscular  fibres,  chiefly  circu- 
lar in  arrangement. 

c.  The  Uterus. — The  Uterus  (u,  c,  Fig.  424)  is  somewhat  pyriform, 
and  in  the  unimpregnated  state  is  about  three  inches  in  length,  two  in 
breadth  at  its  upper  part  or  fundus,  but  at  its  lower  pointed  part  or 
neck,  only  about  half  an  inch.  The  part  between  the  fundus  and  neck 
is  termed  the  body  of  the  uterus:  it  is  about  an  inch  in  thickness. 

Structure. — The  uterus  is  constructed  of  three  principal  layers,  or 
coats — serous,  fibrous  Audi  muscular,  and  mucous.  (1.)  The  serous  coat, 
which  has  the  same  general  structure  as  the  peritoneum,  covers  the 
organ  before  and  behind,  but  is  absent  from  the  front  surface  of  the 
neck.  (2.)  The  middle  coat  is  composed  of  unstriped  muscle,  arranged 
in  the  human  uterus  in  three  layers  from  without  inwards,  longitu- 
dinal, circular,  oblique  and  circular.  They  become  enormously  devel- 
oped during  pregnancy.  The  arteries  and  veins  are  found  in  large 
numbers  in  the  outer  part  of  this  coat,  so  as  to  form  almost  a  special 
vascular  covering.  (3.)  The  mucous  membrane  of  the  uterus  is  lined 
by  columnar  ciliated  epithelium,  which  extends  also  into  the  interior  of 
the  tubular  glands,  of  which  the  mucous  membrane  is  largely  made  up. 

In  the  neck  of  the  uterus  (cervix)  the  mucous  membrane  is  arranged 
in  permanent  longitudinal  folds,  palmar  plicatae,  and  between  these  folds 
open  the  ducts  of  the  tubular  glands.  In  the  fundus  the  proper  tissue 
is  a  spongy  tissue  of  interlacing  fibrous  bundles,  forming  a  system  of 
lymph  channels.  Here  the  lining  is  a  single  layer  of  flattened  cells. 
The  tubular  glands  are  usually  simple  and  unbranched,  and  seldom  wavy 
or  convoluted. 

The  cavity  of  the  uterus  corresponds  in  form  to  that  of  the  organ 
itself:  it  is  very  small  in  the  unimpregnated  state;  the  sides  of  its  mu- 
cous surface  being  almost  in  contact.  Into  its  upper  part,  at  each  side, 
opens  the  canal  of  the  corresponding  Fallopian  tube:  below,  it  commu- 
nicates with  the  vagina  by  a  fissure  like  opening  in  its  neck,  the  os  uteri, 
the  margins  of  which  are  distinguished  into  two  lips,  an  anterior  and 
posterior.  In  the  mucous  membrane  of  the  cervix  are  found  several 
mucous  follicles,  termed  ovulaor  glandular  Nabothi:  they  probably  form 
the  jelly-like  substance  by  which  the  os  uteri  is  usually  found  closed. 

The  vagina  is  a  membranous  canal,  five  or  six  inches  long,  extend- 
ing obliquely  downwards  and  forwards  from  the  neck  of  the  uterus, 
which  itembraces,  to  the  external  organs  of  generation.  It  is  lined  with 
mucous  membrane,  covered  with  stratified  squamous  epithelium,  which 
in  the  ordinary  contracted  state  of  the  canal  is  thrown  into  transverse 
folds.  External  to  the  mucous  membrane  the  walls  of  the  vagina  are 
constructed  of  unstriped  muscle  and  fibrous  tissue,  within  which  in  the 
submucosa,  especially  around  the  lower  part  of  the  tube,  is  a  layer  of 
erectile  tissue.     This  exists  also  in  the  mucosa.     The  lower  extremity  of 


640  HANDBOOK    OF    PHYSIOLOGY. 

the  vagina  is  embraced  by  an  orbicular  muscle,  the  constrictor  vagina? 
its  external  orifice,  in  the  virgin,  is  partially  closed  by  a  fold  or  ring  of 
mucous  membrane,  termed  the  hymen.  The  external  organs  of  genera- 
tion consist  of  the  clitoris,  a  small  elongated  body,  situated  above  and 
in  the  middle  line,  and  constructed  of  two  erectile  masses  or  corpora 
cavernosa.  They  are  not  perforated  by  the  urethra;  of  two  folds  of  mu 
cous  membrane,  termed  labia  interna  ox  nymplm;  and,  in  front  of  these, 
of  two  other  folds,  the  labia  externa,  or  pudenda,  formed  of  the  external 
integument,  and  lined  internally  by  mucous  membrane.  Between  the 
nymphse  and  beneath  the  clitoris  is  an  angular  space,  termed  the  vesti- 
bule, at  the  centre  of  whose  base  is  the  orifice  of  the  meatus  urinarius. 
Numerous  mucous  follicles  are  scattered  beneath  the  mucous  membrane 
composing  these  parts  of  the  external  organs  of  generation;  and  at  the 
side  of  the  lower  part  of  the  vagina  are  two  larger  lobulated  glands, 
vulvo-vaginal  or  Duverney's  glands,  which  are  analogous  to  Cowper's 
glands  in  the  male. 

B.  The  Genital  Organs  of  the  Male. 

The  male  organs  of  generation  comprise  the  two  Testes,  in  which 
the  semen  is  formed;  each  with  its  duct,  the  Vas  Deferens,  with  the 
accessory  Vesicula  Seminalis ;  and  the  Penis,  an  erectile  organ, 
through  which  the  semen  as  well  as  the  urine  is  discharged.  The  Pros- 
tate gland,  the  exact  function  of  which  is  not  understood,  is  generally 
included  in  the  same  class. 

a.  The  Testes. — The  secreting  structure  of  the  testicle  and  its  duct 
are  disposed  of  in  two  contiguous  parts,  (1)  the  body  of  the  testicle 
proper,  inclosed  within  a  thick  and  tough  white  fibrous  membrane,  the 
tunica  albuginea,  on  the  outer  surface  of  which  is  the  serous  covering 
formed  by  the  tunica  vaginalis,  aud  (2)  the  epididymis  and  vas  deferens. 

The  Vas  deferens,  or  duct  of  the  testicle,  which  is  about  two  feet  in 
length,  is  constructed  externally  of  connective  tissue,  and  internally  is 
lined  by  a  mucous  membrane,  covered  with  columnar  epithelium;  while 
between  these  two  coats  is  a  middle  coat,  very  firm  and  tough,  made  up 
of  unstriped  muscle,  chiefly  arranged  longitudinally,  but  also  containing 
some  circular  fibres.  When  followed  back  to  its  origin,  the  vas  deferens 
is  found  to  pass  to  the  lower  part  of  the  epididymis,  with  which  it  is 
directly  continuous  (Fig.  429),  and  assumes  there  a  much  smaller  diam- 
eter with  an  exceedingly  tortuous  course. 

The  Epididymis,  which  is  lined,  except  at  its  lowest  part,  by  colum- 
nar ciliated  epithelium  (Fig.  429),  is  commonly  described  as  consisting 
(Fig.  429)  of  &  globus  minor  (g),  the  body  (e),  and  the  globus  major  (I). 
When  unravelled,  it  is  found  to  be  constructed  of  a  single  tube,  measur- 
ing about  twenty  feet  in  length. 

At  the  globus  major  this  duct   divides  into    ten   or  twelve   small 


THE    REPROnrCTIVK    SYSTEM. 


641 


branches,  the  convolutions  of  which  form  coniform  masses,  named  Coni 
vasculosi;  and  the  ducts  continued  from  these,  the  Vasa  effcrentia,  after 
anastomosing,  one  with  another  in  what  is  called  the  Rete  testis,  lead 
fiually  as  the  Tubuli  recti  or  Vasa  recta  to  the  seminal  tubules,  or  form 
the  proper  substance  of  the  testicle.  The  epithelium  lining  the  coni 
vasculosi  and  vasa  effereutia  is  columnar  and  ciliated;  that  of  the  rete 
testis  is  squamous. 

The  seminal  tubules  are  arranged  in  lobules,  separated  from  one 
another  by  incomplete  fibrous  septa  or  cords,  which  pass  from  the  front 
of  the  tunica  albuginea  internally  to  a  firm  incomplete  vertical  septum 
of  thick  extending  fibrous  tissue  at  the  posterior  border,  from  the  upper 


Fig.  429. 


Fig.  430. 


Fig.  429.— Plan  of  a  vertical  section  of  the  testicle,  showing  the  arrangements  of  the  ducts. 
The  true  length  and  diameter  of  the  ducts  have  been  disregarded,  a.  a.  tubuli  seminiferi  coiled  up 
in  the  separate  lobes;  6,  tubuli  recti  or  vasa  recta:  c,  rete  testis;  d,  vasa  efferentia  ending  in  the 
coni  vasculosi;  I,  e,  a,  convoluted  canal  of  the  epididymis;  h,  vas  deferens;  /,  section  of  tne  back 
part  of  the  tunica  albuginea;  ?',  i,  fibrous  processes  running  between  the  lobes;  s.  mediastinum. 

Fig.  430.— Section  of  the  epididymis  of  a  dog.  The  tube  is  cut  in  several  places,  both  trans- 
versely and  obliquely;  it  is  seen  to  be  lined  by  a  ciliated  epithelium,  the  nuclei  of  which  are  well 
shown,    c,  connective  tissue.    (Schofield.) 


to  near  the  lower  part,  called  the  corpus  Highmori,  or  mediastinum  tes- 
tis. Through  this  very  firm  fibrous  tissue  pass  the  seminal  tubes  from 
the  vasa  recta.  The  tunica  albuginea  is  covered  by  a  very  fine  plexus  of 
blood-vessels  internally,  derived  from  the  spermatic  vessels.  The  fibrous 
cords  which  may  contain  unstriped  muscle  are  also  covered  with  a  simi- 
lar capillary  plexus. 

The  Seminal  Tubes. — The  seminal  tubes,  or  tubuli  seminiferi, 
•il 


642 


HANDBOOK    OF    PHYSIOLOGY. 


which  compose  the  parenchyma  of  the  testicle,  are  loosely  arranged  in 
lobules  between  the  connective-tissue  septa. 

They  are  relatively  large,  very  wavy,  and  much  convoluted;  and  they 
possess  a  few  lateral  branches,  by  which  they  become  connected  into  a  net- 
work. They  form  terminal  loops,  and  in  the  peripheral  portion  of  the 
testis  the  tubules  are  possessed  of  minute  lateral  caecal  branchlets. 

Each  seminal  tubule  in  the  adult  testis  is  limited  by  a  membrana 
propria,  which  appears  as  a  hyaline  elastic  membrane,  but  which  is 
really  made  up  of  several  incomplete  layers  of  flattened  cells,  containing 
oval  flattened  nuclei  at  regular  intervals.  Inside  this  membrana  propria 
are  several  layers  of  epithelial  cells,  the  seminal  cells.  These  consist  of 
two  or  more  layers,  the  outermost  being  situated  next  the  membrana 
propria.     These  cells  are  of  two  kinds,  those  that  are  in  a  resting  state, 


Fig.  431. 


432. 


Fig.  431.— A  section  of  a  dog's  testicle,  highly  magnified,  showing  three  "  tuhuli  seminiferi," 
lined  and  largely  occupied  by  a  spheroidal  epithelium,  the  numerous  nuclei  of  which  are  well  seen; 

c,  connective  tissue  surrounding  and  supporting  the  tubuli;  sp,  masses  of  spermatozoa  occupying 
the  centre  of  tubuli;  the  small  black  bodies  scattered  about  are  the  heads  of  the  spermatozoa. 
(Schofield.) 

Fig.  432.— Section  of  a  tubule  of  the  testicle  of  a  rat,  to  show  the  formation  of  the  spermatozoa, 
a,  spermatozoa;  b,  seminal  cells;  c,  spermatoblasts  to  which  the  spermatozoa  are  still  adherent; 

d,  membrana  propria;  e,  fibro-plastic  elements  of  the  connective  tissue.    (Cadiat.) 


which  generally  form  a  complete  layer,  and  those  that  are  in  a  state  of 
division,  of  which  there  may  be  two  layers.  The  latter  are  called  mother 
cells,  and  the  smaller  cells  resulting  from  their  division  are  called 
daughter  cells  or  spermatoblasts.  From  these  the  spermatozoa  are 
formed,  their  head  corresponding  with  the  nuclei  of  the  daughter  cells; 
and  during  their  development  they  lie  in  groups  (Fig.  432),  and  are  sup- 
ported by  irregular  masses  of  so-called  nutritive  cells;  but  when  fully 
formed,  they  become  detached,  and  fill  the  lumen  of  the  seminiferous 
tubule  (Fig.  431). 


THE    REPRODUCTIVE    SYSTEM.  643 

In  the  fine  connective  tissue  which  supports  the  tubules  of  the  testis 
are  to  be  found  flattened  and  nucleated  epithelial  cells,  probably  the  re- 
mains of  the  Wolffian  body.  The  lymphatics  of  the  testes  are  numerous, 
and  may  be  injected  by  inserting  the  needle  of  an  injecting  syringe  into 
the  tunica  albuginea,  and  pressing  in  the  injection  with  slight  effort. 

Vesiculae  Seminales. — The  vesiculce  seminales  have  the  appear- 
ance of  outgrowths  from  the  vasa  deferentia.  Each  vas  deferens,  just 
before  it  enters  the  prostate  gland,  through  part  of  which  it  passes  to 
terminate  in  the  urethra,  gives  off  a  side  branch,  which  bends  back  from 
it  at  an  acute  angle;  and  this  branch  dilating,  variously  branching,  and 
pursuing  in  both  itself  and  its  branches  a  tortuous  course,  forms  the 
vesicula  seminalis. 

Structure. — Each  of  the  vesiculae  may  be  unravelled  into  a  single 
branching  tube,  sacculated,  convoluted,  and  folded  up.  The  structure 
of  the  vesiculge  resembles  closely  that  of  the  vasa  deferentia.  The  mu- 
cous membrane  lining  the  vesicular  seminales,  like  that  of  the  gall-bladder, 


Fig.  433.— From  a  section  of  the  testis  of  dog,  showing  portions  of  seminal  tubes.  A,  seminal 
epithelial  cells,  and  numerous  small  cells  loosely  arranged;  B,  the  small  cells  or  spermatoblasts 
converted  into  spermatozoa;  C,  groups  of  these  in  a  further  stage  of  development.    (Klein.) 

is  minutely  wrinkled  and  set  with  folds  and  ridges  arranged  so  as  to  give 
it  a  finely  reticulated  appearance. 

The  Penis. — The  penis  is  composed  of  three  long  more  or  less 
cylindrical  masses,  inclosed  in  remarkably  firm  fibrous  sheaths,  of  which 
two,  the  corpora  cavernosa,  are  alike,  and  are  firmly  joined  together,  and 
receive  below  and  between  them  the  third  part,  or  corpus  spongiosum. 
The  urethra  passes  through  the  corpus  spongiosum.  The  penis  is  at- 
tached to  the  symphysis  pubis  by  its  root.  The  enlarged  extremity  or 
glans  penis  is  continuous  with  the  corpus  spongiosum.  The  integument 
covering  the  penis  forms  a  loose  fold  from  the  junction  of  the  glans  with 
the  body,  called  the  prepuce  or  foreskin. 

Structure — (a)  The  urethra  is  lined  by  stratified  pavement  epithelium 
in  the  prostatic  portion;  in  front  of  the  bulb  the  epithelium  becomes 
columnar,  whilst  at  the  fossa  naviculars  it  is  again  lined  with  stratified 
pavement  epithelium.  The  mucous  membrane  consists  chiefly  of  fibrous 
connective  tissue,  intermixed  with  which  are  many  elastic  fibres.     It  is 


644 


HANDBOOK    OF    PHYSIOLOGY. 


surrounded  by  unstriped  muscular  tissue.  In  the  intermediate  portion 
many  large  veins  run  amongst  the  bundles  of  muscular  tissue.  Many 
mucous  glands,  glands  of  Littre,  are  present. 

(b  )  The  corpora  cavernosa,  a  true  erectile  structure,  consist  of  a 
'matrix,  formed  of  trabecular  cerva,  made  up  chiefly  of  unstriped  muscle- 
fibres,  which  run  in  all  directions  from  the  fibrous  sheath,  and  from  the 
septum,  which  separates  the  two  corpora  cavernosa,  intermixed  with  con- 
nective tissue,  and  a  few  elastic  fibres.  The  matrix  is  arranged  in 
bundles,  and  thus  form  a  spongy  tissue,  lined  everywhere  with  endothe- 
lium, into  the  interstices  of  which,  the  venous  sinuses,  the  venous  blood 
passes.  The  trabecular  thus  constitute  the  greater  part  of  the  substance 
of  each  corpus  cavernosum.  The  venous  sinuses  anastomose  with  each 
other  to  form  plexuses.     The  arteries  run  in  the  muscular  trabecular. 

(c.)  The  corpus  spongiosum  urethra?  consists  of  an  inner  portion  or 


Fig.  434.— Erectile  tissue  of  the  human  penis,    a,  fibrous  trabeculae  with  their  ordinary  capil- 
laries; b,  section  of  the  venous  sinuses;  c,  muscular  tissue.    (Cadiat.j 


plexus  of  longitudinal  veins,  and  of  an  outer  or  really  cavernous  portion 
identical  in  structure  with  that  which  has  just  been  described.  The 
lymphatics  of  the  penis  are  very  numerous,  both  superficially  and  also 
around  the  urethra.     They  join  the  inguinal  glands. 

The  nerves,  derived  from  the  pudic  nerves  and  hypogastric  plexus, 
are  distributed  to  the  skin  and  mucous  membrane  and  to  the  corpora 
cavernosa  and  spongiosum  respectively.  The  nerves  are  provided  with 
end  bulbs  and  Pacinian  corpuscles  in  the  glans  penis,  and  form  also  a 
dense  subepithelial  plexus. 

Co  toper's  glands,  are  two  small  glands  the  ducts  of  which  open  into 
the  bulbous  part  of  the  urethra.  They  are  small  round  bodies,  of  the 
size  of  a  pea,  yellow  in  color,  resembling  the  sublingual  gland;  in  struc- 
ture they  are  compound  tubular  mucous  glands. 

The  Prostate  Gland. — The  prostate  is  situated  (Fig.  435)  at  the 
neck  of  the  urinary  bladder,  and  incloses  the  commencement  of  the 


THE   REPRODUCTIVE    SYSTEM. 


645 


urethra.  It  is  somewhat  chestnut-shaped.  It  measures  an  inch  and  a 
half  in  breadth,  and  an  inch  and  a  quarter  long,  and  half  an  inch  in 
thickness. 

Structure. — The  prostate  is  made  up  of  small  compound  tubular 
glands  imbedded  in  an  abundance  of  muscular  fibres  and  connective 
tissue. 

The  glandular  substance,  which  is  nearly  absent  from  the  front  part 
of  the  organ,  consists  of  numerous  small  saccules,  opening  into  elongated 
ducts,  which  unite  into  a  smaller  number  of  excretory  ducts.  TJie  acini 
of  the  upper  part  of  the  prostate,  are  small  and  hemispherical;  while  in 
the  middle  and  lower  parts  the  tubes  are  longer  and  more  convoluted. 
The  acini  are  of  two  kinds,  namely,  those  (a)  lined  with  a  single  layer  of 


Fig.  435.— Dissection  of  the  base  of  the  bladder  and  prostate  gland,  showing  the  vesiculae  semi- 
nales  and  vasa  deferentia.  a,  lower  surface  of  the  bladder  at  the  place  of  reflexion  of  the  peri- 
toneum; 6,  the  part  above  covered  by  the  peritoneum;  i,  left  vas  deferens,  ending  in  e,  the  ejacula 
tory  duct;  the  vas  deferens  has  been  divided  near  i,  and  all  except  the  vesical  portion  has  been 
taken  away;  s,  left  vesicula  seminalis  joining  the  same  duct;  s,  .s.  the  right  vas  deferens  and  right 
vesicula  seminalis.  which  has  been  unravelled;  p.  under  side  of  the  prostate  gland;  m,  part  of  the 
urethra;  u,  u,  the  ureters  (cut  short);  the  right  one  turned  aside.    (Haller.) 


thin  and  long  columnar  cells,  each  with  an  oval  nucleus  in  outer  part  of 
wall;  and  those  (b)  acini  resembling  the  foregoing,  but  with  a  second 
layer  of  small  cortical,  polyhedral,  or  fusiform  cells  between  the  mem- 
brana  propria  and  the  columnar  cells.  The  ducts,  twelve  to  twenty  in 
number,  open  into  the  urethra.  They  are  lined  by  a  layer  of  columnar 
cells,  beneath  which  is  a  layer  of  small  polyhedral  cells. 

The  tunica  adventitia  consists  of  dense  fibrous  tissue  of  two  layers, 
between  which  is  situated  a  plexus  of  veins.  Larger  vessels  pass  into  the 
interior  of  the  organ,  to  form  a  broad-meshed  capillary  system.    Nerves 


6±Q  HANDBOOK    OF    PHYSIOLOGY. 

and  numerous  large  ganglion  cells  surround  the  cortex.     Pacinian  bodies 
are  sometimes  found  in  the  substance  of  the  organ. 

The  muscular  tissue  of  the  prostate  not  only  forms  the  chief  part  of 
the  stroma  of  the  gland,  but  also  forms  a  continuous  layer  inside  the 
fibrous  sheath,  as  well  as  a  layer  surrounding  the  urethra,  which  is  con- 
tinuous with  the  sphincter  vesicae. 

Physiology  of  the  Sexual  Organs. 

A.  Of  the  Female. — In  the  process  of  development  in  the  ovary  of 
individual  Graafian  vesicles,  it  has  been  already  observed  that  as  each 
increases  in  size,  it  gradually  approaches  the  surface  of  the  ovary,  and 
when  fully  ripe  or  mature,  forms  a  little  projection  on  the  exterior.  Co- 
incident with  the  increase  of  size,  caused  by  the  augmentation  of  its 
liquid  contents,  the  external  envelope  of  the  distended  vesicle  becomes 
very  thin  and  eventually  bursts.  By  these  means  the  ovum  and  fluid 
contents  of  the  vesicle  are  liberated,  and  escape  on  the  exterior  of  the 
ovary,  whence  they  pass  into  the  Fallopian  tube  or  oviduct,  the  fimbri- 
ated processes  of  the  extremity  of  which  are  supposed  coincidentally  to 
grasp  the  ovary,  while  the  aperture  of  the  tube  is  applied  to  the  part  cor- 
responding to  the  matured  and  bursting  vesicle. 

In  animals  whose  capability  of  being  impregnated  occurs  at  regular 
periods,  as  in  the  human  subject,  and  most  Mammalia,  the  Graafian 
vesicles  and  their  contained  ova  appear  to  arrive  at  maturity,  and  the 
latter  to  be  discharged  at  such  periods  only.  But  in  other  animals,  e.  g.y 
the  common  fowl,  the  formation,  maturation,  and  discharge  of  ova  ap- 
pear to  take  place  almost  constantly. 

It  has  long  been  known,  that  in  the  so-called  oviparous  animals,  the 
separation  of  ova  from  the  ovary  may  take  place  independently  of  im- 
pregnation by  the  male,  or  even  of  sexual  union.  And  it  is  now  estab- 
lished thai  a  like  maturation  and  discharge  of  ova,  independently  of 
coition,  occurs  in  Mammalia,  the  periods  at  which  the  matured  ova  are 
separated  from  the  ovaries  and  received  into  the  Fallopian  tubes  being 
indicated  in  the  lower  Mammalia  by  the  phenomena  of  heat  or  rut;  in 
the  human  female,  although  not  always  with  exact  coincidence,  by  the 
phenomena  of  menstruation.  If  the  union  of  the  sexes  take  place,  the 
ovum  may  be  fecundated,  and  if  no  union  occur  it  perishes. 

That  this  maturation  and  discharge  occur  periodically,  and  only  dur- 
ing the  phenomena  of  heat  in  the  lower  Mammalia,  is  made  probable  by 
the  facts  that,  in  all  instances  in  which  Graafian  vesicles  have  been  found 
presenting  the  appearance  of  recent  rupture,  the  animals  were  at  the 
time,  or  had  recently  been,  in  heat;  that  on  the  other  hand,  there  is  no 
authentic  and  detailed  account  of  Graafian  vesicles  being  found  ruptured 
in  the  intervals  of  the  period  of  heat;  and  that  female  animals  do  not 


THE   REPRODUCTIVE    SYSTEM.  <">47 

admit   the   males,    and    never    become   impregnated,    except    at    those 
periods. 

Relation  of  Menstruation  to  the  Discharge  of  Ova. — The  human 
female  is  subject  to  the  same  law  as  the  females  of  ether  mammiferous 
animals;  namely,  in  her  as  in  them,  ova  are  matured  and  discharged 
from  the  ovary  independent  of  sexual  union.  This  maturation  and  dis- 
charge occur,  moreover,  periodically  at  or  about  the  epochs  of  menstrua- 
tion. 

The  evidence  of  the  periodical  discharge  of  ova  at  the  menstrual  pe- 
riods is  that  in  most  cases  in  which  signs  of  menstruation  have  been  found 
in  the  uterus,  follicles  in  a  state  of  maturity  or  of  rupture  have  been 
seen  in  the  ovary;  and  although  conception  is  not  confined  to  the  periods 
of  menstruation,  yet  it  is  more  likely  to  occur  about  a  menstrual  epoch 
than  at  other  times. 

The  exact  relation  between  the  discharge  of  ova  and  menstruation  is 
not  very  clear.  It  was  formerly  believed  that  the  monthly  flux  was  the 
result  of  a  congestion  of  the  uterus  arising  from  the  enlargement  and 
rupture  of  a  Graafian  follicle;  but  though  a  Graafian  follicle  is,  as  a 
rule,  ruptured  at  each  menstrual  epoch,  yet  several  instances  are  re- 
corded in  which  menstruation  has  occurred  where  no  Graafian  follicle 
can  have  been  ruptured,  and  on  the  other  hand  cases  are  known  where 
ova  have  been  discharged  in  amenorrhceic  women.  It  must  therefore  be 
admitted  that  menstruation  is  not  dependent  on  the  maturation  and  dis- 
charge of  ova. 

It  was,  moreover,  formerly  understood  that  ova  were  discharged 
towards  the  close  or  soon  after  the  cessation  of  a  menstrual  flow.  Obser- 
vations made  after  death,  and  facts  obtained  by  clinical  investigation, 
however,  do  not  support  this  view.  Rupture  of  a  Graafian  follicle  does 
not  happen  on  the  same  day  of  the  monthly  period  in  all  women.  It 
may  occur  towards  the  close  or  soon  after  the  cessation  of  a  flow;  but 
only  in  a  small  minority  of  the  subjects  examined  after  death  was  this 
the  case.  On  the  other  hand,  in  almost  all  such  subjects  of  which  there 
is  record,  rupture  of  the  follicle  appears  to  have  taken  place  before  the 
commencement  of  the  catamenial  flow.  Moreover,  the  custom  of  the 
Jews — a  prolific  race,  to  whom  by  the  Levitical  law  sexual  intercourse 
during  the  week  following  menstruation  was  forbidden — militates 
strongly  in  favor  of  the  view  that  conception  usually  occurs  before  and 
not  soon  after  a  menstrual  epoch,  and  necessarily,  therefore,  for  the  view 
that  ova  are  usually  discharged  before  the  catamenial  flow.  This,  to- 
gether with  the  anatomical  condition  of  the  uterus  just  before  the  cata- 
menia,  seems  to  indicate  that  the  ovum  fertilized  is  that  which  is  dis- 
charged in  connection  with  the  first  absent,  and  not  that  with  the  last 
present  menstruation. 

Though  menstruation  does  not  appear  to  depend  upon  the  discharge 


648 


HANDBOOK    OF  PHYSIOLOGY. 


of  ova,  yet  the  presence  of  the  ovaries  seems  necessary  for  the  perform- 
ance of  the  function;  for  women  do  not  menstruate  when  both  ovaries 
have  been  removed  by  operation.  Some  instances  have  been  recently 
recorded,  indeed,  of  a  sanguineous  discharge  occurring  periodically  from 
the  vagina  after  both  ovaries  have  been  previously  removed  for  disease; 
and  it  has  been  inferred  from  this  that  menstruation  is  a  function  inde- 
pendent of  the  ovary:  but  this  evidence  is  not  conclusive,  inasmuch  as  it 
is  possible  that  portions  of  ovarian  tisues  were  left  after  the  operation. 

Source  and  Characters  of  Menstrual  Discharge, — The  menstrual  dis- 
charge is  a  thin  sanguineous  fluid,  having  a  peculiar  odor.  It  is  of  a 
dark  color,  and  consists  of  blood,  epithelium,  and  mucus  from  the  ute- 


Fig.  436. 


Fig.  43; 


Fig.  438. 


Fig.  436.— Diagram  of  uterus  just  before  menstruation;  the  shaded  portion  represents  the  thick- 
ened mucous  membrane. 

Fig.  437.— Diagram  of  uterus  when  menstruation  has  just  ceased,  showing  the  cavity  of  the 
uterus  deprived  of  mucous  membrane. 

Fig.  438.— Diagram  of  uterus  a  week  after  the  menstrual  flux  has  ceased;  the  shaded  portion 
represents  renewed  mucous  membrane.    (J.  Williams.) 

rus  and  vagina,  serum,  and  the  debris  of  a  membrane  called  the  decidna 
menstrualis.  This  membrane  is  the  developed  mucous  membrane  of 
the  body  of  the  uterus.  It  does  not  extend  into  the  Fallopian  tube  or 
into  the  cavity  of  the  cervix.  It  attains  its  highest  state  of  development 
in  the  unimpregnated  organ  just  before  the  commencement  of  a  catame- 
nial  flow  (Fig.  436).  If  impregnation  take  place,  it  becomes  the  decidua 
vera;  -if  impregnation  fail,  the  membrane  undergoes  rapid  disintegration; 
its  vessels  are  laid  open  and  hemorrhage  follows.  The  blood  poured  out 
does  not  coagulate  in  consequence  partly  of  the  admixture  already  men- 


THE    REPRODUCTIVE    SYSTEM.  649 

tioned;  or,  very  possibly,  coagulation  occurs,  but  the  process  is  more  or 
less  spoiled,  and  what  clot  is  formed  is  broken  down  again,  so  as  to  imi- 
tate liquid  blood. 

Menstruation,  therefore,  is  not  the  result  of  congestion,  or  of  a  species 
of  erection,  but  of  a  destructive  process  by  which  the  decidua  or  nidus 
prepared  for  an  impregnated  ovum  is  carried  away.  It  is  not  a  sign  of 
the  capability  of  being  impregnated  as  much  as  of  disappointed  impreg- 
nation. 

Menstrual  Life. — The  occurrence  of  a  menstrual  discharge  is  one  of 
the  most  prominent  indications  of  the  commencement  of  -puberty  in  the 
female  sex;  though  its  absence  even  for  several  years  is  not  necessarily 
attended  with  arrest  of  the  other  characters  of  this  period  of  life,  or  with 
inaptness  for  sexual  union,  or  incapability  of  impregnation.  The  ave- 
rage time  of  its  first  appearance  in  females  of  this  country  and  others  of 
about  the  same  latitude,  is  from  fourteen  to  fifteen;  but  it  is  much  in- 
fluenced by  the  kind  of  life  to  which  girls  are  subjected,  being  accele- 
rated by  habits  of  luxury  and  indolence,  and  retarded  by  contrary  con- 
ditions. On  the  whole,  its  appearance  is  earlier  in  persons  dwelling  in 
warm  climes  than  in  those  inhabiting  colder  latitudes;  though  the  exten- 
sive investigations  of  Robertson  show  that  the  influence  of  temperature 
ou  the  development  of  puberty  has  been  exaggerated.  Much  of  the 
influence  attributed  to  climate  appears  due  to  the  custom  prevalent  in 
many  hot  countries,  as  in  Hindostan,  of  giving  girls  in  marriage  at  a 
very  early  age,  and  inducing  sexual  excitement  previous  to  the  proper 
menstrual  time.  The  menstrual  functions  continue  through  the  whole 
fruitful  period  of  a  woman's  life,  and  usually  cease  between  the  forty- 
fifth  and  fiftieth  years. 

The  several  menstrual  periods  usually  occur  at  intervals  of  a  lunar 
month,  the  duration  of  each  being  from  three  to  six  days.  In  some 
women  the  intervals  are  as  short  as  three  weeks  or  even  less;  while  in 
others  they  are  longer  than  a  month.  The  periodical  return  is  usually 
attended  by  pain  in  the  loins,  a  sense  of  fatigue  in  the  lower  limbs,  and 
other  symptoms,  which  are  different  in  different  individuals.  Menstrua- 
tion does  not  usually  occur  in  pregnant  women,  or  in  those  who  are 
suckling;  but  instances  of  its  occurrence  in  both  these  conditions  are  by 
no  means  rare. 

Corpus  Luteum. — Immediately  before,  as  well  as  subsequent  to, 
the  rupture  of  a  Graafian  vesicle,  and  the  escape  of  its  ovum,  certain 
changes  ensue  in  the  interior  of  the  vesicle,  which  result  in  the  produc- 
tion of  a  yellowish  mass,  termed  a  Corpus  luteum. 

"When  fully  formed  the  corpus  luteum  of  mammiferous  animals  is  a 
roundish  solid  body,  of  a  yellowish  or  orange  color,  and  composed  of  a 
number  of  lobules,  which  surround,  sometimes  a  small  cavity,  but  more 
frequently  a  small  stelliform  mass  of  white  substance,  from  which  deli- 


650 


HANDBOOK    OF    PHYSIOLOGY. 


cate  processes  pass  as  septa  between  the  several  lobules.  Very  often,  in 
the  cow  and  sheep,  there  is  no  white  substance  in  the  centre;  and  the 
lobules  projecting  from  the  opposite  walls  of  the  Graafian  vesicle  appear 
in  a  section  to  be  separated  by  the  thinnest  possible  lamina  of  semi- 
transparent  tissue. 

When  a  Graafian  vesicle  is  about  to  burst  and  expel  the  ovum,  it  be- 
comes highly  vascular  and  opaque;  and,  immediately  before  the  rupture 
takes  place,  its  walls  appear  thickened  on  the  interior  by  a  reddish  glu- 
tinous or  fleshy-looking  substance.  Immediately  after  the  rupture,  the 
inner  layer  of  the  wall  of  the  vesicle  appears  pulpy  and  flocculent.  It  is 
thrown  into  wrinkles  by  the  contraction  of  the  outer  layer,  and,  soon, 
red  fleshy  mammillary  processes  grow  from  it,  and  gradually  enlarge  till 
they  nearly  fill  the  vesicle,  and  even  protrude  from  the  orifice  in  the  ex- 
ternal covering  of  the  ovary.  Subsequently  this  orifice  closes,  but  the 
fleshy  growth  within  still  increases  during  the  earlier  period  of  preg- 


Fig.  439.— Corpora  lutea  of  different  periods.  B,  Corpus  luteum  of  about  the  sixth  week  after 
impregnation,  showing  its  plicated  form  at  that  period.  1,  substance  of  the  ovary;  2,  substance  of 
the  corpus  luteum;  3,  a  grayish  coagulum  in  its  cavity.  (Taterson. )  A,  corpus  luteum  two  days 
after  delivery;  D,  in  the  twelfth  week  after  delivery.    (Montgomery.) 


nancy,  the  color  of  the  substance  gradually  changing  from  red  to  yellow, 
and  its  consistence  becoming  firmer. 

The  corpus  luteum  of  the  human  female  (Fig.  439)  differs  from  that 
of  the  domestic  quadruped  in  being  of  a  firmer  texture,  and  having  more 
frequently  a  persistent  cavity  at  its  centre,  and  in  the  stelliform  cicatrix, 
which  remains  in  the  cases  where  the  cavity  is  obliterated,  being  pro- 
portionately of  much  larger  bulk.  The  quantity  of  yellow  substance 
formed  is  also  much  less:  and  although  the  deposit  increases  after  the 
vesicle  has  burst,  yet  it  does  not  usually  form  mammillary  growths  pro- 
jecting into  the  cavity  of  the  vesicle,  and  never  protrudes  from  the  ori- 
fice, as  is  the  case  in  other  Mammalia.  It  maintains  the  character  of  a 
uniform,  or  nearly  uniform,  layer,  which  is  thrown  into  wrinkles,  in 


THE   REPRODUCTIVE    SYSTEM.  H51 

consequence  of  the  contraction  of  the  external  tunic  of  the  vesicle.  After 
the  orifice  of  the  vesicle  has  closed,  the  growth  of  the  yellow  substance 
continues  during  the  first  half  of  pregnancy,  till  the  cavity  is  reduced  to 
a  comparatively  small  size,  or  is  obliterated;  in  the  latter  case,  merely  a 
white  stelliform  cicatrix  remains  in  the  centre  of  the  corpus  luteum. 

An  effusion  of  blood  generally  takes  place  into  the  cavity  of  the  Graaf- 
ian vesicle  at  the  time  of  its  rupture,  especially  in  the  human  subject, 
but  it  has  no  share  in  forming  the  yellow  body;  it  gradually  loses  its 
coloring  matter,  and  acquires  the  character  of  a  mass  of  fibrin.  The 
serum  of  the  blood  sometimes  remains  included  within  a  cavity  in  the 
centre  of  the  coagulum,  and  then  the  decolorized  fibrin  forms  a  mem- 
braniform  sac,  lining  the  corpus  luteum.  At  other  times  the  serum  is 
removed,  and  the  fibrin  constitutes  a  solid  stelliform  mass. 

The  yellow  substance  of  which  the  corpus  luteum  consists,  both  in 
the  human  subject  and  in  the  domestic  animals,  is  a  growth  from  the 
inner  surface  of  the  Graafian  vesicle,  the  result  of  an  increased  develop- 
ment of  the  cells  forming  the  membrana  granulosa,  which  naturally 
lines  the  internal  tunic  of  the  vesicle. 

The  first  changes  of  the  internal  coat  of  the  Graafian  vesicle  in  the 
process  of  formation  of  a  corpus  luteum  seem  to  occur  in  every  case  in 
which  an  ovum  escapes;  as  well  in  the  human  subject  as  in  the  domes- 
tic quadrupeds.  If  the  ovum  is  impregnated,  the  growth  of  the  yellow 
substance  continues  during  nearly  the  whole  period  of  gestation,  and 
forms  the  large  corpus  luteum  commonly  described  as  a  characteristic 
mark  of  impregnation.  If  the  ovum  is  not  impregnated,  the  growth  of 
yellow  substance  on  the  internal  surface  of  the  vesicle  proceeds,  in  the 
human  ovary,  no  further  than  the  formation  of  a  thin  layer,  which 
shortly  disappears;  but  in  the  domestic  animals  it  continues  for  some 
time  after  the  ovum  has  perished,  and  forms  a  corpus  luteum  of  con- 
siderable size.  The  fact  that  a  structure,  in  its  essential  characters 
similar  to,  though  smaller  than,  a  corpus  luteum  observed  during  preg- 
nancy, is  formed  in  the  human  subject,  independent  of  impregnation  or 
of  sexual  union,  coupled  with  the  varieties  in  size  of  corpora  lutea 
formed  during  pregnancy,  necessarily  renders  unsafe  all  evidence  of 
previous  impregnation  founded  on  the  existence  of  a  corpus  luteum  in 
the  ovary. 

The  following  table  by  Dalton,  expresses  well  the  differences  between 
the  corpus  luteum  of  the  pregnant  and  unimpregnated  condition  respec- 
tively:— 


652 


HANDBOOK    OF   PHYSIOLOGY. 


Corpus  Luteum  of 
Menstruation. 


Corpus  Luteum  of 
Pregnancy. 


At  the  end   of 

three  iveeks   . 

One  month  .     . 


Two  months 

Six  months  .     . 
Nine  months,   . 


Three-quarters  of  an  inch  in  diameter;  central  clot  red- 
dish; convoluted  wall  pale. 


Smaller;  convoluted 
wall  bright  yellow; 
clot  still  reddish. 

Eeduced  to  the  condi- 
tion of  an  insignifi- 
cant cicatrix. 

Absent. 


Larger;  convoluted  wall  bright 
yellow;  clot  still  reddish. 

Seven-eighths  of  an  inch  in  di- 
ameter; convoluted  wall  bright 
yellow;  clot  perfectly  decolor- 
ized. 

Still  as  large  as  at  end  of  second 
month;    clot  fibrinous;   convo- 
luted wall  paler. 
Absent.  One-half  an   inch    in   diameter; 

central  clot  converted  into  a 
radiating  cicatrix;  the  exter- 
nal wall  tolerably  thick  and 
convoluted,  but  without  any 
bright  yellow  color. 

B.  Of  the  Male. — In  order  that  the  ovum  should  be  fecundated  or 
impregnated,  it  is  necessary  that  it  should  meet  with  the  seminal  fluid 
of  the  male.  This  is  accomplished  by  the  junction  of  the  sexes  in  the 
act  of  coition,  whereby  the  seminal  fluid  is  discharged  into  the  neigh- 
borhood of,  if  not  within,  the  cervix  uteri.  Before  considering  the 
changes  which  are  produced  in  the  ovum  by  impregnation,  it  will  be  as 
well  to  describe  the  nature  of  the  seminal  fluid.  This  consists  essen- 
tially of  the  semen  secreted  by  the  testicles  :  and  to  this  are  added,  a 
material  secreted  by  the  vesiculge  seminales,  as  well  as  the  secretion  of 
the  prostate  gland,  and  of  Oowper's  glands.  Portions  of  these  several 
fluids  are  discharged,  together  with  the  proper  secretion  of  the  testicles. 

The  semen  is  a  viscid,  whitish,  albuminous  fluid  of  a  peculiar  odor. 
It  contains  epithelium,  granules  or  colorless  particles,  and  large  num- 
bers of  spermatozoa,  which  are  the  characteristic  and  essential  element. 
The  spermatozoa  are  minute  bodies  each  consisting  of  a  flattened  oval 
head  and  attached  to  it  a  long,  slender,  tapering,  mobile  flagellum  or 
tail. 

In  some  forms  of  spermatozoa  there  is  a  small  middle  piece  inter- 
posed between  the  head  and  the  tail.  The  head  is  about  ^o-gth  inch 
long  and  Tofo otn  incn  broad.  The  tail  is  about  lir\ ^th  to  TIFV yth  inch 
long.  The  spermatozoa  possess  the  power  of  active  movement,  and  it  is 
by  this  sinuous,  cilia-like  movement  that  they  are  propelled  in  the  female 
and  so  helped  in  their  progress  to  meet  the  ovum. 

Spermatozoa. — On  examining  the  spermatozoon  of  Triton  crista- 
tus,  one  of  the  Amphibia  which  possess  the  largest  spermatozoa  of  all 
Vertebrate  animals,  Gibbes  found  that  the  organism  consisted  of  (a)  a 


THE    REPRODUCTIVE    SYSTEM. 


65 


long  pointed  head,  at  the  base  of  which  18(b),  an  elliptical  structure 
joining  the  head  to  (c),  a  long  filiform  body;  (d),  a  fine  filament,  much 
longer  than  the  body,  is  connected  with  this  latter  by  (e),  a  homogene- 
ous membrane. 

The  head.,  as  it  appears  in  the  fresh  specimen,  has  a  different  refrac- 
tive power  from  that  of  the  rest  of  the  organism,  and  with  a  high  power 
appears  to  be  a  light  green  color;  there  is  also  a  central  line  running  up 
it,  from  which  it  appears  to  be  hollow. 


Fig.  410. 


Fig.  441. 


Fig.  440.— Spermatic  filaments  from  the  human  vas  deferens.    1,  magnified  300  diameters;  2, 
magnified  800  diameters;  a,  from  the  side;  b,  from  above.    (From  Kolliker.) 
Fig.  441.— Spermatozoa.    1,  Of  salamander;  2,  human.    iH.  Gibbs.) 


The  elliptical  structure  at  the  base  of  the  head  connects  it  with  the 
long  thread-like  body,  and  tin-  filament  springs  from  it. 

Whilst  the  spermatozoon  is  living,  this  filament  is  in  constant  mo- 
tion;   at  first  this  is  so  quick  that   it  is  difficult  to  see  it,  but  as  its 


654  HANDBOOK    OF   PHYSIOLOGY. 

vitality  becomes  impaired  the  motion  gets  slower,  and  it  is  then  easily 
perceived  to  be  a  continuous  waving  from  side  to  side. 

The  spermatozoa  of  all  Mammalia  examined,  consisting  of  Man, 
Bull,  Dog,  Horse,  Cat,  Pig,  Mouse,  Rat,  Guinea-pig,  had,  instead  of 
the  long-pointed  head  of  the  Amphibian,  a  blunt  thick  process  of  dif- 
ferent shapes  in  the  different  animals:  and  from  the  root  or  neck  of  this 
proceeded  the  long  filament,  just  as  in  the  Amphibia,  only  so  delicate  as 
to  be  invisible  except  with  very  high  powers. 

In  Man  the  head  (Fig.  441)  is  club-shaped,  and  from  its  base  springs 
the  very  delicate  filament,  which  is  three  or  four  times  as  long  as  the 
body;  and  the  membrane  which  attaches  it  to  the  body  is  much  broader, 
and"  allows  it  to  lie  at  a  greater  distance  from  the  body  than  in  the 
spermatozoa  of  any  other  Mammal  examined. 

From  his  investigations,  Gribbes  concluded: — 1st.  That  the  head  of 
the  spermatozoon  is  inclosed  in  a  sheath,  which  is  a  continuation  of  the 
membrane  which  surrounds  the  filament,  and  connects  it  to  the  body, 
acting  in  fact  the  part  of  a  mesentery.  2dly.  That  the  substance  of  the 
head  is  quite  distinct  in  its  composition  from  the  elliptical  structure,  the 
filament  and  the  long  body,  and  that  it  is  readily  acted  on  by  alkalies; 
these  reagents  have  no  effect,  however,  on  the  other  part,  excepting  the 
membranous  sheath.  3dly.  That  this  elliptical  structure  has  its  ana- 
logue in  the  Mammalian  spermatozoon,  in  the  one  case  the  head  is 
drawn  out  as  a  long  pointed  process,  in  the  other  it  is  of  a  globular 
form,  and  surrounds  the  elliptical  structure.  4thly.  That  the  motive 
power  lies,  in  a  great  measure,  in  the  filament  and  the  membrane  attach- 
ing it  to  the  body. 

The  spermatozoa  are  derived  from  the  breaking  up  of  the  seminal 
cells  or  daughter  cells.     They  must  be  looked  upon  as  modified  cells. 

The  occurrence  of  spermatozoa  in  the  impregnating  fluid  of  nearly 
all  classes  of  animals,  proves  that  they  are  essential  to  the  process  of  im- 
pregnation, and  their  actual  contact  with  the  ovum  is  necessary  for  its 
development. 

The  seminal  fluid  is,  probably,  after  the  period  of  puberty  secreted 
constantly,  though,  except  under  excitement,  very  slowly,  in  the  tubules 
of  the  testicles.  From  these  it  passes  along  the  vasa  deferentia  into  the 
vesiculae  seminales,  whence,  if  not  expelled  in  emission,  it  may  be  dis- 
charged, as  slowly  as  it  enters  them,  either  with  the  urine,  which  may 
remove  minute  quantities,  mingled  with  the  mucus  of  the  bladder  and 
the  secretion  of  the  prostate,  or  from  the  urethra  in  the  act  of  defae- 
cation. 

To  the  vesiculae  seminales  a  double  function  may  be  assigned:  for 
they  both  secrete  some  fluid  to  be  added  to  that  of  the  testicles,  and  serve 
as  reservoirs  for  the  seminal  fluid.  The  former  is  their  most  constant 
and  probably  most  important  office;  for  in  the  horse,  bear,  guinea-pig, 
and  several  other  animals,  in  whom  the  vesiculae  seminales  are  large  and 
of  apparently  active  function,  they  do  not  communicate  with  the  vasa 
deferentia,  but  pour  their  secretions,  separately,  though  it  maybe  simul- 
taneously, into  the  urethra.     In  man,  also,  when  one  testicle  is  lost,  the 


THE    REPRODUCTIVE    SYSTEM.  (i.V) 

corresponding  vesicula  seminalia  suffers  no  atrophy,  though  its  function 
as  a  reservoir  is  abrogated.  But  how  the  vesicula?  seminales  act  as 
secreting  organs  is  unknown;  the  peculiar  brownish  fluid  which  they 
contain  after  death  does  not  properly  represent  their  secretion,  for  it  is 
different  in  appearance  from  anything  discharged  during  life,  and  is 
mixed  with  semen.  It  is  nearly  certain,  however,  that  their  secretion 
contributes  to  the  proper  composition  of  the  impregnating  fluid;  for  in 
all  the  animals  in  whom  they  exist,  and  in  whom  the  generative  func- 
tions are  exercised  at  only  one  season  of  the  year,  the  vesicula?  seminales, 
whether  they  communicate  with  the  vasa  deferentia  or  not,  enlarge 
commensurately  with  the  testicles  at  the  approach  of  that  season. 

That  the  vesicula?  are  also  reservoirs  in  which  the  seminal  fluid  may 
lie  for  a  time  previous  to  its  discharge,  is  shown  by  their  commonly  con- 
taining the  seminal  filaments  in  larger  abundance  than  any  portion  of 
the  seminal  ducts  themselves  do.  The  fluid-like  mucus,  also,  which  is 
often  discharged  from  the  vesicula?  in  straining  during  defalcation,  com- 
monly contains  seminal  filaments.  But  no  reason  can  be  given  why  this 
office  of  the  vesicula?  should  not  be  equally  necessary  to  all  the  animals 
Avhose  testicles  are  organized  like  those  of  man,  or  why  in  many  animals 
the  vesicular  are  wholly  absent. 

There  is  an  equally  complete  want  of  information  respecting  the 
secretions  of  the  prostate  and  Cowper's  glands,  their  nature  and  purposes. 
That  they  contribute  to  the  right  composition  of  the  impregnating  fluid, 
is  shown  both  by  the  position  of  the  glands  and  by  their  enlarging  with 
the  testicles  at  the  approach  of  an  animal's  breeding  time.  But  that 
they  contribute  only  a  subordinate  part  is  shown  by  the  fact,  that,  when 
the  testicles  are  lost,  though  these  other  organs  be  perfect,  all  procrea- 
tive  power  ceases. 

The  fluid  part  of  the  semen  or  liquor  seminis  has  not  been  satisfac- 
torily analyzed:  but  Henle  says  it  contains  fibrin,  because  shortly  after 
being  discharged,  flocculi  form  in  it  by  spontaneous  coagulation,  and 
leave  the  rest  of  it  thinner  and  more  liquid,  so  that  the  filaments  move 
in  it  more  actively. 

Nothing  has  shown  what  it  is  that  makes  this  fluid  with  its  corpuscles 
capable  of  impregnating  the  ovum,  or  (what  is  yet  more  remarkable)  of 
giving  to  the  developing  offspring  all  the  characters,  in  features,  size, 
mental  disposition,  and  liability  to  disease,  which  belong  to  the  father. 
This  is  a  fact  wholly  inexplicable:  and  is,  perhaps,  only  exceeded  in 
strangeness  by  those  facts  which  show  that  the  seminal  fluid  may  exert 
such  an  influence,  not  only  on  the  ovum  which  it  impregnates,  but, 
through  the  medium  of  the  mother,  on  many  which  are  subsequently 
impregnated  by  the  seminal  fluid  of  another  male. 


CHAPTER    XXIII. 

DEVELOPMENT. 

Changes  which  occur  in  the  Ovum. 

Of  the  changes  which  take  place  in  the  ovum,  some  occur  before  and 
are  as  it  were  preparatory  to  impregnation,  and  others  ensue  after 
impregnation.  It  will  be  as  well  to  consider  the  respective  changes 
separately. 

(1.)  Changes  prior  to  Impregnation. — These  changes  especially 
concern  the  germinal  vesicle,  and  have  been  observed  chiefly  in  the  ova  of 
low  types.  The  ovum  when  ripe  and  detached  from  the  ovary  consists, 
it  will  be  remembered,  of  a  granular  yolk  inclosed  within  the  protoplas- 
mic zona  pellucida,  and  containing  the  germinal  vesicle  and  germinal 
spot  situated  eccentrically.  The  yelk  granules  are  of  different  sizes, 
from  the  minutest  molecules  up  to  a  diameter  of  y-gVoth  to  ttW^1  °f  an 
inch.  The  germinal  vesicle  consists  of  reticulated  protoplasm  inclosed 
in  a  distinct  membrane,  and  containing  one  or  more  nucleoli  or  germinal 
spots.  The  primary  change  observed  in  the  ovum  consists  in  alterations 
in  the  shape  of  the  vesicle,  the  disappearance  of  its  protoplasmic  reticu- 
lum, and  of  its  inclosing  membrane,  with  a  consequent  indentation  and 
indistinctness  of  its  outline.  Its  protoplasm  becomes  to  a  considerable 
extent  confounded  with  the  yelk  substance,  and  its  germinal  spot  disap- 
pears. The  next  step  in  the  process  is  the  appearance  in  the  yelk  of  two 
stars  in  a  clear  space  near  the  poles  of  the  vesicle  elongated  to  a  certain 
extent,  and  from  this  results  a  nuclear  spindle,  corresponding  to  a  nucleus 
in  the  process  of  division,  with  the  stars  at  either  end  lying  near  the 
surface  of  the  yelk.  This  spindle  next  becomes  vertical,  and  the  star 
nearer  the  surface  protrudes  from  the  ovum  enveloped  in  a  protoplasmic 
mass,  which  by  constriction  form  the  first  polar  cell.  A  second  polar 
cell  arises  in  the  same  way.  From  the  remainder  of  the  spindle  within 
the  yelk  two  or  three  vesicles  arise,  and  by  the  junctiou  of  these  a  single 
nucleus  is  formed,  which  is  called  the  female  pro-nucleus.  This  is  clearly 
derived  from  the  original  germinal  vesicle.  It  must  be  remembered  that 
these  changes  have  been  so  far  observed  only  in  a  certain  number  of 
instances.  It  is  very  possible,  not  to  say  probable,  that  such  changes 
are  universal  in  the  animal  kingdom  (Balfour). 


DEVELOPMENT.  657 

Balfour's  view  as  to  the  formation  of  the  polar  bodies  may  be  given 
in  his  own  words: — "  My  view  amounts  to  the  following,  viz.,  that  after 
the  formation  of  the  polar  cells,  the  remainder  of  the  germinal  vesicle 
within  the  ovum  (the  female  pro-nucleus)  is  incapable  of  further  devel- 
opment without  the  addition  of  the  nuclear  part  of  the  male  element 
(spermatozoon),  and  that  if  polar  cells  were  not  formed,  parthenogenesis 
might  normally  occur." 

(2.)  Changes  following  Impregnation. — The  process  of  impreg- 
nation of  the  ovum  has  been  observed  most  accurately  in  the  lower  types. 
In  mammalia,  although  spermatozoa  pass  in  numbers  through  the  yelk 
envelope,  yet  their  further  progress  is  only  inferred  from  observations  on 
the  lower  animals.  The  process  in  asterias  glacialis,  according  to  Bal- 
four, is  as  follows: — The  head  of  a  single  spermatozoon  joins  with  an 
elevation  of  the  yelk  substance,  the  tail  remaining  motionless,  and  then 
disappearing.  The  head  enveloped  in  the  protoplasm  then  sinks  into 
the  yelk  and  becomes  a  nucleus,  from  which  the  yelk  substance  is 
arranged  in  radiating  lines.  This  is  the  male  pro-nucleus.  At  first,  at 
some  distance  from  the  female  pro-nucleus,  it  after  a  while  approaches 
nearer,  and  the  female  pro-nucleus,  which  was  before  inactive,  becomes 
active.  The  nuclei  at  last  meet  and  unite.  The  result  of  their  union  is 
the  first  segmentation  sphere,  or  Blasto-sphere.  It  is  a  nucleated  proto- 
plasmic cell.  The  changes  which  have  resulted  in  the  formation  of  the 
Blasto-sphere  or  primitive  segmentation  germ  are  followed  by  the  process 
known  as  segmentation  of  the  yelk. 

This  process  and  the  earlier  stages  in  development  are  so  fundamen- 
tally similar  in  all  vertebrate  animals,  from  Fishes  up  to  Man,  that  the 
gaps  existing  in  our  knowledge  of  the  process  in  the  higher  Mammalia, 
such  as  man,  may  be,  in  part,  at  any  rate,  filled  up  by  the  more  accurate 
knowledge  which  we  possess  of  the  development  of  the  ovum  in  such 
animals  as  the  trout,  frog,  and  fowl. 

One  important  distinction  between  the  ova  of  various  Vertebrata 
should  be  remembered.  In  the  hen's  egg,  besides  the  shell  and  the  white 
or  albumen,  two  other  structures  are  to  be  distinguished—  the  germ, 
often  called  the  cicatricula  or  "tread,"' and  the  yelk,  inclosed  in  its 
vitelline  membrane. 

The  germ  is  (as  was  mentioned  in  the  description  already  given) 
essentially  a  cell,  consisting  of  protoplasm  inclosing  a  nucleus  and  nucle- 
olus. It  alone  participates  in  the  process  of  segmentation,  the  great  mass 
of  the  yelk  (food-yelk)  remaining  quite  unaffected  by  it.  Since  only  the 
germ,  which  forms  but  a  small  portion  of  the  yelk,  undergoes  segmenta- 
tion, the  ovum  is  called  meroblastic. 

In  the  Mammalia,  on  the  other  hand,  there  is  no  large  unsegmented 
mass  corresponding  to  the  food-yelk  of  birds;  the  entire  ovum  undergoes 
segmentation,  and  is  hence  termed  holoblastic. 

The  eggs  of  Fishes,  Reptiles,  and  Birds,  are  meroblastic,  while  those 
of  Amphibia  and  Mammalia  are  holoblastic. 
42 


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HANDBOOK    OF    PHY3IOLOGY. 


Of  the  changes  which  the  mammalian  ovum  undergoes  previous  to 
the  formation  of  the  embryo,  those  which  occur  while  it  is  still  in  the 
ovary  are  independent  of  impregnation:  others  take  place  after  it  has 
reached  the  Fallopian  tube.  The  knowledge  we  possess  of  these  changes 
is  derived  almost  exclusively  from  observations  on  the  ova  of  the  bitch 

and  rabbit:  but  it  may  be  inferred  that 
analogous  changes  ensue  in  the  human 
ovum. 

As  the  ovum  approaches  the  middle  of 
the  Fallopian  tube,  it  begins  to  receive  a 
new  investment,  consisting  of  a  layer  of 
transparent  albuminous  or  glutinous  sub- 
stance, which  forms  upon  the  exterior  of 
the  zona  pellucida.  It  is  at  first  exceed- 
ingly fine,  and,  owing  to  this,  and  to  its 
transparency,  is  not  easily  recognized,  but 
at  the  lower  part  of  the  Fallopian  tube  it 
acquires  considerable  thickness. 

Segmentation. — The  first  visible  re- 
sult of  fertilization  is  a  slight  amoeboid 
movement  in  the  protoplasm  of  the  ovum: 
this  has  been  observed  in  some  fish,  in 
the  frog,  and  in  some  mammals.  Im- 
mediately succeeding  to  this  the  process 
of  segmentation  commences,  and  is  com- 
pleted during  the  passage  of  the  ovum 
through  the  Fallopian  tube.  In  mam- 
mals, in  which  the  process  is  an  example 
of  complete  segmentation,  the  yelk  becomes 
constricted  in  the  middle,  and  surrounded 
by  a  furrow  which  gradually  deepening, 
at  length  cuts  it  in  half,  while  the  same 
process  begins  almost  immediately  in  each 
half  of  the  yelk,  and  cuts  it  also  in  two. 
The  same  process  is  repeated  in  each  of 
the  quarters,  and  so  on,  until  at  last  by 
continual  cleavings,  the  whole  yelk  is 
changed  into  a  mulberry-like  mass  of 
small  and  more  or  less  rounded  bodies 
sometimes  called  vitelline  spheres,  the 
whole  still  inclosed  by  the  zona  pellucida 
or  vitelline  membrane  (Fig.  442).  Each  of  these  little  spherules  con- 
tains a  transparent  vesicle,  like  an  oil-globule,  which  is  seen  with  cliffi- 


Fig.  442.— Diagrams  of   the  various 
stages  of  cleavage  of  the  yelk.    (Dalton.) 


DEVELOPMENT.  »'>.">'.» 

culty,  on  account  of  its  being  enveloped  by  the  yelk-granules  which 
adhere  closely  to  its  surface. 

The  cause  of  this  singular  subdivision  of  the  yelk  is  quite  obseure: 
though  the  immediate  agent  in  its  production  seems  to  be  the  central 
vesicle  contained  in  each  division  of  the  yelk.  Originally  there  was 
probably  but  one  vesicle,  situated  in  the  centre  of  the  entire  granular 
mass  of  the  yelk,  and  probably  derived  in  the  manner  already  described 
from  the  germinal  vesicle.  This  divides  and  subdivides:  each  succes- 
sive division  and  subdivision  of  the  vesicle  being  accompanied  by  a  cor- 
responding division  of  the  yelk. 

About  the  time  at  which  the  Mammalian  ovum  reaches  the  uterus, 
the  process  of  division  and  subdivision  of  the  yelk  appears  to  have  ceased, 
its  substance  having  been  resolved  into  its  iiltimate  and  smallest  divi- 
sions, while  its  surface  presents  a  uniform  finely  granular  aspect,  instead 
of  its  late  mulberry-like  appearance.  The  ovum,  indeed,  appears  at 
first  sight  to  have  lost  all  trace  of  the  cleavage  process,  and,  with  the 
exception  of  being  paler  and  more  translucent,  almost  exactly  resembles 
the  ovarian  ovum,  its  yelk  consisting  apparently  of  a  confused  mass  of 
finely  granular  substance.  But  on  a  more  careful  examination,  it  is 
found  that  these  granules  are  aggregated  into  numerous  minute  sphe- 
roidal masses,  each  of  which  contains  a  clear  vesicle  of  nucleus  in  its 
centre,  and  is,  in  fact,  an  embryonal  cell.  The  zona  pellucida,  and  the 
layer  of  albuminous  matter  surrounding  it,  have  at  this  time  the  same 
character  as  when  at  the  lower  part  of  the  Fallopian  tube. 

The  passage  of  the  ovum,  from  the  ovary  to  the  uterus,  occupies 
probably  eight  or  ten  days  in  the  human  female. 

"When  the  peripheral  cells,  which  are  formed  first,  are  fully  devel- 
oped, they  arrange  themselves  at  the  surface  of  the  yelk  into  a  kind  of 
membrane,  and  at  the  same  time  assume  a  polyhedral  shape  from  mu- 
tual pressure,  so  as  to  resemble  pavement  epithelium.  The  deeper  cells 
of  the  interior  pass  gradually  to  the  surface  and  accumulate  there,  thus 
increasing  the  thickness  of  the  membrane  already  formed  by  the  more 
superficial  layer  of  cells,  while  the  central  part  of  the  yelk  remains  filled 
only  with  a  clear  fluid.  By  this  means  the  yelk  is  shortly  converted  into 
a  kind  of  secondary  vesicle,  the  walls  of  which  are  composed  externally 
of  the  original  vitelline  membrane,  and  within  by  the  newly  formed  cel- 
lular layer,  the  blastodermic  or  germinal  membrane,  as  it  is  called. 

Segmentation  in  the  Chick. — The  embryo  chick  affords  an  illus- 
tration of  what  is  known  as  incomplete  or  partial  segmentation,  or  me- 
roblastic  segmentation.  In  the  youngest  ova  the  germinal  vesicle  is 
situated  subcentrally,  but  as  development  proceeds  it  passes  to  the  peri- 
phery, and  the  protoplasm  surrounding  it  remaining  free  from  yelk 
granules,  the  germinal  disc  is  formed.  This  germinal  disc  is  not  marked 
out  by  any  sharp  line  from  the  remaining  protoplasm,  but  passes  iusen- 


660 


HANDBOOK    OF   PHYSIOLOGY. 


sibly  into  it.  The  first  change  consists  ia  the  appearance  of  a  furrow 
running  across  the  disc  dividing  it  into  two;  it  does  not  extend  across 
the  whole  breadth.  A  second  furrow,  at  right  angles,  cutting  the  first 
a  little  eccentrically,  next  appears,  and  the  disc  is  thus  cut  into  four 
quadrants.  The  furrows  do  not  extend  through  the  whole  thickness  of 
the  disc,  and  the  segments  are  not  separated  out  on  the  lower  aspect. 
The  quadrants  are  next  bisected  by  radiating  furrows,  and  the  disc  is 
thus  divided  into  eight  parts.  The  central  portion  of  each  segment  is 
now  cut  off  from  the  peripheral  furrow,  so  that  a  number  of  smaller 
central  and  larger  peripheral  portions  result.  As  the  primary  division 
was  eccentric  and  the  succeeding  followed  the  same  plan,  there  results  a 
bilateral  symmetry;  but  the  relation  of  the  axis  of  symmetry  and  the 
long  axis  of  the  embryo  is  not  known.  Eapid  division  of  the  segments 
by  furrows  in  various  directions  now  ensues,  and  the  small  central 
portions  are  more  rapidly  broken  up  than  the  larger,  and  therefore  be- 
come more  numerous.  During  this  superficial  segmentation  a  similar 
process  goes  on  throughout  the  whole  mass,  and  division  goes  on  not 


Fig  443.—  Vertical  section  of  area  pellucida  and  area  opaca  Qeft  extremity  of  figure)  of 
blastoderm  of  a  fresh  laid  egg  (unincubated).  S,  superficial  layer  corresponding  to  epiblast;  £», 
deeper  layer,  corresponding  to  hypoblast,  and  probably  in  part  to  mesoblast;  Af,  large  "  formative 
cells,"  filled  with  yelk  granules,  and  lying  on  the  floor  of  the  segmentation  cavity;  A,  the  white 
yelk  immediately  underlying  the  segmentation  cavity  (Strieker). 

only  by  vertical  but  also  by  horizontal  furrows.  The  result  of  this  pro- 
cess of  segmentation  is  that  the  original  germinal  disc  is  cut  up  into 
a  large  number  of  small  rounded  protoplasmic  cells,  small  in  the  centre, 
larger  to  the  periphery,  and  that  the  superficial  cells  are  smaller  than 
those  below:  the  two  original  layers  of  the  blastoderm  are  thus  early  re- 
presented. 

The  process  of  segmentation  proceeds  at  the  periphery  of  the  germi- 
nal disc,  and  at  the  same  time  further  division  of  the  cells  at  the  cen- 
tre proceeds.  The  nucleus  of  the  original  cells  divides  coincidently  with 
the  protoplasm,  and  so  it  comes  that  the  protoplasmic  masses  are  nucle- 
ated; and  besides  this,  nuclei  derived  from  the  original  nucleus  are 
found  in  the  ovum  below  the  area  of  segmentation,  and  from  these,  by 
the  protoplasm  which  surrounds  them  being  constricted  off  with  them, 
supplementary  segmentation  masses  come  to  be  formed.  The  blasto- 
derm is  thus  formed  as  the  result  of  segmentation,  and  between  it  and 
the  subjacent  white  yelk  is  a  cavity  containing  fluid.     The  segmentation 


DEVELOPMENT.  661 

having  been  completed  towards  the  centre,  although  it  still  proceeds  at 
the  periphery,  the  superficial  layer  of  the  blastoderm  becomes  a  layer  of 
columnar  nucleated  cells,  and  the  lower  layer  consists  of  larger  masses 
indistinctly  nucleated,  still  granular  and  rounded,  irregularly  disposed. 
In  the  segmentation  cavity  are  the  supplementary  segmentation  masses 
or  formative  cells. 

When  the  egg  is  incubated,  rapid  changes  take  place  in  the  blasto- 
derm, resulting  in  the  formation  first  of  all  of  two,  then  of  the  three 
layers,  which  have  been  already  mentioned  in  the  first  chapter.  The  su- 
perficial layer,  or  Epiblast,  does  not  at  first  enter  into  these  changes, 
hut  continues  to  be  a  layer  of  nucleated  columnar  cells.  But  in  the 
lower  layer  of  larger  rounded  cells,  certain  of  the  cells  become  flattened 
horizontally,  their  granules  disappear,  and  the  nuclei  become  distinct. 
A  membrane  of  flattened  nucleated  cells  is  then  formed,  first  of  all 
towards  the  centre  of  the  area,  afterwards  peripherally  also:  this  is  the 
Hypoblast.  Between  the  two  layers  some  cells,  not  belonging  to  either 
layer,  remain.  These  cells  are  almost  entirely  at  the  back  part  of  the 
area.  The  formations  of  the  intermediate  layer  of  mesoblast  is  more 
complicated,  and  will  now  be  described. 

At  this  period  it  is  necessary  to  return  to  the  surface  view  of  the 
blastoderm.  Before  incubation  it  is  seen  to  consist  of  a  more  or  less  cir- 
cular transparent  area,  the  area  pellucida,  surrounded  by  an  opaque 
rim,  which  is  called  the  area  opaca.  The  area  opaca  rests  upon 
the  white  yelk:  beneath  the  area  pellucida  is  a  cavity  containing  fluid. 
In  the  centre  of  the  area  pellucida  is  a  white  shining  spot,  or  nucleus  of 
Pander,  shining  through.  The  nucleus  of  Pander  is  in  the  upper  dilated 
extremity  of  the  flask-shaped  accumulation  of  white  yelk  upon  which 
the  blastoderm  rests. 

The  yellow  yelk  consists  of  spheres  25  /.i  to  100  /<  in  diameter,  filled 
with  highly  refractive  granules  of  an  albuminous  nature,  and  the  white 
yelk  being  distinguished  from  the  yellow  not  only  by  its  lighter  color, 
but  also  because  its  vesicles  are  smaller  than  those  of  the  yellow.  Each 
contains  a  highly  refractive  body.  Some  large  spheres  contain  a  number 
of  spherules.  Some  of  these  are  vacuolated.  The  white  yelk  not  only 
envelopes  the  yellow  yelk  in  a  thin  layer,  and  merges  with  the  central 
flask-shaped  mass,  already  meutioued,  but  also  is  found  in  the  yellow 
yelk,  forming  with  it  alternate  layers. 

Except  that  the  central  shining  opacity  of  the  pellucid  area  has  dis- 
appeared, that  the  size  of  the  area  has  increased,  and  that  the  opaque 
area  has  also  increased,  no  other  change  can  be  remarked  up  to  the  for- 
mation of  the  two  complete  layers.  There  is,  however,  a  slight  ill-de- 
fined opacity  at  the  posterior  part  of  the  area  pellucida,  known  as  the 
embryonic  shield.  This  opacity  is  probably  due  to  the  intermediate 
cells  already  mentioned  as  existing  betweeu  the  ejnblast  and  hypoblast. 


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HANDBOOK    OF   PHYSIOLOGY. 


In  the  posterior  part  of  the  area  pellucida  now  appears  an  opaque 
streak  which  extends  about  a  third  of  the  diameter  of  the  area  towards 
the  middle  line.  This  is  the  Primitive  streak.  It  is  found  on  trans- 
verse section  of  the  blastoderm  in  this  neighborhood  to  be  due  to  a  pro- 
liferation downwards  of  cells,  two  or  more  deep,  from  the  epiblast.     The 


Fig.  444.— Impregnated  egg,  with  commencement  of  formation  of  embryo;   showing  the  area 
germinativa  or  embryonic  spot,  the  area  pellucida,  and  the  primitive  groove  or  trace  (Dalton) . 

area  pellucida  now  becomes  oval.     As  the  primitive  streak  becomes  more 
defined,  the  area  pellucida  changes  its  oval  for  a  pear  shape,  but  the 


Fig.  445.— Transverse  section  through  embryo  chick  (26  hours),  a,  epiblast;  6,  mesoblast;  c, 
hypoblast;  d,  central  portion  of  mesoblast,  which  is  here  fused  with  epiblast;  e,  primitive  groove; 
/,  dorsal  ridge  (Klein). 

streak  increases  in  size  faster  than  the  area,  and  so  after  a  time  is  about 
two-thirds  of  its  length.     In  the  axis  of  the  primitive  streak  a  groove, 


Fig.  446.— Diagram  of  transverse  section  through  an  embryo  before  the  closing-in  of  the  medul- 
lary groove,  m,  cells  of  epiblast  lining  the  medullary  groove  which  will  form  the  spinal  cord;  h, 
epiblast;  d,  hypoblast;  ch,  notochord;  u,  proto  vertebra;  sp,  mesoblast;  w,  edge  of  lamina  dorsalis, 
folding  over  medullary  groove  (Kollikerj. 

the  primitive  groove,  runs.     From  the  primitive  streak  the  cells  from 
the  under-surface  of  the  epiblast  now  extend  as  lateral  wings  to  the  edge 


DEVELOPMENT. 


663 


of  the  pellucid  area;  they  are  not  joined  with  the  hypoblast.  The  inter- 
mediate layer  of  cells  in  this  position  producing  the  primitive  streak  is  a 
portion  of  the  intermediate  layer  or  mesoblast.  It  is  formed  chiefly 
from  the  epiblast,  but  laterally,  especially  in  the  front  part  of  the  primi- 
tive streak,  it  appears  to  be  derived  at  any  rate  in  part  from  the  cells  of 
the  primitive  lower  layer.  At  the  most  anterior  part  of  the  primitive 
streak,  at  the  point  which  corresponds  to  the  future  posterior  end  of  the 
embryo,  the  three  layers  are  all  joined  together. 

The  next  important  change  which  occurs  is  found  in  the  hypoblast  in 
front  of  the  primitive  streak.  The  irregular  layer  of  primitive  cells  of 
which  it  is  composed,  split  into  two  layers,  the  lower  of  flattened  cells 


Fir;.  447.— Portion  of  the  germinal  membrane,  with  rudiments  of  the  embryo;  from  the  ovum 
i  if  a  bitch.  The  primitive  groove,  a,  is  not  yet  closed,  and  at  its  upper  or  cephalic  end  presents 
three  dilatations,  n,  which  correspond  to  the  three  divisions  or  vesicles  of  the  brain.  At  its  lower 
extremity  the  groove  presents  a  lancet-shaped  dilatation  (sinus  rhomboidalis)  c.  The  margins  of 
the  groove  consist  of  clear  pellucid  nerve-substance.  Along  the  bottom  of  the  groove  is  observed  a 
faint-streak,  which  is  probably  the  chorda  dorsalis.    d,  Vertebral  plates  cBischoff). 

which  forms  the  hypoblast  proper,  and  an  upper  of  several   layers   of 
stellate  cells,  the  mesoblast. 

In  the  preceding  account  of  the  formation  of  the  blastodermic  layers, 
Balfour's  description  has  been  chiefly  followed.  It  differs  somewhat 
from  that  which  has  been  given  in  previous  editions  of  this  book.  The 
mesoblast  was  described  as  arising  from  the  hypoblast,  together  with 
some  of  the  large  formative  cells,  which  migrate  by  amoeboid  movement 
round  the  edge  of  the  hypoblast  (Fig.  488.  M),  and  no  difference  was 
made  in  the  formation  of  the 'mesoblast  in  the  primitive  streak  and  else- 
where. 

Now  appears  in  the  middle  line  extending  forwards  from  the  primitive 


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HANDBOOK    OF    PHYSIOLOGY. 


streak  an  opaque  line,  which  proceeds  almost  to  the  anterior  edge  of  the 
area  pellucida,  stopping  short  at  a  transverse  crescent-shaped  line,  the 
future  headfold.  This  line  is  the  commencing  notochord.  It  is  a  col- 
lection of  mesoblastic  cells  from  the  hypoblast  in  the  middle  line,  and 
remains  connected  with  the  latter  after  the  lateral  portions  of  the  meso- 
blast  have  become  quite  detached  from  it.  The  notochord  and  the  hypo- 
blast from  which  it  arises  are  continued  posteriorly  into  the  primitive 
streak.  Thus  the  mesoblast  of  the  area  on  either  side  of  the  middle  line 
in  which  the  embryo  is  formed  arises  from  the  hypoblast,  as  does  also 
the  notochord.  In  the  formation  of  the  medullary  plate  which  now 
appears,  the  epiblast  is  concerned.  In  the  middle  line  above  the  collec- 
tion of  cells  that  will  become  the  notochord  that  layer  becomes  thickened. 
The  sides  of  the  central  thickened  portion  are  elevated  somewhat  to  form 
the  medullary  folds,  inclosing  between  them  the  medullary  groove. 
Prom  this  medullary  plate  is  formed  the  central  nervous  system.  Al- 
though behind  the  groove  is  a  shallow  one,  if  it  be  traced  forwards  it 
becomes  deeper  and  narrower,  and  at  the  headfold  the  folds  curve  round 


Fig.  448.— Vertical  section  of  blastoderm  of  chick  (1st  day  of  incubation).  8,  epiblast,  consist- 
ing of  short  columnar  cells;  D,  hypoblast,  consisting  of  a  single  layer  of  flattened  cells;  M,  '-for- 
mative cells."  They  are  seen  on  the  right  of  the  figure,  passing  in  between  the  epiblast  and  hypo- 
blast to  form  the  mesoblast;  A,  white  yelk  granules.  Many  of  the  large."  formative  cells  "  are  seen 
containing  these  granules  (Strieker). 

and  meet  in  the  middle  line.  Anterior  to  the  headfold  is  a  second  fold 
parallel  to  it,  which  is  the  commencing  amnion. 

The  medullary  canal  is  bounded  by  its  two  folds  or  longitudinal  eleva- 
tions, laminae  dorsales,  which  are  folds  consisting  entirely  of  cells  of 
the  epiblast:  these  grow  up  and  arch  over  the  medullary  groove  (Fig. 
446)  till  after  some  time  they  coalesce  in  the  middle  line,  converting  it 
from  an  open  furrow  into  a  closed  tube— the  neural  canal  or  the  primi- 
tive cerebro-spinal  axis.  Over  this  closed  tube,  the  walls  of  which  con- 
sist of  more  or  less  cylindrical  cells,  the  superficial  layer  of  the  epiblast 
is  now  continued  as  a  distinct  membrane. 

The  union  of  the  medullary  folds,  or  laminae  dorsales  takes  place  first 
about  the  neck  of  the  future  embryo;  they  soon  after  unite  over  the  re- 
gion of  the  head,  while  the  closing  in  of  the  groove  progresses  much  more 
slowly  towards  the  hinder  extremity  of  the  embryo.  The  medullary 
groove  is  by  no  means  of  uniform  diameter  throughout,  but  even  before 
the  dorsal  lamina?  have  united  over  it,  is  seen  to  be  dilated  at  the  anterior 


DEVELOPMENT. 


G65 


extremity  and  obscurely  divided  by  constrictions  into  the  three  primary 
vesicles  of  the  bruin. 

The  part  from  which  the  spinal  cord  is  formed  is  of  nearly  uniform 
calibre,  while  towards  the  posterior  extremity  is  a  lozenge-shaped  dila- 
tation, sinus  rhomboidalis,  which  is  the  last  part  to  close  in  (Fig. 
447). 

Whilst  the  changes  which  have  been  described  are  taking  place  in  the 
area  pellucida,  which  has  enlarged  to  a  certain  exteut,  the  area  opaca 
has  considerably  extended.  The  hypoblast  and  mesoblast  have  also 
been  prolonged  laterally,  not  by  mere  extension,  but  also  from  the  ger- 


jm  ef 


Fig.  449.— Embryo  chick  (36  hours),  viewed  from  beueath  as  a  transparent  object  (magnified  >. 
pi,  outline  of  pellucid  area;  FB,  fore-brain,  or  first  cerebral  vesicle:  from  its  side  project  op,  the 
optic  vesicles;  SO,  backward  limit  of  somatopleure  fold.  "  tucked  in  "  under  bead;  a,  head-fold  of 
true  amnion;  a',  reflected  layer  of  amnion,  sometimes  termed  "  fivlse  amnion;"'  sp,  backward  limit 
of  splanchnopleure  folds,  alon#  which  run  the  omphalomesaraie  veins  uniting  to  form  /;,  the  heart, 
which  is  continued  forwards  into  bo,  the  bulbils  arteriosus,  d,  the  fore-eut  lying  behind  the  heart. 
and  having  a  wide  crescentic  opening  between  the  splanchnopleure  folds;  //A',  hind-brain:  MB, 
midbrain;  pv,  protovertebrae  lying  behind  the  fore-gut:  nic  liue'of  junction  of  medullary  folds  and 
Of  notochord;  ch,  front  end  of  notochord;  vpl,  vertebral  plates;  pr,  the  primitive-groove  at  its  cau- 
dal end  (Foster  and  Balfour). 


minal  wall,  which  is  the  thickened  edge  of  the  blastoderm,  together  with 
formative  cells  of  the  yelk;  on  each  side  of  the  notochord  and  medullary 
canal,  the  mesoblast  remains  as  a  longitudinal  thickening. 

It  now  however  splits  horizontally  into  two  layers  or  lamina?  (parietal 
and  visceral) :  of  these  the  former,  when  traced  out  from  the  central 
axis,  is  seen  to  be  in  close  apposition,  with  the  epiblast  and  gives  origin 


6V6 


HANDBOOK    OF    PHYSIOLOGY. 


to  the  parietes  of  the  trunk,  while  the  latter  adheres  more  or  less  closely 
to  the  hypoblast,  and  gives  rise  to  the  serous  and  muscular  walls  of  the 
alimentary  canal  and  several  other  parts  (Fig.  450). 

The  united  parietal  layer  of  the  mesoblast  with  the  epiblast  is  termed 
Somatopleure,  the  united  visceral  layer  and  hypoblast,  Splanchno- 
pleure.  The  space  between  them  is  the  pleuro-peritoneal  cavity, 
which  becomes  subdivided  by  subsequent  partitions  into  pericardium, 
pleura,  and  peritoneum. 


Mc 


J>2 


£J* 


■CC9 


Fig.  450. — Transverse  section  through  dorsal  region  of  embryo  chick  (45  hrs.).  One-half  of 
the  section  is  represented:  if  completed  it  would  extend  as  far  to  the  left  as  to  the  right  of  the  line 
of  the  medullary  canal  (A/c).  A,  epiblast;  C,  hypoblast,  consisting  of  a  single  layer  of  flattened 
cells;  Mc,  medullary  canal;  Pv,  protovertebra;  Wd,  Wolffian  duct:  So,  somatapleure ;  Sp,  splanch- 
nopleure;  pp,  pleuro-peritoneal  cavity;  ch,  notochord;  ao,  dorsal  aorta,  containing  blood-cells;  v, 
blood-vessels  of  the  yolk-sac  (Foster  and  Balfour). 

The  splitting  of  the  mesoblast  extends  almost  to  the  medullary  canal, 
but  a  portion  on  either  side  ( p.  v.  Fig.  450)  remains  undivided,  the 
vertebral  plate.  The  divided  portion  is  known  as  the  lateral  plate. 
The  longitudinal  thickening  of  the  vertebral  plate  is  seen  after  awhile 
to  be  divided,  at  right  angles  to  the  medullary  canal  by  bright  trans- 


tfi? 


Fig.  451.— Diagrammatic  longitudinal  section  through  the  axis  of  an  embryo.  The  head-fold 
has  commenced,  but  the  tail-fold  has  not  yet  appeared;  FSo,  fold  of  the  somatopleure;  FSp,  fold 
of  the  splanchnopleure;  the  line  of  reference,  FSo,  lies  outside  the  embryo  in  the  "moat,"  -which 
marks  off  the  overhanging  head  from  the  amnion ;  D,  inside  the  embryo,  is  that  part  which  is  to 
become  the  fore-gut;  FSo  and  Fsp,  are  both  parts  of  the  head-fold,  and  travel  to  the  left  of  the 
figure  as  development  proceeds;  pp,  space  between  somatopleure  and  splanchnopleure,  pleuro-peri- 
toneal cavity:  Am,  commencing  head-fold  of  amnion;  NC,  neural  canal;  Ch,  notochord;  Ht,  heart; 
A,  B,  C,  epiblast,  mesoblast,  hypoblast  (Foster  and  Balfourj. 

verse  lines  into  a  number  of  square  segments.  These  segments,  which 
are  the  surface  appearance  of  cubes  of  mesoblast,  are  the  mesoblastic 
somites  or  protovertebrae.  The  first  three  or  four  of  these  proto- 
vertebrae  make  their  appearance  in  the  cervical  region,  while  one  or  two 


DEVELOPMENT. 


667 


more  are  formed  in  front  of  this  point;  and  the  series  is  continued  back- 
ward till  the  whole  medullary  canal  is  flanked  by  them  (Fig.  449).  That 
which  is  first  formed  corresponds  to  the  second  cervical  vertebrae.  From 
these  somites  the  vertebrae  and  the  trunk  muscles  are  derived. 

Head  and  Tail  Folds.  Body  Cavity. — Every  vertebrate  animal 
consists  essentially  of  a  longitudinal  axis  (vertebral  column)  with  a 
neural  canal  above  it,  and  a  body-cavity  (containing  the  alimentary 
canal)  beneath. 

We  have  seen  how  the  earliest  rudiments  of  the  central  axis  and  the 
neural  canal  are  formed;  we  must  now  consider  how  the  general  body- 
cavity  is  developed.     In  the  earliest  stages  the  embryo  lies  flat  on  the 


Fig.  452.— Diagrammatic  section  showing  the  relation  in  a  mammal  between  the  primitive  alimen- 
tary canal  and  the  membranes  of  the  ovum.  The  stage  represented  in  this  diagram  corresponds  to 
that  of  the  fifteenth  or  seventeenth  day  in  the  human  embryo,  previous  to  the  expansion  of  the 
altantois;  c,  the  villous  chorion ;  a,  the  amnion;  a',  the  place  or  convergence  of  the  amnion  and 
reflexion  of  the  false  amnion,  a"  a",  or  outer  or  corneous  layer;  e,  the  head  and  trunk  of  the 
embryo,  comprising  the  primitive  vertebrae  and  cere bro-spinal  axis;  i,  i,  the  simple  alimentary 
'•anal  in  its  upper  and  lower  portions.  Immediately  beneath  the  riRht  band  i  is  seen  the  total 
heart,  lying  in  the  anterior  part  of  the  pleuro-peritoneal  cavity;  v,  the  yolk-sac  or  umbilical  vesicle: 
!•/,  the  vitello-intestinal  opening;  u,  the  allantois  connected  by  a  pedicle  with  the  anal  portion  of 
the  alimentary  canal  (Quain'. 

surface  of  the  yelk,  and  is  not  clearly  marked  off  from  the  rest  of  the 
blastoderm:  but  gradually  the  head-fold  or  crescentic  depression  (with 
its  concavity  backwards)  is  formed  in  the  blastoderm,  limiting  the  head 
of  the  embryo;  the  blastoderm  is,  as  it  were,  tucked  in  under  the  head, 
which  thus  comes  to  project  above  the  general  surface  of  tlw  membrane: 
a  similar  tucking  in  of  blastoderm  takes  place  at  the  caudal  extremity, 
and  thus  the  head  and  tail  folds  are  formed  (Fig.  452). 

Similar  depressions  mark  off  the  embryo  laterally,  until   it  is  com- 


668  HANDBOOK    OF    PHYSIOLOGY. 

pletely  surrounded  by  a  sort  of  moat  which  it  overhangs  on  all  sides,  and 
which  clearly  defines  it  from  the  yelk. 

This  moat  runs  in  further  and  further  all  round  beneath  the  over- 
hanging embryo,  till  the  latter  comes  to  resemble  a  canoe  turned  upside- 
down,  the  ends  and  middle  being,  as  it  were,  decked  in  by  the  folding 
or  tucking  in  of  the  blastoderm,  while  on  the  ventral  surface  there  is 
still  a  large  communication  with  the  yelk,  corresponding  to  the  well  or 
undecked  portion  of  the  canoe. 

This  communication  between  the  embryo  and  the  yelk  is  gradually 
contracted  by  the  further  tucking  in  of  the  blastoderm  from  all  sides, 
till  it  becomes  narrowed  down,  as  by  an  invisible  constricting  band,  to  a 
mere  pedicle  which  passes  out  of  the  body  of  the  embryo  at  the  point  of 
the  future  umbilicus. 

The  downwardly  folded  portions  of  blastoderm  are  termed  the  vis- 
ceral plates. 

Thus  we  see  that  the  body-cavity  is  formed  by  the  downward  folding 
of  the  visceral  plates,  just  as  the  neural  cavity  is  produced  by  the  up- 
ward growth  of  the  dorsal  laminse,  the  difference  being  that,  in  the 
visceral  or  ventral  laminas,  all  three  layers  of  the  blastoderm  are  con- 
cerned. 

The  folding  in  of  the  splanchnopleure,  lined  by  hypoblast,  pinches 
off,  as  it  were,  a  portion  of  the  yelk-sac,  inclosing  it  in  the  body-cavity. 
This  forms  the  rudiment  of  the  alimentary  canal,  which  at  this  period 
ends  blindly  towards  the  head  and  tail,  while  in  the  centre  it  communi- 
cates freely  with  the  cavity  of  the  yelk-sac  through  the- canal  termed 
vitelline  or  omphalo-mesenteric  duct. 

The  yelk-sac  thus  becomes  divided  into  two  portions  which  communi- 
cate through  the  vitelline  duct,  that  portion  within  the  body  giving  rise, 
as  above  stated,  to  the  digestive  canal,  and  that  outside  the  body  remain- 
ing for  some  time  as  the  umbilical  vesicle  (Fig.  453,  ys).  The  hypoblast 
forming  the  epithelium  of  the  intestine  is  of  course  continuous  with  the 
lining  membrane  of  the  umbilical  vesicle,  while  the  visceral  plate  of  the 
mesoblast  is  continuous  with  the  outer  layer  of  the  umbilical  vesicle. 

All  the  above  details  will  be  clear  on  reference  to  the  accompanying 
-diagrams. 

At  the  posterior  end  of  the  embryo  chick,  when  the  amniotic  fold  is 
commencing  to  be  formed,  and  the  hind  fold  of  the  splanchnopleure  has 
commenced,  there  remains  for  a  time  a  communication  between  the 
neural  canal  and  the  hind  gut,  which  is  called  the  neurenteric  canal. 
It  passes  in  at  the  point  where  the  notochord  falls  into  the  primitive 
streak.  The  anterior  part  of  the  primitive  streak  becomes  the  tail  swell- 
ing, the  posterior  part  atrophies,  and  the  corresponding  lateral  part  of 
the  blastoderm  forms  part  of  the  body-wall  of  the  embryo.  The  ante- 
rior part  of  the  medullary  canal  having  been  completely  roofed  in;  the 


DEVELOPMENT.  669 

foremost  portion  undergoes  dilatation,  and  a  bulb,  or  first  cerebral 
vesicle  results.  From  either  side  of  this  dilatation  a  process,  the  cavity 
of  which  is  in  communication  with  it,  is  separated  off;  these  processes 
are  the  optic  vesicles.  Behind  the  first  cerebral  vesicle  two  other  vesicles 
now  arise,  and  at  the  posterior  part  of  the  head  two  small  pits,  the  au- 
ditory pits,  are  to  be  seen.  The  folding  of  the  head,  it  should  be  rec- 
ollected, is  the  cause  of  the  inclosure  below  the  neural  canal  (Fig.  451) 
of  a  canal  ending  blindly,  which  has  in  front  the  splanchnopleure,  and 
which  is  just  as  long  as  the  involution  of  that  membrane.  This  canal 
is  the  fore-gut.  In  the  interior  of  the  splanchnopleure  fold  below  it 
(as  seen  in  Fig.  451)  in  the  pleuro-peritoneal  cavity  the  heart  is  formed, 
at  the  point  where  the  splanchnopleure  makes  its  turn  forwards.  It 
arises  as  a  thickening  of  the  mesoblast  on  either  side  as  the  two  splanch- 
nopleure folds  diverge,  and  of  a  thickening  of  the  mesoblast  at  the  point 
of  divergence.  So  that  at  first  the  rudiment  of  the  heart  is  like  an  in- 
verted V,  which  by  the  gradual  coming  together  of  the  diverging  cords  is 
converted  into  an  inverted  Y. 

The  cylinders  become  hollowed  out,  and  are  thus  converted  into  tubes, 
which  then  coalesce.  Layers  are  separated  off  towards  the  interior, 
which  become  the  epithelial  lining,  and  the  mass  of  the  mesoblast  sur- 
rounding this  afterwards  forms  the  muscle  and  serous  covering,  whilst  at 
first  the  rudimentary  organ  is  attached  to  the  gut  by  a  mesoblastic  mesen- 
tery, the  mesocardium. 

Fcetal  Membranes. 

Umbilical  Vesicle  or  Yelk-sac. — The  splanchnopleure,  lined  by 
hypoblast,  forms  the  yelk-sac  in  Reptiles,  Birds,  and  Mammals;  but  in 
Amphibia  and  Fishes,  since  there  is  neither  amnion  nor  allantois,  the 
wall  of  the  yelk-sac  consists  of  all  three  layers  of  the  blastoderm,  inclosed, 
of  course,  by  the  original  vitelline  membrane. 

The  body  of  the  embryo  becomes  in  great  measure  detached  from  the 
yelk  sac  or  umbilical  vesicle,  which  contains,  however,  the  greater  part 
of  the  substance  of  the  yelk,  and  furnishes  a  source  whence  nutriment 
is  derived  for  the  embryo.  This  nutriment  is  absorbed  by  the  numerous 
vessels  (omphalo-mesenteric)  which  ramify  in  the  walls  of  the  yelk-sac, 
forming  what  in  birds  is  termed  the  area  vasculosa.  In  Birds,  the 
contents  of  the  yelk-sac  afford  nourishment  until  the  end  of  incubation, 
and  the  omphalo-mesenteric  vessels  are  developed  to  a  corresponding 
degree;  but  in  Mammalia  the  office  of  the  umbilical  vesicle  ceases  at  a 
very  early  period,  the  quantity  of  the  yelk  is  small,  and  the  embryo  soon 
becomes  independent  of  it  by  the  connections  it  forms  with  the  parent. 
Moreover,  in  Birds,  as  the  sac  is  emptied,  it  is  gradually  drawn  into  the 
abdomen  through  the  umbilical  opening,  which  then  closes  over  it:  but 
in  Mammalia  it  always  remains  on  the  outside;  and  as  it  is  emptied  it 


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contracts  (Fig.  455),  shrivels  up,  and  together  with  the  part  of  its  duct 
external  to  the  abdomen,  is  detached  and  disappears  either  before  or  at 
the  termination  of  intra-uterine  life,  the  period  of  its  disappearance 
varying  in  different  orders  of  Mammalia. 

AYhen  blood-vessels  begin  to  be  developed,  they  ramify  largely  over 
the  walls  of  the  umbilical  vesicle,  and  are  actively  concerned  in  absorb- 
ing its  contents  and  conveying  them  away  for  the  nutrition  of  the  em- 
bryo. 


Fig.  453. — Diagrams  showing  three  successive  stages  of  development.  Transverse  vertical  sec- 
tions. The  yelk-sac,  ys,  is  seen  progressively  diminishing  in  size.  In  the  embryo  itself  the  medul- 
lary canal  and  notochord  are  seen  in  section.  a',  in  middle  figure,  the  alimentary  canal,  becoming 
pinched  off,  as  it  were,  from  the  yelk-sac;  a',  in  right  hand  figure,  alimentary  canal  completely 
closed;  a,  in  last  two  figures,  amnion;  ac,  cavity  of  amnium  filled  with  amniotic  fluid;  pp,  space 
between  amnion  and  chorion  continuous  with  the  pleuro-peritoneal  cavity  inside  the  body;  vt, 
vitelline  membrane;  ys,  yelk-sac,  or  umbilical  vesicle  (Foster  and  Balfour). 

At  an  early  stage  of  development  of  the  foetus,  and  some  time  before 
the  completion  of  the  changes  which  have  been  just  described,  two  im- 


Fig.  454. 


Fig.  455. 
a,  area  pellucida;  b,   area  vasculosa; 


Fig.  454. — Diagram  showing  vascular  area  in  the  chick, 
c,  area  vitellina. 

Fig.  455.— Human  embryo  of  fifth  week  with  umbilical  vesicle;  about  natm-al  size   (Dalton). 
The  human  umbilical  vesicle  never  exceeds  the  size  of  a  small  pea. 

portant  structures,  called  respectively  the  amnion  and  the  allantois, 
begin  to  be  formed. 

Amnion. — The  amnion  is  produced  as  follows: — Beyond  the  head- 
and  tail-folds  before  described  (p.  667),  the  somatopleure  coated  by  epi- 
blast,  is  raised  into  folds,  which  grow  up,  arching  over  the  embryo,  not 
only  anteriorly  and  posteriorly  but  also  laterally,  and   all  converging 


DEVELOPMENT.  ft  71 

towards  one  point  over  its  dorsal  surface  (Fig.  453).  The  growing  up 
of  these  folds  from  all  sides  and  their  convergence  towards  one  point 
very  closely  resembles  the  folding  inwards  of  the  visceral  plates  already 
described,  and  hence,  by  some,  the  point  at  which  the  amniotic  folds 
meet  over  the  back  has  been  termed  the  amniotic  umbilicus. 

The  folds  not  only  come  into  contact  but  coalesce.  The  inner  of  the 
two  layers  forms  the  true  amnion,  while  the  outer  or  reflected  layer, 
sometimes  termed  the  false  amnion,  coalesces  with  the  inner  surface  of 
the  original  vitelline  membrane  to  form  the  subzonal  membrane  or 
false  chorion.  This  growth  of  the  amniotic  folds  must  of  course  be 
clearly  distinguished  from  the  very  similar  process,  already  described 
by  which  the  walls  of  the  neural  canal  are  formed  at  a  much  earlier 
stage. 

The  cavity  between  the  true  amnion  and  the  external  surface  of  the 
embryo  becomes  a  closed  space,  termed  the  amniotic  cavity  (ac,  Fig. 
453). 

At  first,  the  amnion  closely  invests  the  embryo,  but  it  becomes 
gradually  distended  with  fluid  (liquor  amnii),  which,  as  pregnancy  ad- 
vances, reaches  a  considerable  quantity. 

This  fluid  consists  of  water  containing  small  quantities  of  albumen 
and  urea.  Its  chief  function  during  gestation  appears  to  be  the  mechan- 
ical one  of  affording  equal  support  to  the  embryo  on  all  sides,  aud  of 
protecting  it  as  far  as  possible  from  the  effects  of  blows  and  other  inju- 
ries to  the  abdomen  of  the  mother. 

The  embryo  up  to  the  end  of  pregnancy  is  thus  immersed  in  fluid, 
which  during  parturition  serves  the  important  purpose  of  gradually  and 
evenly  dilating  the  neck  of  the  uterus  to  allow  of  the  passage  of  the  foe- 
tus: when  this  is  accomplished  the  amniotic  sac  bursts,  and  the  "  waters  " 
escape. 

On  referring  to  the  diagrams  (Fig.  453),  it  will  be  obvious  that  the 
cavity  outside  the  amnion  (between  it  and  the  false  amnion)  is  continu- 
ous with  the  pleuro-peritoneal  cavity  at  the  umbilicus.  This  cavity  is 
not  entirely  obliterated  even  at  birth,  and  contains  a  small  quantity  of 
fluid  (" false  waters"),  which  is  discharged  during  parturition  either 
before,  or  at  the  same  time  as  the  amniotic  fluid. 

Allantois. — Into  the  pleuro-peritoneal  space  the  allantois  sprouts 
out,  its  formation  commencing  during  the  development  of  the  amnion. 

Growing  out  from  or  near  the  hinder  portion  of  the  intestinal  canal 
(c,  Fig.  456),  with  which  it  communicates,  the  allantois  is  at  first  a  solid 
pear-shaped  mass  of  splanchnopleure;  but  becoming  vesicular  by  the 
projection  into  it  of  a  hollow  out-growth  of  hypoblast,  and  very  soon 
simply  membranous  and  vascular,  it  insinuates  itself  between  the  amni- 
otic folds,  just  described,  and  comes  into  close  contact  and  union  with 
the  outer  of  the  two  folds,  which  has  itself,  as  before  said,  become  one 


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with  the  external  investing  membrane  of  the  egg.  As  it  grows,  the 
allantois  develops  muscular  tissue  in  its  external  wall  and  becomes  ex- 
ceedingly vascular;  in  birds  (Fig.  457)  it  envelops  the  whole  embryo — 
taking  up  vessels,  so  to  speak,  to  the  outer  investing  membrane  of  the 
egg,  and  lining  the  inner  surface  of  the  shell  with  avascular  membrane, 
by  these  means  affording  an  extensive  surface  in  which  the  blood  may  be 
aerated.  In  the  human  subject  and  other  Mammalia,  the  vessels  carried 
out  by  the  allantois  are  distributed  only  to  a  special  part  of  the  outer 
membrane  or  false  chorion,  where,  by  interlacement  with  the  vascular 
system  of  the  mother,  a  structure  called  the  placenta  is  developed. 

In  Mammalia,  as  the  visceral  laminae  close  in  the  abdominal  cavity, 
the  allantois  is  thereby  divided  at  the  umbilicus  into  two  portions;  the 
outer  part,  extending  from  the  umbilicus  to  the  chorion,  soon  shrivelling; 
while  the  inner  part,  remaining  in  the  abdomen,  is  in  part  converted 
into  the  urinary  bladder;  the  portion  of  the  inner  part  not  so  converted, 
extending  from  the  bladder  to  the  umbilicus,  under  the  name  of  the 
urachus.     After  birth  the  umbilical  cord,  and  with  it  the  external  and 


Fig.  456. 


Fig.  457. 


Fig.  456. — Diagram  of  fecundated  egg.  a,  umbilical  vesicle;  b,  amniotic  cavity;  c,  allantois. 
(Dalton.) 

Fig.  457. — Fecundated  egg  with  allantois  nearly  complete,  a,  inner  layer  of  amniotic  fold ;  6, 
outer  layer  of  ditto;  c,  point  where  the  amniotic  folds  come  in  contact.  The  allantois  is  seen  pene- 
trating between  the  outer  and  inner  layers  of  the  amniotic  folds.  This  figure,  which  represents 
only  the  amniotic  folds  and  the  parts  within  them,  should  be  compared  with  Figs,  453,  459,  in  which 
will  be  found  the  structures  external  to  these  folds.    (Dalton.) 


shrivelled  portion  of  the  allantois,  are  cast  off  at  the  umbilicus,  while 
the  urachus  remains  as  an  impervious  cord  stretched  from  the  top  of  the 
urinary  bladder  to  the  umbilicus,  in  the  middle  line  of  the  body,  imme- 
diately beneath  the  parietal  layer  of  the  peritoneum.  It  is  sometimes 
enumerated  among  the  ligaments  of  the  bladder. 

It  must  not  be  supposed  that  the  phenomena  which  have  been  suc- 
cessively described,  occur  in  any  regular  order  one  after  another.  On 
the  contrary,  the  development  of  one  part  is  going  on  side  by  side  with 
that  of  anotber. 

The  Chorion. — It  has  been  already  remarked  that  the  allantois  is  a 
structure  which  extends  from  the  body  of  the  f cetus  to  the  outer  investing 
membrane  of  the  ovum,  that  it  insinuates  itself  between  the  two  layers 
of  the  amniotic  fold,  and  becomes  fused  with  the  outer  layer,  wbich  has 


DEVELOPMENT. 


673 


itself  become  previously  fused  with  the  vitelline  membrane.  By  these 
means  the  external  investing  membrane  of  the  ovum,  or  the  true  chorion, 
as  it  is  now  called,  represents  three  layers,  namely,  the  original  vitelline 
membrane,  the  outer  layer  of  the  amniotic  fold,  and  the  allantois. 

Very  soon  after  the  entrance  of  the  ovum  into  the  uterus,  in  the 
human  subject,  the  outer  surface  of  the  chorion  is  found  beset  with 
fine  processes,  the  so-called  villi  of  the  chorion  (a,  Figs.  458,  459), 
which  give  it  a  rough  and  shaggy  appearance.  At  first  only  cellular 
in  structure,  these  little  outgrowths  subsequently  become  vascular  by 
the  development  in  them  of  loops  of  capillaries  (Fig.  4G0);  and  the  latter 
at  length  form  the  minute  extremities  of  the  blood-vessels  which  are,  so 
to  speak,  conducted  from  the  foetus  to  the  chorion  by  the  allantois. 
The  function  of  the  villi  of  the  chorion  is  evidently  the  absorption  of 
nutrient  matter  for  the  foetus;  and  this  is  probably  supplied  to  them  at 
first  from  the  fluid  matter,  secreted  by  the  follicular  glands  of  the  uterus, 


Figs.  458  and  459. -a,  chorion  with  villi  The  villi  are  shown  to  be  best  developed  in  the 
part  of  the  chorion  to  which  the  allantois  is  extending;  this  portion  ultimately  becomes  the  pla 
cento;  b,  space  between  the  two  layers  of  the  amnion;  c,  amniotic  cavity;  d,  situation  of  the  intes- 
tine, showing  its  connection  with  the  umbilical  vesicle;  e,  umbilical  vesicle;/,  situation  of  heart 
and  vessels;  </,  allantois. 

in  which  they  are  soaked.  Soon,  however,  the  foetal  vessels  of  the  villi 
come  into  more  intimate  relation  with  the  vessels  of  the  uterus.  The 
part  at  which  this  relation  between  the  vessels  of  the  foetus  and  those  of 
the  parent  ensues,  is  not,  however,  over  the  whole  surface  of  the  chorion: 
for,  although  all  the  villi  become  vascular,  yet  they  become  indistinct  or 
disappear  except  at  one  part  where  they  are  greatly  developed,  and  by 
their  branching  give  rise,  with  the  vessels  of  the  uterus,  to  the  formation 
of  the  placenta. 

To  understand  the  manner  in  which  the  fatal  and  maternal  blood- 
vessels come  into  relation  with  each  other  in  the  placenta,  it  is  necessary 
briefly  to  notice  the  changes  which  the  uterus  undergoes  after  impregna- 
tion. These  changes  consist  especially  of  alterations  in  structure  of  the 
superficial  part  of  the  mucous  membrane  which  lines  the  interior  of  the 
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uterus,  and  which  forms,  after  a  kind  of  development  to  be  immediately 
described,  the  membrana  decidua,  so  called  on  account  of  its  being  dis- 
charged from  the  uterus  at  birth. 

Formation  of  the  Placenta. 

The  mucous  membrane  of  the  human  uterus,  which  consists  of  a 
matrix  of  connective  tissue  containing  numerous  corpuscles  (adenoid 
tissue),  and  is  lined  internally  by  columnar  ciliated  epithelium,  is  abun- 
dantly beset  with  tubular  glands,  arranged  perpendicularly  to  the  sur- 
face (Fig.  461).  These  follicles  are  very  small  in  the  unimpregnated 
uterus,  but  when  examined  shortly  after  impregnation,  they  are  found 
elongated,  enlarged,  and  much  waved  and  contorted  towards  their  deep 
and  closed  extremity,  which  is  implanted  at  some  depth  in  the  tissue  of 
the  uterus,  and  may  dilate  into  two  or  three  closed  sacculi  (Fig.  461). 


Fig.  460. 


Fig.  461. 


Fig.  461.— Section  of  the  lining  membrane  of  a  human  uterus  at  the  period  of  commencing  preg- 
nancy showing  the  arrangement  and  other  peculiarities  of  the  glands,  d,  d,  d,  with  their  orifices, 
a,  a,  a,  on  the  internal  surface  of  the  organ.    Twice  the  natural  size. 

The  glands  are  lined  by  columnar  ciliated  epithelium,  and  they  open 
on  the  inner  surface  of  the  mucous  membrane  by  small  round  orifices  set 
closely  together  (a,  a,  Fig.  461). 

On  the  internal  surface  of  the  mucous  membrane  may  be  seen  the 
circular  orifices  of  the  glands,  many  of  wbich  are,  in  the  early  period  of 
pregnancy,  surrounded  by  a  whitish  ring,  formed  of  the  epithelium  which 
lines  the  follicles  (Fig.  462). 

Coincidently'with  the  occurrence  of  pregnancy,  important  changes 
occur  in  the  structure  of  the  mucous  membrane  of  the  uterus.  The 
epithelium  and  sub-epithelial  connective  tissue,  together  with  the  tubular 
glands,  increase  rapidly,  and  there  is  a  greatly  increased  vascularity  of 
the  whole  mucous  membrane,  the  vessels  of  the  mucous  membrane  be- 
coming larger  and  more  numerous;  while  a  substance  composed  chiefly 
of  nucleated  cells  fills  up  the  interfollicular  spaces  in  which  the  blood- 


DEVELOPMENT. 


6 


»•> 


vessels  are  contained.  The  effect  of  these  changes  is  an  increased 
thickness,  softness,  and  vascularity  of  the  mucous  membrane,  the  super- 
ficial part  of  which  itself  forms  the  membrana  decidua. 

The  object  of  this  increased  development  seems  to  be  the  production 
of  nutritive  materials  for  the  ovum;  for  the  cavity  of  the  uterus  shortly 
becomes  filled  with  secreted  fluid,  consisting  almost  entirely  of  nucleated 
cells  in  which  the  villi  of  the  chorion  are  imbedded. 

When  the  ovum  first  enters  the  uterus  it  becomes  imbedded  in  the 
structure  of  the  decidua,  which  is  yet  quite  soft,  and  in  which  soon 
afterwards  three  portions  are  distinguishable.  These  have  been  named 
the  decidua  vera,  the  decidua  reilexa,  and  the  decidua  serotina.  The 
first  of  these,  the  decidua  vera,  lines  the  cavity  of  the  uterus;  the  second, 
or  decidua  reilexa,  is  a  part  of  the  decidua  vera  which  grows  up  around 
the  ovum,  and,  wrapping  it  closely,  forms  its  immediate  investment. 


Fig.  402. 


Fig.  463. 


Fio.  462.— Two  thin  segments  of  human  decidua  after  recent  impregnation,  viewed  on  a  dark 
ground :  they  show  the  open  ings  on  the  surface  of  the  membrane,  a,  is  magnified  six  diameters,  and 
b,  twelve  diameters.  At  1,  the  lining  of  epithelium  is  seen  within  the  orifices,  at  2  it  has  escaped. 
(Sharpey.  i 

Fig.  463.— Diagram  of  an  early  stage  of  the  formation  of  the  human  placenta,  a,  embryo;  b, 
amnion;  c,  placental  vessels ;  d,  decidua  reflexa;  e,  allantois; /,  placental  villi;  g,  mucous  mem- 
brane.   CCadiat.) 

The  third,  or  decidua  serotina,  is  the  part  of  the  decidua  vera  which 
becomes  especially  developed  in  connection  with  those  villi  of  the 
chorion,  which,  instead  of  disappearing,  remain  to  form  the  fcetal  part 
of  the  placenta. 

In  connection  with  these  villous  processes  of  the  chorion,  there  arc 
developed  (lej)ressions  or  crypts  in  the  decidual  mucous  membrane,  which 
correspond  in  shape  with  the  villi  they  are  to  lodge;  and  thus  the  chori- 
onic villi  become  more  or  less  imbedded  in  the  maternal  structures. 
These  uterine  crypts,  it  is  important  to  note,  are  not,  as  was  once  sup- 
posed, merely  the  open  mouths  of  the  uterine  follicles. 

As  the  ovum  increases  in  size,  the  decidua  vera  and  the  decidua  reilexa 


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gradually  come  into  contact,  and  in  the  third  month  of  pregnancy  the 
cavity  between  them  has  quite  disappeared.  Henceforth  it  is  very  diffi- 
cult, or  even  impossible,  to  distinguish  the  two  layers. 

The  Placenta. — During  these  changes  the  deeper  part  of  the  mu- 
cous membrane  of  the  uterus,  at  and  near  the  region  where  the  placenta 
is  placed,  becomes  hollowed,  out  by  sinuses,  or  cavernous  spaces,  which 
communicate  on  the  one  hand  with  arteries  and  on  the  other  with  veins 
of  the  uterus.  Into  these  sinuses  the  villi  of  the  chorion  protrude,  push- 
ing the  thin  wall  of  the  sinus  before  them,  and  so  come  into  intimate 
relation  with  the  blood  contained  in  them.     There  is  no  direct  com- 


Fig.  464. 


Fig.  466. 


Fig.  464.— Diagrammatic  view  of  a  vertical  transverse  section  of  the  uterus  at  the  seventh  or 
eighth  week  of  pregnancy,  c,  c,  c',  cavity  of  the  uterus,  which  becomes  the  cavity  of  the  decidua, 
opening  at  c,  c,  the  cornua,  into  the  Fallopian  tubes,  and  at  c'  into  the  cavity  of  the  cervix,  which 
is  closed  by  a  plug  of  mucus;  d  v,  decidua  vera;  dr,  decidua  reflexa,  with  the  sparser  villi  im- 
bedded in  its  substance;  d  s,  decidua  serotina,  involving  the  more  developed  chorionic  villi  of  the 
commencing  placenta.  The  foetus  is  seen  lying  in  the  amniotic  sac;  passing  up  from  the  umbilicus 
is  seen  the  umbilical  cord  and  its  vessels,  passing  to  their  distribution  in  the  villi  of  the  chorion;  also 
the  pedicle  of  the  yelk  sac,  which  lies  in  the  cavity  between  the  amnion  and  chorion.  (Allen  Thom- 
son.) 

Fig.  465.  Extremity  of  a  placental  villus,  a,  lining  membrane  of  the  vascular  system  of  the 
mother;  b,  cells  immediately  lining  a;  d,  space  between  the  maternal  and  foetal  portions  of  the  vi- 
lus;  e,  internal  membrane  or  the  villus,  or  external  membrane  of  the  chorion;/,  internal  cells  of  the 
villus,  or  cells  of  the  chorion ;  g,  loop  of  umbilical  vessels.    ( Goodsir.) 

munication  between  the  blood-vessels  of  the  mother  and  those  of  the 
foetus;  but  the  layer  or  layers  of  membrane  intervening  between  the 
blood  of  the  one  and  of  the  other  offer  no  obstacle  to  a  free  interchange 
of  matters  between  them.   Thus  the  villi  of  the  chorion  containing  fcetal 


DEVELOPMENT.  677 

blood,  are  bathed  or  soaked  in  maternal  blood  contained  in  the  uterine 
sinuses.  The  arrangement  may  be  roughly  compared  to  filling  a  glove 
with  foetal  blood,  and  dipping  its  fingers  into  a  vessel  containing  mater- 
nal blood.  But  in  the  fcetal  villi  there  is  a  constant  stream  of  blood 
into  and  out  of  the  loop  of  capillary  blood-vessels  contained  in  it,  as  there 
is  also  into  and  out  of  the  maternal  sinuses. 

It  would  seem  that,  at  the  villi  of  the  placental  tufts,  where  the  fcetal 
and  maternal  portions  of  the  placenta  are  brought  into  close  relation 
with  each  other,  the  blood  in  the  vessels  of  the  mother  is  separated  from 
that  in  the  vessels  of  the  foetus  by  the  intervention  of  two  distinct  sets 
of  nucleated  cells  (Fig.  465).  One  of  these  (b)  belongs  to  the  maternal 
portion  of  the  placenta,  is  placed  between  the  membrane  of  the  villus 
and  that  of  the  vascular  system  of  the  mother,  and  is  probably  designed 
to  separate  from  the  blood  of  the  parent  the  materials  destined  for  the 
blood  of  the  foetus;  the  other  (/)  belongs  to  the  foetal  portion  of  the 
placenta,  is  situated  between  the  membrane  of  the  villus  and  the  loop  of 
vessels  contained  within,  and  probably  serves  for  the  absorption  of  the 
material  secreted  "by  the  other  sets  of  cells,  and  for  its  conveyance  into 
the  blood-vessels  of  the  foetus.  Between  the  two  sets  of  cells  with  their 
investing  membrane  there  exists  a  space  (d),  into  which  it  is  probable 
that  the  materials  secreted  by  the  one  set  of  cells  of  the  villus  are  poured 
in  order  that  they  may  be  absorbed  by  the  other  set,  and  thus  conveyed 
into  a  fcetal  vessel. 

Not  only,  however,  is  there  a  passage  of  materials  from  the  blood  of 
the  mother  into  that  of  the  foetus,  but  there  is  a  mutual  interchange  of 
materials  between  the  blood  both  of  foetus  and  of  parent;  the  latter  sup- 
plying the  former  with  nutriment,  and  in  turn  abstracting  from  it  ma- 
terials which  require  to  be  removed. 

Alexander  Harvey's  experiments  were  very  decisive  on  this  point.  The 
view  has  also  received  abundant  support  from  Hutchinson's  important 
observations  on  the  communication  of  syphilis  from  the  father  to  the 
mother,  through  the  instrumentality  of  the  foetus;  and  still  more  from 
Savory's  experimental  researches,  which  prove  quite  clearly  that  the 
female  parent  may  be  directly  inoculated  through  the  foetus.  Having 
opened  the  abdomen  and  uterus  of  a  pregnant  bitch.  Savory  injected  a 
solution  of  strychnia  into  the  abdominal  cavity  of  one  foetus,  and  into 
the  thoracic  cavity  of  another,  and  then  replaced  all  the  parts,  every 
precaution  being  taken  to  prevent  escape  of  the  poison.  In  less  than 
half  an  hour  the  bitch  died  from  tetanic  spasms;  the  fetuses  operated  on 
were  also  found  dead,  while  the  others  were  alive  and  active.  The  ex- 
periments, repeated  on  other  animals  with  like  results,  leave  no  doubt  of 
the  rapid  and  direct  transmission  of  matter  from  the  foetus  to  the  mother 
through  the  blood  of  the  placenta. 

The  placenta,  therefore,  of  the  human  subject  is  composed  of  afivful 
part  and  a  maternal  part, — the  term  placenta  properly  including  all  that 


678  HANDBOOK    OF   PHYSIOLOGY. 

entanglement  of  total  villi  and  maternal  sinuses,  by  means  of  which  the 
blood  of  the  foetus  is  enriched  and  purified  after  the  fashion  necessary 
for  the  proper  growth  and  development  of  those  parts  which  it  is  de- 
signed to  nourish. 

The  importance  of  the  placenta  is  at  once  apparent  if  we  remember 
that  during  the  greater  portion  of  intra-uterine  life  the  maternal  blood 
circulating  in  its  vessels  supplies  the  foetus  with  both  food  and  oxygen. 
It  thus  performs  the  functions  which  in  later  life  are  discharged  by  the 
alimentary  canal  and  lungs. 

The  whole  of  this  structure  is  not,  as  might  be  imagined,  thrown  off 
immediately  after  birth.  The  greater  part,  indeed,  comes  away  at  that 
time,  as  the  after-birth;  and  the  separation  of  this  portion  takes  place 
by  a  rending  or  crushing  through  of  that  part  at  which  its  cohesion  is 
least  strong,  namely,  where  it  is  most  burrowed  and  undermined  by  the 
cavernous  spaces  before  referred  to.  In  this  way  it  is  cast  off  with  the 
foetal  membrane  and  the  decidua  vera  and  reflexa,  together  with  a  part 
of  the  decidua  serotina.  The  remaining  portion  withers,  and  disappears 
by  being  gradually  either  absorbed,  or  thrown  off  in  the  uterine  dis- 
charges or  the  lochia,  which  occur  at  this  period. 

A  new  mucous  membrane  is  of  course  gradually  developed,  as  the  old 
one,  by  its  transformation  into  the  decidua,  ceases  to  perform  its  original 
functions. 

The  umbilical  cord,  which  in  the  latter  part  of  foetal  life  is  almost 
solely  composed  of  the  two  arteries  and  the  single  vein  which  respectively 
convey  foetal  blood  to  and  from  the  placenta,  contains  the  remnants  of 
other  structures  which  in  the  early  stages  of  the  development  of  the  em- 
bryo were,  as  already  related,  of  great  comparative  importance.  Thus, 
in  early  foetal  life,  it  is  composed  of  the  following  parts: — (1.)  Exter- 
nally, a  layer  of  the  amnion,  reflected  over  it  from  the  umbilicus.  (2.) 
The  umbilical  vesicle  with  its  duct  and  appertaining  omphalo-mesenteric 
blood-vessels.  (3.)  The  remains  of  the  allantois,  and  continuous  with  it 
the  urachus.  (4.)  The  umbilical  vessels,  which,  as  just  remarked,  ulti- 
mately form  the  greater  part  of  the  cord. 

The  Development  of  the  Oegans. 

It  remains  now  to  consider  in  succession  the  development  of  the 
several  organs  and  systems  of  organs  in  the  further  progress  of  the  em- 
bryo. The  accompanying  figure  (Fig.  466)  shows  the  chief  organs  of  the 
body  in  a  moderately  early  stage  of  development. 

The  Vertebral  Column  and  Cranium  — The  primitive  part  of 
the  vertebral  column  in  all  the  Vertebrata  is  the  chorda  dorsalis  (noto- 
chord),  which  consists  entirely  of  soft  cellular  cartilage.  This  cord 
tapers  to  a  point  at  the  cranial  and  caudal  extremities  of  the  animal.   In 


DEVELOPMENT. 


679 


the  progress  of  its  development,  it  is  found  to  become  inclosed  in  a 
membranous  sheath,  which  at  length  acquires  a  fibrous  structure,  com- 
posed of  transverse  annular  fibres.  The  chorda  dorsal's  is  to  be  regarded 
as  the  azygos  axis  of  the  spinal  column,  and,  in  particular,  of  the  future 
bodies  of  the  vertebrae,  although  it  never  itself  passes  into  the  state  of 
hyaline  cartilage  or  bone,  but  remains  inclosed  as  in  a  case  within  the 
persistent  parts  of  the  vertebral  column  which  are  developed  around  it. 
It  is  permanent,  however,  only  in  a  few  animals;  in  the  majority  only 
traces  of  it  persist  in  the  adult  animal. 

In  many  Fish  no  true  vertebrae  are  developed,  and  there  is  every  gra- 
dation from  the  amphi ox  us,  in  which  the  notochord  persists  through  life 
and  there  are  no  vertebrae,  through  the  lampreys  in  which  there  are  a 
few  scattered  cartilaginous  vertebrae,  and  the  sharks,  in  which  many  of 


G.Fh 


-vie 


Ce^-V  jvt  Tr     IF 


Fig.  466.— Embryo  chick  (4th  day\  viewed  as  a  transparent  object,  lying  on  its  left  side  (mag- 


second,  third,  and  fourth  visceral  folds;  V,  fifth  nerve,  sending  one  branch  ( ophthalmic )  to  the  eye, 
and  another  to  the  first  visceral  arch;  VII,  seventh  nerve,  passing  to  the  second  visceral  arch: 
G.Ph,  glosso-pharyngeal  nerve,  passing  to  the  third  visceral  arch;  P  </,  pneumogastric  nerve,  pass- 
ing  towards  the  fourth  visceral  arch;  iv.  investing  mass;  ch.  notochord;  its  front  end  cannot  be 
seen  in  the  living  embryo,  and  it  does  not  end  as  shown  in  the  figure,  but  takes  a  sudden  bend  down- 
wards, and  then  terminates  in  a  point;  Ht,  heart  seen  through  the  walls  of  the  chest ;  MP.  muscle 
plates;  W,  wing,  showing  commencing  differentiation  of  segments,  corresponding  to  arm.  forearm, 
and  hand;  HL,  hind-limb,  as  yet  a  shapeless  bud,  showing  no  differentiation.  Beneath  it  is  seen 
the  curved  tail.    (Foster  and  Balfour,  i 


the  vertebrae  are  partly  ossified,  to  the  bony  fishes,  such  as  the  cod  and 
herring,  in  which  the  vertebral  column  consists  of  a  number  of  distinct 
ossified  vertebrae,  with  remnants  of  the  notochord  between  them.  In 
Amphibia,  Reptiles,  Birds,  and  Mammals,  there  are  distinct  vertebrae, 
which  are  formed  as  follows: — 

The   mesoblastic  somites,  which  have    been  already  mentioned   (p. 
666),  send  processes  downwards  and  inwards  to  surround  the  notochord, 


680  HANDBOOK    OF    PHYSIOLOGY. 

and  also  upwards  between  the  medullary  canal  and  the  epiblast  covering 
it.  In  the  former  situation,  the  cartilaginous  bodies  of  the  vertebrge 
make  their  appearance,  in  the  latter  their  arches,  which  inclose  the  neu- 
ral canal. 

The  vertebra?  do  not  exactly  correspond  in  their  position  with  the 
proto vertebras:  but  each  permanent  vertebra  is  developed  from  the  con- 
tiguous halves  of  two  protovertebras.  The  original  segmentation  of  the 
protovertebras  disappears,  and  a  fresh  subdivision  occurs  in  such  a  way 
that  a  permanent  invertebral  disc  is  developed  opposite  the  centre  of 
each  protovertebra.  Meanwhile  the  protovertebras  split  into  a  dorsal 
and  ventral  portion.  The  former  is  termed  the  musculo-cutaneous  plate, 
and  from  it  are  developed  all  the  muscles  of  the  back  together  with  the 
cutis  of  the  dorsal  region  (the  epidermis  being  derived  from  the  epiblast). 
The  ventral  portions  of  the  protovertebra?,  as  we  have  already  seen,  give 
rise  to  the  vertebras  and  heads  of  the  ribs. 

The  chorda  is  now  inclosed  in  a  case,  formed  by  the  bodies  of  the 
vertebras,  but  it  gradually  wastes  and  disappears.  Before  the  disappear- 
ance of  the  chorda,  the  ossification  of  the  bodies  and  arches  of  the  verte- 
brae begins  at  distinct  points. 

The  ossification  of  the  body  of  a  vertebra  is  first  observed  at  the  point 
where  the  two  primitive  elements  of  the  vertebras  have  united  inferiorly. 
Those  vertebras  which  do  not  bear  ribs,  such  as  the  cervical  vertebras, 
have  generally  an  additional  centre  of  ossification  in  the  transverse  pro- 
cess, which  is  to  be  regarded  as  an  abortive  rudiment  of  a  rib.  In  the 
foetal  bird,  these  additional  ossified  portions  exist  in  all  the  cervical  ver- 
tebras, and  gradually  become  so  much  developed  in  the  lower  part  of  the 
cervical  region  as  to  form  the  upper  false  ribs  of  this  class  of  animals. 
The  same  parts  exist  in  mammalia  and  man;  those  of  the  last  cervical 
vertebras  are  the  most  developed,  and  in  children  may,  for  a  considerable 
period,  be  distinguished  as  a  separate  part  on  each  side  like  the  root  or 
head  of  a  rib. 

The  true  cranium  is  a  prolongation  of  the  vertebral  column,  and  is 
developed  at  a  much  earlier  period  than  the  facial  bones.  Originally  it 
is  formed  of  but  one  mass,  a  cerebral  capsule,  the  chorda  dorsalis  being 
continued  into  its  base,  and  ending  there  with  a  tapering  point.  At  an 
early  period  the  head  is  bent  downwards  and  forwards  round  the  end  of 
the  chorda  dorsalis  in  such  a  way  that  the  middle  cerebral  vesicle,  and 
not  the  anterior,  comes  to  occupy  the  highest  position  in  the  head. 

Pituitary  Body. — In  connection  with  this  must  be  mentioned  the 
development  of  the  pituitary  body.  It  is  formed  by  the  meeting  of  two 
out-growths,  one  from  the  foetal  brain,  which  grows  downwards,  and  the 
other  from  the  epiblast  of  the  buccal  cavity,  which  grows  up  towards  it. 
The  surrounding  mesoblast  also  takes  part  in  its  formation.  The  con- 
nection of  the  first  process  with  the  brain  becomes  narrowed,  and  per- 


DEVELOPMENT.  6  s  1 

sists  as  the  infundibulum,  while  that  of  the  other  piocess  with  the  buc- 
cal cavity  disappears  completely  at  a  spot  corresponding  with  the  future 
position  of  the  body  of  the  sphenoid. 

Cranium. 

The  first  appearance  of  a  solid  support  at  the  base  of  the  cranium  ob- 
served by  Muller  in  fish,  consists  of  two  elongated  bands  of  cartilage 
(trabecular  cranii),  one  on  the  right  and  the  other  on  the  left  side,  which 
are  connected  with  the  cartilaginous  capsule  of  the  auditory  apparatus, 
and  which  diverge  to  inclose  the  pituitary  body,  uniting  in  front  to 
form  the  septum  nasi  beneath  the  anterior  end  of  the  cerebral  capsule. 
Hence,  in  the  cranium,  as  in  the  spinal  column,  there  are  at  first  de- 
veloped at  the  sides  of  the  chorda  dorsalis  two  symmetrical  elements, 
which  subsequently  coalesce,  and  may  wholly  inclose  the  chorda. 

The  brain-case  consists  of  three  segments:  occipital,  parietal,  and 
frontal,  corresponding  in  their  relative  position  to  the  three  primitive 
cerebral  vesicles;  it  may  also  be  noted  that  in  front  of  each  segment  is 
developed  a  sense-organ  (auditory,  ocular,  and  olfactory,  from  behind 
forwards).  The  basis  cranii  consists  at  an  early  period  of  an  unseg- 
mented  cartilaginous  rod,  developed  round  the  notochord,  and  continued 
forward  beyond  its  termination  into  the  trabecuke  cranii,  which  bound 
the  pituitary  fossa  on  either  side. 

In  this  cartilaginous  rod  three  centres  of  ossification  appear:  basi- 
occipital,  basi-sphenoid,  and  pre-sphenoid,  one  corresponding  to  each 
segment. 

The  bones  forming  the  vault  of  the  skull,  viz.,  the  frontal,  parietal, 
squamous  portion  of  temporal  and  the  squamo-occipital,  are  ossified  in 
membrane. 

The  Visceral  Clefts  and  Arches. 

As  the  embryo  enlarges,  the  heart,  which  at  first  occupied  a  position 
close  to  the  cranial  flexure,  is  carried  further  and  further  backwards 
until  a  considerable  intervening  part  exists  between  it  and  the  head,  in 
which  the  mesoblast  is  undivided.  This  becomes  the  neck.  On  a  sec- 
tion it  is  seen  that  in  it  the  whole  three  layers  are  represented  in  order, 
and  that  there  is  no  interval  between  them.  In  the  neck  thus  formed 
soon  appear  the  visceral  or  branchial  clefts  on  either  side,  in  series, 
across  the  axis  of  the  gut  not  quite  at  right  angles.  They  are  four  in 
number,  the  most  anterior  being  first  found.  At  their  edges  the  hypo- 
blast and  the  epiblast  are  continuous.  The  anterior  border  of  each  cleft 
forms  a  fold  or  lip,  the  branchial  or  visceral  fold.  The  posterior  bor- 
der of  the  last  cleft  is  also  formed  into  a  fold,  so  that  there  are  four 
clefts  and  five  folds,  hut  the  three  most  anterior  are  far  more  prominent 


682  HANDBOOK    OF    PHYSIOLOGY. 

than  the  others,  and  of  these  the  second  is  the  most  conspicuous.  The 
first  fold  nearly  meets  its  fellow  in  the  middle  line,  the  second  less 
nearly,  and  the  others  in  order  still  less  so.  Thus  in  the  neck  there  is 
a  triangular  interval,  into  which  by  the  splitting  of  the  mesoblast  at 
that  part  the  pleuro-peritoneal  cavity  extends.  The  branchial  clefts 
and  arches  are  not  all  permanent.  The  first  arch  gives  off  a  branch 
from  its  front  edge,  which  passes  forwards  to  meet  its  fellow,  but  these 
offshoots  do  not  quite  meet,  being  separated  by  a  process  which  grows 
downwards  from  the  head.  Between  the  branches  and  the  main  first 
fold  is  the  cavity  of  the  mouth.  The  branches  represent  the  superior 
maxilla,  and  the  main  folds  the  mandible  or  lower  jaw.  The  central 
process,  which  grows  down,  is  the  fronto-nasal  process. 

In  this  way,  the  so-called  visceral  arches  and  clefts  are  formed,  four 
on  each  side  (Fig.  467,  a). 

From  or  in  connection  with  these  arches  the  following  parts  are  de- 
veloped:— 


Fig.  467. — a.  Magnified  view  from  before  of  the  head  and  neck  of  a  human  embryo  of  about 
three  weeks  (from  Eeker).—1,  anterior  cerebral  vesicle  or  cerebrum;  2,  middle  ditto;  3,  middle  or 
fronto-nasal  process;  4,  superior  maxillary  process;  5,  eye;  6,  inferior  maxillary  process,  or  first 
visceral  arch,  and  below  it  is  the  first  cleft;  7.  8,  9,  second,  third,  and  fourth  arches  and  clefts,  b. 
Anterior  view  of  the  head  of  a  human  foetus  of  about  the  fifth  week  (from  Ecker,  as  before  fig.  rv.). 
1,  2,  3,  5,  the  same  parts  as  in  a;  4,  the  external  nasal  or  lateral  frontal  process;  6,  the  superior 
maxillary  process;  7,  the  lower  jaw;  x,  the  tongue;  8,  first  branchial  cleft  becoming  the  meatus 
auditorius  externus. 

The  first  arch  (mandibular)  contains  a  cartilaginous  rod  (Meckel's 
cartilage),  around  the  distal  edge  of  which  the  lower  jaw  is  developed, 
while  the  malleus  is  ossified  from  the  proximal  end. 

When  the  maxillary  processes  on  the  two  sides  fail  partially  or  com- 
pletely to  unite  in  the  middle  line,  the  well-known  condition  termed 
deft  palate  results.  When  the  integument  of  the  face  presents  a  similar 
deficiency,  we  have  the  deformity  known  as  hare-lip.  Though  these 
two  deformities  frequently  co-exist,  they  are  by  no  means  always  neces- 
sarily associated. 

The  upper  part  of  the  face  in  the  middle  line  is  developed  from  the 
so-called  frontal-nasal  process  (a,  3,  Fig.  467).  From  the  second  arch 
are  developed  the  incus,  stapes,  and  stapedius  muscle,  the  styloid  pro- 
cess of  the  temporal  bone,  the  stylo-hyoid  ligament,  and  the  smaller 
cornu  of  the  hyoid  bone.     From  the  third  visceral  arch,  the  greater 


DEVELOPMENT. 


683 


cor uu  and  body  of  the  hyoid  bone.  In  man  and  other  mammalia  the 
fourth  visceral  arch  is  indistinct.  It  occupies  the  position  where  the 
neck  is  afterwards  developed. 

A  distinct  connection  is  traceable  between  these  visceral  arches  and 
certain  cranial  nerves:  the  trigeminal,  the  facial,  the  glosso-pharyngeal, 
and  the  pneumogastric.  The  ophthalmic  division  of  the  trigeminal  sup- 
plies the  trabecular  arch;  the  superior  and  inferior  maxillary  divisions 
supply  the  maxillary  and  mandibular  arches  respectively. 

The  facial  nerve  distributes  one  branch  (chorda  tympani)  to  the  first 
visceral  arch,  and  others  to  the  second  visceral  arch.  Thus  it  divides, 
inclosing  the  first  visceral  cleft. 

Similarly,  the  glosso-pharyngeal  divides  to  inclose  the  second  visceral 


/    /    /  /„„ 


Fig.  468.— Embryo  chick  (4th  day"),  viewed  as  a  transparent  object,  lying  on  its  left  side  (mag- 
nified"). C  H,  cerebral  hemispheres:  F B,  fore-brain  or  vesicle  of  third  ventricle,  with  Pn.  pineal 
gland  projecting  from  its  summit:  MB,  mid-brain;  C  b,  cerebellum;  TV.  V,  fourth  ventricle;  L, 
lens:  chs.  choroidal  slit:  Cen.  V,  auditory  vesicle;  .s  m,  superior  maxillary  process;  IF.  -2F,  etc..  first. 
second,  third,  and  fourth  visceral  folds;  V,  fifth  nerve,  sending  one  branch  (ophthalmic  >  to  the  eye. 
and  another  to  the  first  visceral  arch;  VII,  seventh  nerve,  passing  to  the  second  visceral  arch; 
G.Ph,  glosso-pharyngeal  nerve,  passing  to  the  third  visceral  arch;  P  (/,  pneumogastric  nerve,  pass- 
ing towards  the  fourth  visceral  arch;  it),  investing  mass;  ch,  notochord;  its  front  end  cannot  be 
seen  iu  the  living  embryo,  and  it  does  not  end  as  shown  in  the  figure,  but  takes  a  sudden  bend  down- 
wards, and  theu  terminates  in  a  point;  Ht.  heart  seen  through  the  walls  of  the  chest;  MP,  muscle 
plates:  W,  wing,  showing  commencing  differentiation  of  segments,  corresponding  to  arm,  forearm, 
and  hand;  S  S,  somatic  stalk ;  Al,  allantois;  HL,  hind-limb,  as  yet  a  shapeless  bud,  showing  no 
differentiation.    Beneath  it  is  seen  the  curved  tail.    (.Foster  and  Balfour.) 

cleft,  its  lingual  branch  being  distributed  to  the  second,  and  its  pharyn- 
geal branch  to  the  third  arch. 

The  vagus,  too,  sends  a  branch  (pharyngeal)  along  the  third  arch, 
and  in  fishes  it  gives  off  paired  branches,  which  divide  to  inclose  succes- 
sive branchial  clefts. 

The  Extremities. 
The  extremities  are  developed  in  a  uniform  manner  in  all  vertebrate 
animals.     They  appear  in  the  form  of  leaf-like  elevations  from  the  pari- 
ctes  of  the  trunk  (see  Fig.  4G8),  at  points  where  more  or  less  of  an  arch 


6S4 


HAKDBOOK    OF    PHYSIOLOGY. 


will  be  produced  for  them  within.  The  primitive  form  of  the  extremity 
is  nearly  the  same  in  all  Vertebrata,  whether  it  be  destined  for  swim- 
ming, crawling,  walking,  or  flying.  In  the  human  foetus  the  fingers  are 
at  first  united,  as  if  webbed  for  swimming;  but  this  is  to  be  regarded 
not  so  much  as  an  approximation  to  the  form  of  aquatic  animals,  as  the 
primitive  form  of  the  hand,  the  individual  parts  of  which  subsequently 
become  more  completely  isolated. 

The  fore-limb  always  appears  before  the  hind-limb,  and  for  some  time 
continues  in  a  more  advanced  state  of  development.  In  both  limbs  alike, 
the  distal  segment  (hand  or  foot)  is  separated  by  a  slight  notch  from  the 
proximal  part  of  the  limb,  and  this  part  is  subsequently  divided  again 
by  a  second  notch  (knee  or  elbow-joint). 

The  Vascular  System. — At  an  early  stage  in  the  development  of 
the  embryo  chick,  the  so-called  "area  vasculosa"  begins  to  make  its 
appearance.     A  number  of  branched  cells  in  the  mesoblast  send  out  pro- 


Fig.  469. — A  human  embryo  of  the  fourth  week,  3X  lines  in  length. — 1,  the  chorion;  3,  part  of 
the  amnion;  4,  umbilical  vesicle  with  its  long  pedicle  passing  into  the  abdomen;  7,  the  heart;  8,  the 
liver;  9,  the  visceral  arch  destined  to  form  the  lower  jaw,  beneath  which  are  two  other  visceral 
arches  separated  by  the  branchial  clefts;  10,  rudiment  of  the  upper  extremity;  11,  that  of  the  lower 
extremity;  12,  the  umbilical  cord;  15,  the  eye;  16,  the  ear;  17,  cerebral  hemispheres;  18,  optic  lobes, 
corpora  quadrigemina.    (Muller.) 


cesses  which  unite  so  as  to  form  a  network  of  protoplasm  with  nuclei  at 
the  nodal  points.  A  large  number  of  the  nuclei  acquire  a  red  color; 
these  form  the  red  blood-cells.  The  protoplasmic  processes  become 
hollowed  out  in  the  centre  so  as  to  form  a  closed  system  of  branching 
canals,  in  the  walls  of  which  the  rest  of  the  nuclei  remain  imbedded.  In 
the  blood-vessels  thus  formed,  the  circulation  of  the  embryonic  blood 
commences. 

According  to  Klein's  researches,  the  first  blood-vessels  in  the  chick 
are  developed  from  embryonic  cells  of  the  mesoblast,  which  swell  up  and 
become  vacuolated,  while  their  nuclei  undergo  segmentation.  These 
cells  send  out  protoplasmic  processes,  which  unite  with  corresponding 
ones  from  other  cells,  and  become  hollowed,  give  rise  to  the  capillary 


DEVELOPMENT, 


685 


wall  composed  of  endothelial  cells;  the  blood-corpuscles  being  budded 
off  from  the  endothelial  wall  by  a  process  of  gemmation. 

Heart. — About  the  same  early  period  the  heart  makes  its  appearance 
as  a  solid  mass  of  cells  of  the  splanchno-pleure  in  the  manner  before  in- 
dicated. 

At  this  period  the  anterior  part  of  the  alimentary  tube  ends  bliudlv 
beneath  the  notochcord.  It  is  beneath  the  posterior  end  of  this  fore-gut 
that  the  heart  begins  to  be  developed.     The  heart  when  first  formed  is 


Fig.  470.— Capillary  blood-vessels  of  the  tail  of  a  young  larval  frog,  a,  capillaries  permeable  to 
blood;  b,  fat  granules  attached  to  the  walls  of  the  vessels,  and  concealing  the  nuclei;  r,  hollow  pro- 
longation of  a  capillary,  ending  in  a  point;  rf,  a  branching  cell  with  nucleus  and  fat-granules;  it 
communicates  by  three  branches  with  prolongation  of  capillaries  already  formed;  e,  e,  blood  cor- 
puscles still  containing  granules  of  fat.    x  350  times.    <  Kolliker.) 

made  up  of  two  not  quite  complete  tubes  which  coalesce  to  form  one, 
and  so  when  the  cavity  is  hollowed  out  in  the  mass  of  cells,  the  central 
cells  float  freely  in  the  fluid,  which  soon  begins  to  circulate  by  means  of 
the  rhythmic  pulsations  of  the  embryonic  heart. 

These  pulsations  take  place  even  before  the  appearance  of  a  cavity, 
and  immediately  after  the  first  "'  laving  down"  of  the  cells  from  which 
the  heart  is  formed,  and  long  before  muscular  fibres  or  ganglia  have 


6S6 


HANDBOOK    OF    PHYSIOLOGY. 


"been  formed  in  the  cardiac  walls.  At  first  they  seldom  exceed  from  fif- 
teen to  eighteen  in  the  minute.  The  fluid  within  the  cavity  of  the  heart 
shortly  assumes  the  characters  of  blood.  At  the  same  time  the  cavity 
itself  forms  a  communication  with  the  great  vessels  in  contact  with  it, 
and  the  cells  of  which  its  walls  are  composed  are  transformed  into 
fibrous  and  muscular  tissues,  and  into  epithelium.  In  the  developing 
chick  it  can  be  observed  with  the  naked  eye  as  a  minute  red  pulsating 
point  before  the  end  of  the  second  day  of  incubation. 

Blood-vessels. — Blood-vessels  appear  to  be  developed  in  two  ways,  ac- 
cording to  the  size  of  the  vessels.  In  the  formation  of  large  blood-vessels, 
masses  of  embryonic  cells  similar  to  those  from  which  the  heart  and 
other  structures  of  the  embryo  are  developed,  arrange  themselves  in  the 
position,  form,  and  thickness  of  the  developing  vessel.  Shortly  after- 
wards the  cells  in  the  interior  of  a  column  of  this  kind  seem  to  be  de- 


Fig.  461. 


Fig.  462. 


Fig.  471.— Development  of  capillaries  in  the  regenerating  tail  of  a  tadpole,  a,  b,  c,  d,  sprouts 
and  cords  of  protoplasm.    (Arnold.) 

Fig.  472.— The  same  region  after  the  lapse  of  24  hours.  The  "  sprouts  and  cords  of  protoplasm  " 
have  become  channelled  out  into  capillaries.    (Arnold.) 

veloped  into  blood-corpuscles,  while  the  external  layer  of  cells  is  con- 
verted into  the  walls  of  the  vessel. 

In  the  development  of  capillaries  another  plan  is  pursued.  This  has 
been  well  illustrated  by  Kolliker,  as  observed  in  the  tails  of  tadpoles. 
The  first  lateral  vessels  of  the  tail  have  the  form  of  simple  arches,  pass- 
ing between  the  main  artery  and  vein,  and  are  produced  by  the  junction 
of  prolongations,  sent  from  both  the  artery  and  vein,  with  certain  elon- 
gated or  star-shaped  cells,  in  the  substance  of  the  tail.  When  these 
arches  are  formed  and  are  permeable  to  blood,  new  prolongations  pass 
from  them,  join  other  radiated  cells,  and  thus  form  secondary  arches. 
In  this  manner,  the  capillary  network  extends  in  proportion  as  the  tail 
increases  in  length  and  breadth,  and  it,  at  the  same  time,  becomes  more 
dense  by  the  formation,  according  to  the  same  plan,  of  fresh  vessels 


DEVELOPMENT. 


68' 


within  its  meshes.  The  prolongations  by  which  the  vessels  communi- 
cate with  the  star-shaped  cells,  consist  at  first  of  narrow  pointed 
projections  from  the  side  of  the  vessels,  which  gradually  elongate  until 
they  come  in  contact  with  the  radiated  processes  of  the  cells.  The 
thickness  of  such  a  prolongation  often  does  not  exceed  that  of  a  fibril  of 
fibrous  tissue,  and  at  first  it  is  perfectly  solid;  but,  by  degrees,  especially 
after  its  junction  with  a  cell,  or  with  another  prolongation,  or  with  a 
vessel  already  permeable  to  blood,  it  enlarges,  and  a  cavity  then  forms  in 
its  interior  (see  Figs.  470,  472).  This  tissue  is  well  calculated  to  illus- 
trate the  various  steps  in  the  development  of  blood-vessels  from  elon- 
gating and  branching  cells. 

In  many  cases  a  whole  network  of  capillaries  is  developed  from  a  net- 
work of  branched,  embryonic  connective-tissue  corpuscles  by  the  joining 
of  their  processes,  the  multiplication  of  their  nuclei,  and  the  vacuolation 
of  the  cell-substance.     The  vacuoles  gradually  coalesce  till  all  the  parti- 


Fig.  473.— Capillaries  from  the  vitreous  humor  of  a  foetal  calf.  Two  vessels  are  seen  connected 
by  a  ''  cord  "  of  protoplasm,  and  clothed  with  an  adventitia,  containing  numerous  nuclei;  a,  inser- 
tion of  this  "  cord  "  into  the  primary  walls  of  the  vessels.    (Frey.) 


tions  are  broken  down,  and  the  originally  solid  protoplasmic  cell-substance 
is,  so  to  speak,  tunnelled  out  into  a  number  of  tubes. 

Capillaries  may  also  be  developed  from  cells  which  are  originally 
spheroidal,  vacuoles  form  in  the  interior  of  the  cells  gradually  becoming 
united  by  fine  protoplasmic  processes:  by  the  extension  of  the  vacuoles 
into  them,  capillary  tubes  are  gradually  formed. 

Morphology  Heart. — When  it  first  appears,  the  heart  is  approximately 
tubular  in  form,  being  at  first  a  double  tube,  then  a  single  one.  It 
receives  at  its  two  posterior  angles  the  two  omphalo-mesenteric  or  vitel- 
line veins,  and  gives  off  anteriorly  the  primitive  aorta  (Fig.  474).  The 
junction  of  the  two  veins  which  pass  into  the  auricle  becomes  removed 
farther  and  farther  away  from  the  heart,  and  the  vessel  thus  formed  is 
called  sinus  venosusnear  to  the  auricle,  and  ductus  venosus  farther  away, 
or  if  it  be  called  by  one  name,  that  of  meatus  venosus  may  be  used. 


688 


HANDBOOK    OF    PHYSIOLOQY. 


It  soon,  however,  becomes  curved  somewhat  in  the  shape  of  a  horse- 
shoe, with  the  convexity  towards  the  right,  the  venous  end  being  at  the 
same  time  drawn  up  towards  the  head,  so  that  it  finally  lies  behind  and 
somewhat  to  the  right  of  the  arterial.  It  also  becomes  partly  divided  by 
constrictions  into  three  cavities. 

Of  these  three  cavities  which  are  developed  in  all  Vertebrata,  that  at 
the  venous  end  is  the  simple  auricle,  with  the  sinus  venosus,  that  at  the 
arterial  end  the  bulbus  arteriosus,  and  the  middle  one  is  the  simple  ven- 
tricle. 


Fig.  474. — Foetal  heart  in  successive  stages  of  development.    1,  venous  extremity;  2,  arterial 
extremity;  3,  8,  pulmonary  branches;  4,ductus  arteriosus.     (Dalton.) 

These  three  parte  of  the  heart  contract  in  succession.  The  auricle 
and  the  bulbus  arteriosus  at  this  period  lie  at  the  extremities  of  the  horse- 
shoe. The  bulging  out  of  the  middle  portion  inferiorly  gives  the  first 
indication  of  the  future  form  of  the  ventricle  (Fig.  475).     The  great 


Fig.  475.— Heart  of  the  chick  at  the  45th,  65th,  and  85th  hours  of  incubation.    1 ,  the  venous 
trunks;  2,  the  auricle;  3,  the  ventricle;  4,  the  bulbus  arteriosus.    (Allen  Thomson.) 

curvature  of  the  horse-shoe  by  the  same  means  becomes  much  more  de- 
veloped than  the  smaller  curvature  between  the  auricle  and  bulbus;  and 
the  two  extremities,  the  auricle  and  bulb,  approach  each  other  superiorly, 
so  as  to  produce  a  greater  resemblance  to  the  later  form  of  the  heart, 
whilst  the  ventricle  becomes  more  and  more  developed  inferiorly.  The 
heart  of  Fishes  retains  these  four  cavities,  no  further  division  by  inter- 
nal septa  into  right  and  left  chambers  taking  place.  In  Amphibia, 
also,  the  heart  throughout  life  consists  of  the  three  muscular  divisions 
which  are  so  early  formed  in  the  embryo  and  the  sinus  venosus;  but  the 


DEVELOPMENT.  681) 

auricle  is  divided  internally  by  a  septum  into  a  pulmonary  and  systemic 
auricle.  In  reptiles,  not  merely  the  auricle  is  thus  divided  into  two 
cavities,  but  a  similar  septum  but  incomplete  is  more  or  less  developed 
in  the  ventricle.  In  Birds  and  Mammals,  both  auricle  and  ventricle 
undergo  complete  division  by  septa;  whilst  in  these  animals  as  well  as  in 
reptiles,  the  bulbus  aortae  is  not  permanent,  but  becomes  lost  in  the  ven- 
tricles. The  septum  dividing  the  ventricle  commences  at  the  apex  and 
extends  upwards.  The  subdivision  of  the  auricles  is  very  early  fore- 
shadowed by  the  outgrowth  of  the  two  auricular  appendages,  which 
occurs  before  any  septum  is  formed  externally.  The  septum  of  the  auri- 
cles is  developed  from  a  semilunar  fold,  which  extends  from  above  down- 
wards. In  man,  the  septum  between  the  ventricles,  according  to  Meckel, 
begins  to  be  formed  about  the  fourth  week,  and  at  the  end  of  eight 
weeks  is  complete.  The  septum  of  the  auricles,  in  man  and  all  animals 
which  possess  it,  remains  imperfect  throughout  foetal  life.  When  the 
partition  of  the  auricles  is  first  commencing,  the  two  venae  cavae  have 
different  relations  to  the  two  cavities.  The  superior  cava  enters,  as  in 
the  adult,  into  the  right  auricle;  but  the  inferior  cava  is  so  placed  that 
it  appears  to  enter  the  left  auricle,  and  the  posterior  part  of  the  septum 
of  the  auricles  is  formed  by  the  Eustachian  valve,  which  extends  from 
the  point  of  entrance  of  the  inferior  cava.  Subsequently,  however,  the 
septum,  growing  from  the  anterior  wall  close  to  the  upper  end  of  the 
ventricular  septum,  becomes  directed  more  and  more  to  the  left  of  the 
vena  cava  inferior.  During  the  entire  period  of  foetal  life,  there  remains 
an  opening  in  the  septum,  which  the  valve  of  the  foramen  ovale,  devel- 
oped in  the  third  month,  imperfectly  closes. 

The  bulbus  arteriosus,  which  is  originally  a  single  tube,  becomes 
gradually  divided  into  two  by  the  growth  of  an  internal  septum,  which 
springs  from  the  posterior  wall,  and  extends  forwards  towards  the  front 
wall  and  downwards  towards  the  ventricles.  This  partition  takes  a  some- 
what spiral  direction,  so  that  the  two  tubes  (aorta  and  pulmonary  artery) 
which  result  from  its  completion,  do  not  run  side  by  side,  but  are  twisted, 
round  each  other. 

As  the  septum  grows  down  towards  the  ventricles,  it  meets  and  coa- 
lesces with  the  upwardly  growing  ventricular  septum,  and  thus  from  the 
right  and  left  ventricles,  which  are  now  completely  separate,  arise  respec- 
tively the  pulmonary  artery  and  aorta,  which  are  also  quite  distinct.  The 
auriculo-ventricular  and  semilunar  valves  are  formed  by  the  growth  of 
folds  of  the  endocardium. 

At  its  first  appearance,  as  we  have  seen,  the  heart  is  placed  just  be- 
neath the  head  of  the  foetus,  and  is  very  large  relatively  to  the  whole 
body;  but  with  the  growth  of  the  neck  it  becomes  further  and  further 
removed  from  the  head,  and  is  lodged  in  the  cavity  of  the  thorax. 

Up  to  a  certain  period  the  auricular  is  larger  than  the  ventricular 
44 


690 


HANDBOOK    OF    PHYSIOLOGY. 


division  of  the  heart;  but  this  relation  is  gradually  reversed  as  develop- 
ment proceeds.  Moreover,  all  through  foetal  life,  the  walls  of  the  right 
ventricle  are  of  very  much  the  same  thickness  as  those  of  the  left,  which 
may  probably  be  explained  by  the  fact  that  in  the  foetus  the  right  ventri- 
cle has  to  propel  the  blood  from  the  pulmouary  artery  into  the  aorta, 
and  thence  into  the  placenta,  while  in  the  adult  it  only  drives  the  blood 
through  the  lungs. 

Arteries. — The  primitive  aorta  arises  from  the  bulbus  arteriosus  and 
divides  into  two  branches  which  arch  backwards,  one  on  each  side  of  the 
foregut  and  unite  again  behind  it,  and  in  front  of  the  notochord  into  a 
single  vessel. 

This  gives  off  the  two  omphalo-mesenteric  arteries,  which  distribute 
branches  all  over  the  yolk-sac;  this  area  vasculosa  in  the  chick  attaining 


Fig.  476.— Diagram  of  the  aortic  arches  in  the  mammal,  showing  transformations  which  give  rise 
to  the  permanent  arterial  vessels.  A,  primitive  arterial  stem  or  aortic  bulb,  now  divided  into  A,  the 
ascending  part  of  the  aortic  arch,  and  p,  the  pulmonary;  a,  a',  right  and  left  aortic  roots;  A',  de- 
scending aorta;  1,  2,  3,  4,  5,  the  five  primitive  aortic  or  branchial  arches;  I,  II,  III,  IV,  the  four 
branchial  clefts  which,  for  the  sake  of  clearness,  have  been  omitted  on  the  right  side.  The  per- 
manent systemic  vessels  are  deeply,  the  pulmonary  arteries  lightly,  shaded ;  the  parts  of  the 
primitive  arches  which  are  transitory  are  simply  outlined;  c,  placed  between  the  permanent  com- 
mon carotid  arteries;  ce,  external  carotic  arteries;  ci,  internal  carotid  arteries;  s,  right  subclavian, 
rising  from  the  right  aortic  root  beyond  the  fifth  arch;  v,  right  vertebral  from  the  same,  opposite 
the  fourth  arch;  v',  s',  left  vertebral  and  subclavian  arteries  rising  together  from  the  left,  or  per- 
manent aorticroot,  opposite  the  fourth  arch,  p,  pulmonary  arteries  rising  together  from  the  left 
fifth  arch;  d,  outer  or  back  part  of  left  fifth  arch  forming  ductus  arteriosus;  pn,pn',  right  and  left 
pneumogastric  nerves  descending  in  front  of  aortic  arch,  with  their  recurrent  branches  represented 
diagram matically  as  passing  behind  to  illustrate  the  relations  of  these  nerves  respectively  to  the 
right  subclavian  artery  (4;,  and  the  arch  of  the  aorta  and  ductus  arteriosus  (d).  (Allen  Thomson, 
after  Rathke.) 

a  large  development,  and  being  limited  all  round  by  a  vessel  known  as 
the  sinus  terminalis. 

The  blood  is  collected  by  the  venous  channels,  and  returned  through 
the  omphalo-mesenteric  veins  to  the  heart. 

Behind   this  pair  of  primitive  aortic  arches,  four  more  pairs  make 


DEVELOPMENT. 


691 


their  appearance  successively,  so  that  there  are  five  pairs  in  all,  each  one 
running  along  one  of  the  visceral  arches. 

These  five  are  never  all  to  be  seen  at  once  in  the  embryo  of  higher 
animals,  for  the  two  anterior  pairs  gradually  disappear  while  the  poste- 
rior ones  are  making  their  appearance,  so  that  at  length  only  three 
remain. 

In  Fishes,  however,  they  all  persist  throughout  life  as  the  branchial 
arteries  supplying  the  gills,  while  in  Amphibia  three  pairs  persist 
throughout  life. 

In  Keptiles,  Birds,  and  Mammals,  further  transformations  occur. 

In  Eeptiles  the  fourth  pair  remains  throughout  life  as  the  perma- 
nent right  and  left  aorta;  in  Birds  the  right  one  remains  as  the  perma- 
nent aorta,  curving  over  the  right  bronchus  instead  of  the  left  as  in 
Mammals. 


Mg.  47 


Fig.  478. 


Fig.  477.  —Diagram  of  young  embryo  and  its  vessels,  showing  course  of  circulation  in  the  um- 
bilical vesicle;  and  also  that  of  the  allantois  (near  the  caudal  extremity  >,  which  is  just  commencing. 
(Dalton.) 

Fig.  478.— Diagram  of  embryo  and  its  vessels  at  a  later  stage,  showing  the  second  circulation. 
The  pharynx,  oesophagus,  and  intestinal  canal  have  become  further  developed,  and  the  mesenteric 
arteries  have  enlarged,  while  the  umbilical  vesicle  and  its  vascular  branches  are  very  much,  re- 
duced in  size.    The  large  umbilical  arteries  are  seen  passing  out  in  the  placenta.    (Dalton.) 

In  Mammals  the  left  fourth  aortic  arch  develops  into  the  permanent 
aorta,  the  right  one  remaining  as  the  subclavian  artery  of  that  side. 
Thus  the  subclavian  artery  on  the  right  side  corresponds  to  the  aortic 
arch  on  the  left,  and  this  homology  is  further  confirmed  by  the  fact  that 
the  recurrent  laryngeal  nerve  hooks  under  the  subclavian  on  the  right 
side  and  the  aortic  arch  on  the  left. 

The  third  aortic  arch  remains  as  the  internal  carotid  artery,  while 
the  fifth  disappears  on  the  right  side,  but  on  the  left  forms  the  pulmo- 
nary artery.  The  distal  end  of  this  arch  originally  opens  into  the  de- 
scending aorta,  and  this  communication  (which  is  permanent  through- 
out life  in  many  reptiles  on  both  sides  of  the  body)  remains  throughout 


692 


HANDBOOK    OF    PHYSIOLOGY. 


foetal  life  under  the  name  of  ductus  arteriosus  :  the  branches  of  the  pul- 
monary artery,  to  the  right  and  left  lung,  are  very  small,  and  most  of 
the  blood  which  is  forced  into  the  pulmonary  artery  passes  through  the 
wide  ductus  arteriosus  into  the  descending  aorta.  All  these  points  will 
become  clear  on  reference  to  the  accompanying  diagram  (Fig.  476). 

As  the  umbilical  vesicle  dwindles  in  size,  the  portion  of  the  omphalo- 
mesenteric arteries  outside  the  body  gradually  disappears,  the  part  inside 
the  body  remaining  as  the  mesenteric  arteries. 

Meanwhile  with  the  growth  of  the  allantois  two  new  arteries  (umbil- 
ical) appear,  and  rapidly  increase  in  size  till  they  are  the  largest  branches 
of  the  aorta:  they  are  given  off  from  the  internal  iliac  arteries,  and  for  a 
long  time  are  considerably  larger  than  the  external  iliacs  which  supply 
the  comparatively  small  hind-limbs. 

Veins. — The  chief  veins  in  the  early  embryo  may  be  divided  into  two 
groups,  visceral  and  parietal:   the  former  includes  the  omphalo-mesen- 


*&4 


Z3 


J?* 


K 

<ntt  ^* 


Fig.  479.— Diagrams  illustrating  the  development  of  veins  about  the  liver.  B,  d  c,  ducts  of 
Cuvier,  right  and  left;  ca,  right  and  left  cardinal  veins;  o,  left  omphalo-mesenteric  vein;  o',  right 
omphalo-mesenteric  vein,  almost  shrivelled  up;  tt,  «',  umbilical  veins,  of  which  u',  the  right  one 
has  almost  disappeared.  Between  the  venae  cardinales  is  seen  the  outline  of  the  rudimentary  liver 
with  its  vense  hepaticae  advehentes,  and  revehentes.  D,  ductus  venosus;  l\  hepatic  veins;  ei,  vena 
cava  inferior;  P,  portal  vein;  P',  P',  venae  advehentes;  m,  mesenteric  veins.    (Kolliker.) 


teric  and  umbilical,  the  latter  the  jugular  and   cardinal  veins.     The 
former  may  be  first  considered. 

The  earliest  veins  to  appear  in  the  foetus  are  the  omphalo-mesenteric 
or  vitelline,  which  return  the  blood  from  the  yolk-sac  to  the  developing 
auricle.  As  soon  as  the  placenta  with  its  umbilical  veins  is  developed, 
these  unite  with  the  omphalo-mesenteric,  and  thus  the  blood  which 
reaches  the  auricle  comes  partly  from  the  yolk-sac  and  partly  from  the 
placenta.  The  right  omphalo-mesenteric  and  the  right  umbilical  vein 
soon  disappear,  and  the  united  left  omphalo-mesenteric  and  umbilical 
veins  pass  through  the  developing  liver  on  the  way  to  the  auricle.  Two 
sets  of  vessels  make  their  appearance  in  connection  with  the  liver  (vense 
hepaticae  advehentes,  and  revehentes),  both  opening  into  the  united 
omphalo-mesenteric  and  umbilical  veins,  in  such  a  way  that  a  portion  of 
the  venous  blood  traversing  the  latter  is  diverted  into  the  developing 


DEVELOPMENT.  693 

liver,  and,  having  passed  through  its  capillaries,  returns  to  the  umbili- 
cal vein  through  the  venae  hepaticae  revehentes  at  a  point  nearer  the 
heart  (see  Fig.  479).  The  portion  of  vein  between  the  afferent  and 
efferent  veins  of  the  liver  becomes  the  ductus  venosus.  The  venae  he- 
paticae advehentes  become  the  right  and  left  branches  of  the  portal  vein, 
the  venae  hepaticge  revehentes  become  the  hepatic  veins,  which  open  just 
at  the  junction  of  the  ductus  venosus  with  another  large  vein  (vena  cava 
inferior),  which  is  now  being  developed.  The  mesenteric  portion  of  the 
omphalo-mesenteric  vein  returning  blood  from  the  developing  intestines 
remains  as  the  mesenteric  vein,  which,  by  its  union  with  the  splenic 
vein,  forms  the  portal. 

Thus  the  foetal  liver  is  supplied  with  venous  blood  from  two  sources, 
through  the  umbilical  and  portal  vein  respectively.  At  birth  the  circu- 
lation through  the  umbilical  vein  of  course  completely  ceases  and  the 
vessel  begins  at  once  to  dwindle,  so  that  now  the  only  venous  supply  of 
the  liver  is  through  the  portal  vein.  The  earliest  appearance  of  the 
parietal  system  of  veins  is  the  formation  of  two  short  transverse  veins 
(ducts  of  Cuvier)  opening  into  the  auricle  on  either  side,  which  result 
from  the  union  of  an  anterior  cardinal,  afterwards  forming  a  jugular, 
vein,  collecting  blood  from  the  head  and  neck,  and  a  posterior  cardinal 
vein  which  returns  the  blood  from  the  Wolffian  bodies,  the  vertebral 
column,  and  the  parietes  of  the  trunk.  This  arrangement  persists 
throughout  life  in  Fishes,  but  in  Mammals  the  following  transforma- 
tions occur. 

As  the  kidneys  are  developing  a  new  vein  appears  (vena  cava  infe- 
rior), formed  by  the  junction  of  their  efferent  veins.  It  receives 
branches  from  the  leg  (iliac)  and  increases  rapidly  in  size  as  they  grow: 
further  up  it  receives  the  hepatic  veins,  which  by  now  have  lost  their 
original  opening  into  the  ductus  venosus.  The  heart  gradually  descends 
into  the  thorax,  causing  the  ducts  ef  Cuvier  to  become  oblique  instead 
of  transverse.  As  the  fore-limbs  develop,  the  subclavian  veins  are 
formed. 

A  transverse  communicating  trunk  now  unites  the  two  ducts  of 
Cuvier,  and  gradually  increases,  while  the  left  duct  of  Cuvier  becomes 
almost  entirely  obliterated  (all  its  blood  passing  by  the  communicating 
trunk  to  the  right  side)  (Fig.  480,  c.  D.).  The  right  duct  of  Cuvier  re- 
mains as  the  right  innominate  vein,  while  the  communicating  branch 
forms  the  left  innominate.  The  remnant  of  the  left  duct  of  Cuvier  gen- 
erally remains  as  a  fibrous  band,  running  obliquely  down  to  the  coronary 
vein,  which  is  really  the  proximal  part  of  the  left  duct  of  Cuvier.  In 
front  of  the  root  of  the  left  lung,  another  relic  maybe  found  in  the  form 
of  the  so-called  vestigial  fold  of  Marshall,  which  is  a  fold  of  pericardium 
running  in  the  same  direction. 


694: 


HANDBOOK    OF   PHYSIOLOGY. 


In  many  of  the  lower  mammals,  such  as  the  rat,  the  left  ductus  Cu- 
vieri  remains  as  a  left  superior  cava. 

Meanwhile,  a  transverse  branch  carries  across  most  of  the  blood  of 
the  left  posterior  cardinal  vein  into  the  right;  and  by  this  union  the 
great  azygos  vein  is  formed. 


Fig.  480.— Diagrams  illustrating  the  development  of  the  great  veins,  dc,  duets  of  Cuvier;  / 
jugular  veins;  h,  hepatic  veins;  c,  cardinal  veins;  s,  subclavian  vein;  ji,  internal  jugular  vein;  je 
external  jugular  vein;  <zz,  azygos  vein;  ci,  inferior  vena  cava;  r,  renal  veins;  il,  iliac  veins;  hij.  hy- 
pogastric veins.    (Gegenbauer.) 

The  upper  portions  of  the  left  posterior  cardinal  vein  remain  as  the 
left  superior  intercostal  and  vena  azygos  minor  (Fig.  480). 


Circulation  of  Blood  in  the  Fcetus. 

The  circulation  of  blood  in  the  foetus  differs  considerably  from  that 
of  the  adult.  It  will  be  well,  perhaps,  to  begin  its  description  by  trac- 
ing the  course  of  the  blood,  which,  after  being  carried  out  to  the  pla- 
centa by  the  two  umbilical  arteries,  has  returned,  cleansed  and  replen- 
ished, to  the  foetus  by  the  umbilical  vein. 

It  is  at  first  conveyed  to  the  under  surface  of  the  liver,  and  there  the 
stream  is  divided, — a  part  of  the  blood  passing  straight  on  to  the  inferior 
vena  cava,  through  a  venous  canal  called  the  ductus  venosus,  while  the 
remainder  passes  into  the  portal  vein,  and  reaches  the  inferior  vena 
cava  only  after  circulating  through  the  liver.  Whether,  however,  by  the 
direct  route  through  the  ductus  venosus  or  by  the  roundabout  way 
through  the  liver, — all  the  blood  which  is  returned  from  the  placenta 
by  the  umbilical  vein  reaches  the  inferior  vena  cava  at  last,  and  is  car- 
ried by  it  to  the  right  auricle  of  the  heart,  into  which  cavity  is  also 
pouring  the  blood  that  has  circulated  in  the  head  and  neck  and  arms, 


DEVELOPMENT. 


695 


and  has  been  brought  to  the  auricle  by  the  superior  vena  cava.  It 
might  be  naturally  expected  that  the  two  streams  of  blood  would  be 
mingled  in  the  right  auricle,  but  such  is  not  the  case,  or  only  to  a  slight 
extent.  The  blood  from  the  superior  vena  cava, — the  less  pure  fluid  of  the 
two— passes  almost  exclusively  into  the  right  ventricle,  through  the  au- 
riculo-ventricular  opening,  just  as  it  does  in  the  adult:  while  the  blood  of 


Fig.  481.— Diagram  of  the  Foetal  Circulation. 


the  inferior  vena  cava  is  directed  by  a  fold  of  the  lining  membrane  of 
the  heart,  called  the  Eustachian  valve,  through  the  foramen  ovale  into 
the  left  auricle,  whence  it  passes  into  the  left  ventricle,  and  out  of  this 
into  the  aorta,  and  thence  to  all  the  body,  but  chiefly  to  the  head  ami 
neck.  The  blood  of  the  superior  vena  cava,  which,  as  before  said. 
passes   into  the  right  ventricle,  is  sent    out    thence  in   small  amount 


696  HANDBOOK    OF    PHYSIOLOGY. 

through  the  pulmonary  artery  to  the  lungs,  and  thence  to  the  left  auri- 
cle, as  in  the  adult.  The  greater  part,  however,  hy  far,  does  not  go  to 
the  lungs,  but  instead,  passes  through  a  canal,  the  ductus  arteriosus, 
leading  from  the  pulmonary  artery  into  the  aorta  just  below  the  origin 
of  the  three  great  vessels  which  supply  the  upper  parts  of  the  body;  and 
there  meeting  that  part  of  the  blood  of  the  inferior  vena  cava  which 
has  not  gone  into  these  large  vessels,  it  is  distributed  with  it  to  the 
trunk  and  lower  parts — a  portion  passing  out  by  way  of  the  two  umbili- 
cal arteries  to  the  placenta.  From  the  placenta  it  is  returned  by  the 
umbilical  vein  to  the  under  surface  of  the  liver,  from  which  the  descrip- 
tion started. 

Changes  after  Birth. — After  birth  the  foramen  ovale  closes  and  so 
do  the  ductus  arteriosus  and  ductus  venosus,  as  well  as  the  umbilical 
vessels ;  so  that  the  two  streams  of  blood  which  arrive  at  the  right  auri- 
cle by  the  superior  and  inferior  vena  cava  respectively,  thenceforth 
mingle  in  this  cavity  of  the  heart,  and  passing  into  the  right  ventricle, 
go  by  way  of  the  pulmonary  artery  to  the  lungs,  and  through  these,  after 
purification,  to  the  left  auricle  and  ventricle,  to  be  distributed  over  the 
body.     (See  Chapter  on  Circulation.) 

The  Nervous  System. 

The  Cranial  and  Spinal  Nerves. — The  cranial  nerves  are  derived 
from  a  continuous  band,  called  the  neural  band.  They  are  formed  be- 
fore the  neural  canal  is  complete.  The  neural  band  is  made  up  of  two 
laminae  going  from  the  dorsal  edges  of  the  neural  groove  to  the  external 
epiblast.  It  becomes  separated  from  the  epiblast,  and  then  forms  a 
crest  attached  to  the  upper  surface  of  the  brain.  The  posterior  roots  of 
the  spinal  nerves  arise  as  outgrowths  of  median  processes  of  cells  from 
the  dorsal  side  of  the  spinal  cord,  which  become  attached  laterally  to  the 
spinal  cord  as  their  original  point  of  attachment  disappears.  The  ante- 
rior roots  probably  arise  from  the  ventral  part  of  the  cord  as  a  number  of 
strands  for  each  nerve.  They  appear  later  than  the  posterior  roots. 
The  rudiment  of  the  posterior  root  is  differentiated  into  a  proximal  round 
nerve  connected  to  the  cord,  a  ganglionic  portion  and  a  distal  portion. 
To  the  last  the  anterior  nerve-root  becomes  attached. 

Tlie  Spinal  Cord.— -The  spinal  cord  consists  at  first  of  the  undifferen- 
tiated epiblast  of  the  walls  of  the  neural  canal,  the  cavity  of  which  is 
large,  with  almost  parallel  sides.  The  walls  are  at  first  composed  of 
elongated  irregular  nucleated  columnar  cells,  arranged  in  a  radiate  man- 
ner. The  cavity  then  becomes  narrow  in  the  middle  and  of  an  hour-glass 
shape  (Fig.  482).  When  the  spinal  nerves  make  their  first  appearance, 
about  the  fourth  day  in  the  chick,  the  epiblastic  walls  become  differen- 
tiated into  three  parts:  (a)  the  epithelium  lining  the  central  canal;  (b)  the 


DEVELOPMENT.  697 

* 

gray  matter ;  (c)  the  external  white  matter.  The  last  is  derived  from 
the  outermost  part  of  the  epiblastic  walls  by  the  conversion  of  the  cells 
into  longitudinal  nerve-fibres.  The  fibres  being  without  any  myelin 
sheath,  are  for  a  time  gray  in  appearance.  The  white  matter  corre. 
-ponds  in  position  to  the  anterior  and  posterior  nerve-roots,  and  are  the 
anterior  and  posterior  white  columns.  It  is  at  first  a  very  thin  layer, 
but  increases  in  thickness  until  it  covers  the  whole  cord.  The  gray  mat- 
ter too  arises  from  the  cells  by  their  being  prolonged  into  fibres.  The 
change  in  the  central  cells  is  sufficiently  obvious.  The  anterior  and  pos- 
terior cornua  of  gray  matter  and  the  anterior  gray  commissure  then  ap- 
pear. The  anterior  fissure  is  formed  on  the  fifth  day  by  the  growth 
downwards  of  the  anterior  cornua  of  gray  matter  towards  the  middle 
line.  The  posterior  fissure  is  formed  later.  The  whole  cord  now  be- 
comes circular.     The  posterior  gray  commissure  is  then  formed. 

When  it  first  appears,  the  spinal  cord  occupies  the  whole  length  of  the 
medullary  canal,  but  as  development  proceeds,  the  spinal  column  grows 
more  rapidly  than  the  contained  cord,  so  that  the  latter  appears  as  if 
drawn  up  till,  at  birth,  it  is  opposite  the  third  lumbar  vertebra,  and  in 


Fig.  482.—  Diagram  of  development  of  spinal  cord;  cc,  central  canal;  af,  anterior  fissure;  p/, 
posterior  fissure;  g,  gray  matter;  ic,  white  matter.    For  further  explanation  see  text. 

the  adult  opposite  the  first  lumbar.  In  the  same  way  the  increasing  obli- 
quity of  the  spinal  nerves  in  the  neural  canal,  as  we  approach  the  lum- 
bar region,  and  the  "cauda  equina"  at  the  lower  end  of  the  cord,  are 
accounted  for. 

Brain. — We  have  seen  that  the  front  portion  of  the  medullary  canal 
is  almost  from  the  first  widened  out  and  divided  into  three  vesicles. 
From  the  anterior  vesicle  (thalamencephalon)  the  two  primary  optic 
vesicles  are  budded  off  laterally:  their  further  history  will  be  traced  in 
the  next  section.  Somewhat  later,  from  the  same  vesicle  the  rudiments 
of  the  hemispheres  appear  in  the  form  of  two  outgrowths  at  a  higher 
level,  which  grow  upwards  and  backwards.  These  form  the  prosenceph- 
alon. 

In  the  walls  of  the  posterior  (third)  cerebral  vesicle,  a  thickening  ap- 
pears (rudimentary  cerebellum)  which  becomes  separated  from  the  rest 
of  the  vesicle  by  a  deep  inflection. 

At  this  time  there  are  two  chief  curvatures  of  the  brain  (Fig.  483,  3). 
(1.)  A  sharp  bend  of  the  whole  cerebral  mass  downwards  round  the 
end  of  the  notochord,  by  which  the  anterior  vesicle,  which  was  the  high- 


Q9S 


HANDBOOK    OF    PHYSIOLOGY. 


est  of  the  three,  is  bent  downwards,  and  the  middle  one  comes  to  oc- 
cupy the  highest  position.  (2.)  A  sharp  bend,  with  the  convexity  for- 
wards, which  runs  in  from  behind  beneath  the  rudimentary  cerebellum 
separating  it  from  the  medulla. 

Thus,  five  fundamental  parts  of  the  f cetal  brain  may  be  distinguished, 


Fig.  483.— Early  stages  n  development  of  human  brain  (magnified).  1,  3,  3,  are  from  an  em- 
bryo about  seven  weeks  old;  4,  about  three  months  old ;  m,  middle  cerebral  vesicle  (mesencepha- 
lon); c, cerebellum ;  mo,  medulla  oblongata;^,  thalamencephalon;  h,  hemispheres;  i',  infundibulum; 
Fig.  3  shows  the  several  curves  which  occur  in  the  course  of  development;  Fig.  4  is  a  lateral  view, 
showing  the  great  enlargement  of  the  cerebral  hemispheres  which  have  covered  in  the  thalami, 
leaving'  the  optic  lobes,  m,  uncovered.    (Koliker.) 

N.B.— In  Fig.  2  the  line  i  terminates  in  the  right  hemisphere;  it  ought  to  be  continued  into  the 
thalamencephalon . 

which,  together,  with  the  parts  developed  from  them,  may  be  presented 
in  the  following  tabular  view: — 


Table  of  Parts  Developed  from   Fundamental  Parts  of  Brain. 


I. 


II. 


Anterior 
Primary 

Vesicle. 


Middle 
Primary 

Vesicle. 


1.  Prosencephalon. 


j  2.   Thalamencephalon 
(  (Diencephalon). 


3.   Mesencephalon. 


'Cerebral  hemispheres,  cor- 
pora striata,  corpus  callo- 
sum,  fornix,  lateral  ven- 
tricles, olfactory  bulb. 

f  Thalami       optici,        pineal 
gland  (part  of),   pituitary 
■{      body,  third  ventricle,  op- 
tic nerve  (primarily),   in- 

[     fundibulum. 
Corpora  quadrigemina,  cru- 
ra   cerebri,    aqueduct    of 
Sylvius,  optic  nerve  (sec- 
ondarily). 


DEVELOPMENT. 


.;-..:. 


III.  Posterior 
Primary 
Vesicle. 


4.  Epencephalon. 

5.  Metencephalon. 


Cerebellum,     pons    Varolii, 
anterior  part  of  fourth  ven- 
tricle. 
j  Medulla    oblongata,    fourth 
1      ventricle,  auditory  nerve. 
(Quain.) 


The  cerebral  hemispheres  grow  rapidly  upwards  and  backwards, 
while  from  their  inferior  surface  the  olfactory  bulbs  are  budded  off,  and 
the  prosencephalon,  from  which  they  spring,  remains  to  form  the  third 
ventricle  and  optic  thalami.  The  middle  cerebral  vesicle  (mesencepha- 
lon) for  some  time  is  the  most  prominent  part  of  the  foetal  brain,  and  in 
Fishes,  Amphibia,  and  Eeptiles,  it  remains  uncovered  through  life  as 
the  optic  lobes.  But  in  Birds  the  growth  of  the  cerebral  hemispheres 
thrusts  the  optic  lobes  down  laterally,  and  in  Mammalia  completely 
overlaps  them. 

In  the  lower  Mammalia  the  backward  growth  of  the  hemispheres 
ceases  as  it  were,  but  in  the  higher  groups,  such  as  the  monkeys  and 


Fig.  484.— Side  view  of  foetal  brain  at  six  months,  showing  commencement  of  formation  of  the 
principal  fissures  and  convolutions.  F,  frontal  lobe;  P,  parietal;  O,  occipital;  T,  temporal;  a  a  a, 
commencing  frontal  convolutions;  s.  Sylvian  fissure;  «',  its  anterior  division;  c,  within  it  the  central 
lobe  or  island  of  Reil;  r,  fissure  of  Rolando;  p,  perpendicular  fissure.    (R.  Wagner.) 

man,  they  grow  still  further  back,  until  they  completely  cover  in  the 
cerebellum,  so  that  on  looking  down  on  the  brain  from  above,  the  cere- 
bellum is  quite  concealed  from  view.  The  surface  of  the  hemispheres 
is  at  first  quite  smooth,  but  as  early  as  the  third  month  the  great  Syl- 
vian fissure  begins  to  be  formed  (Fig.  483,  4). 

The  next  to  appear  is  the  parieto-occipital  or  perpendicular  fissure  ; 
these  two  great  fissures,  unlike  the  rest  of  the  sulci,  are  formed  by  a 
curving  round  of  the  whole  cerebral  mass. 

In  the  sixth  month  the  fissure  of  Rolando  appears  :  from  this  time 
till  the  end  of  fcetal  life  the  brain  grows  rapidly  in  size,  and  the  convo- 
lutions appear  in  quick  succession  ;  first  the  great  primary  ones  are 
sketched  out,  then  the  secondary,  and  lastly  the  tertiary  ones  in  thesidea 
of  the  fissures.  The  commissures  of  the  brain  (anterior,  middle,  and 
posterior),  and  the  corpus  callosum,  are  developed  by  the  growth  of 
fibres  across  the  middle  line. 


700  HANDBOOK    OF    PHYSIOLOGY. 

The  Hippocampus  major  is  formed  by  the  folding  in  of  the  gray 
matter  from  the  exterior  into  the  lateral  ventricles.  The  essential  points 
in  the  structure  and  arrangement  of  the  various  parts  of  the  brain,  are 
diagrammatically  shown  in  the  two  accompanying  figures  (Figs.  483, 
484). 

The  Special  Sense  Organs. 

The  Eye. — Soon  after  the  first  three  cerebral  vesicles  have  become 
distinct  from  each  other,  the  anterior  one  sends  out  a  lateral  vesicle  from 
each  side  (primary  optic  vesicle),  which  grows  out  towards  the  free  sur- 
face, its  cavity  of  course  communicating  with  that  of  the  cerebral  vesicle 
through  the  canal  in  its  pedicle.  It  is  soon  met  and  invaginated  by  an 
in-growing  process  from  the  epiblast  (Fig.  450),  very  much  as  the  grow- 
ing tooth  is  met  by  the  process  of  epithelium  which  produces  the  enamel 
organ.  This  process  of  the  epiblast  is  at  first  a  depression  which  ulti- 
mately becomes  closed  in  at  the  edges  so  as  to  produce  a  hollow  ball, 
which  is  thus  completely  severed  from  the  epithelium  with  which  it  was 


Fig.  485.—  Longitudinal  section  of  the  primary  optic  vesicle  in  the  chick  magnified  (from 
Remak).  A,  from  an  embryo  of  sixty-five  hours;  B,  a  few  hours  later;  C,  of  the  fourth  day;  1, 
the  corneous  layer  or  epidermis,  presenting  in  A  3  the  open  depression  for  the  lens,  which  is  closed 
in  B  and  C ;  2,  the  lens  follicle  and  lens ;  5,  the  primary  optic  vesicle ,  in  A  and  B,  the  pedicle  is  shown ; 
in  C,  the  section  being  to  the  side  of  the  pedicle,  the  latter  is  not  shown;  7,  the  secondary  ocular 
vesicle  and  vitreo  us  humor. 

originally  continuous.  From  this  hollow  ball  the  crystalline  lens  is  de- 
veloped. By  the  in-growth  of  the  lens  the  anterior  wall  of  the  primary 
optic  vesicle  is  forced  back  nearly  into  contact  with  the  posterior,  and 
thus  the  primary  optic  vesicle  is  almost  obliterated.  The  cells  in  the 
anterior  wall  are  much  longer  than  those  of  the  posterior  wall;  from  the 
former  the  retina  proper  is  developed,  from  the  latter  the  retinal  pig- 
ment. 

The  cup-shaped  hollow  in  which  the  lens  is  now  lodged  is  termed  the 
secondary  optic  vesicle:  its  walls  grow  up  all  round,  leaving,  however,  a 
slit  at  the  lower  part. 

Choroidal  Fissure. — Through  this  slit  (Fig.  487),  often  termed  the 
choroidal  fissure,  a  process  of  mesoblast  containing  numerous  blood-ves- 
sels projects,  and  occupies  the  cavity  of  the  secondary  optic  vesicle  be- 
hind the  lens,  filling  it  with  vitreous  humor  and  furnishing  the  lens 
capsule   and  the   capsulo-pupillary  membrane.     This  process  in  Mam- 


DEVELOPMENT. 


7<>i 


mals  projects,  not  only  into  the  secondary  optic  vesicle,  but  also  into  the 
pedicle  of  the  primary  optic  vesicle  iuvaginating  it  for  some  distance 
from  beneath,  and  thus  carrying  up  the  arteria  centralis  retime  into  its 
permanent  position  in  the  centre  of  the  optic  nerve. 

This  invagination  of  the  optic  nerve  does  not  occur  in  birds,  and  con- 
sequently no  arteria  centralis  retinae  exists  in  them.  But  they  possess 
an  important  permanent  relic  of  the  original  protrusion  of  the  meso- 
blast  through  the  choroidal  fissure,  forming  the  pecte?i,  while  a  remnant 
of  the  same  fissure  sometimes  occurs  in  man  under  the  name  coloboma 
iridis.  The  cavity  of  the  primary  optic  vesicle  becomes  completely 
obliterated,  and  the  rods  and  cones  come  into  apposition  with  the  pig- 
ment layer  of  the  retina.  The  cavity  of  its  pedicle  disappears  and  the 
solid  optic  nerve  is  formed.  Meanwhile  the  cavity  which  existed  in  the 
centre  of  the  primitive  lens  becomes  filled  up  by  the  growth  of  fibres 
from  its  posterior  wall.     The  epithelium  of  the  cornea  is  developed  from 


Fig.  486.  Fig.  487. 

Fig.  486.— Diagrammatic  sketch  of  a  vertical  longitudinal  section  through  the  eyeball  of  a 
human  foetus  of  four  weeks.  The  section  is  a  little  to  the  side,  so  as  to  avoid  passing  through  the 
ocular  cleft;  c,  the  cuticle  where  it  becomes  later  the  corneal  epithelium;  I.  the  lens;  op,  optic 
nerve  formed  by  the  pedicle  of  the  primary  optic  vesicle;  vp,  primary  medullary  cavity  or  optic 
vesirle;  p,  the  pigment  layer  of  the  retina;  r,  the  inner  wall  forming  the  retina  proper;  vs,  second- 
ary optic  vesicle  containing  the  rudiment  of  the  vitreous  humor,     x  100.    (Kdlliker. ) 

Fig.  487'.— Transverse  vertical  section  of  the  eyeball  of  a  human  embryo  of  four  weeks.  The 
anterior  half  of  the  section  is  represented:  »r,  the  remains  of  the  cavity  of  the  primary  optic  vesi- 
cle; p,  the  inner  part  of  the  outer  layer  forming  the  retinal  pigment;  r,  the  thickened  inner  part 
Kiving  rise  to  the  columnar  and  other  structures  of  the  retina;  v,  the  commencing  vitreous  humor 
within  the  secondary  optic  vesicle ;  v',  the  ocular  cleft  through  which  the  loop  of  the  central  blood- 
vessel, a,  projects  from  below;  I,  the  lens  with  a  central  cavity.     X  100.    ( KiUliker.) 

the  epiblast,  while  the  corneal  tissue  proper  is  derived  from  the  meso- 
blast  which  intervenes  between  the  epiblast  and  the  primitive  lens  which 
was  originally  continuous  with  it.  The  sclerotic  coat  is  developed  round 
the  eye-ball  from  the  general  mesoblast  in  which  it  is  imbedded. 

The  iris  is  formed  rather  late,  as  a  circular  septum  projecting  in- 
wards, from  the  fore  part  of  the  choroid,  between  the  lens  and  the  cor- 
nea. In  the  eye  of  the  foetus  of  Mammalia,  the  pupil  is  closed  by  a 
delicate  membrane,  the  membrana  pupillari8fwhich  forms  the  front  por- 
tion of  a  highly  vascular  membrane  that,  m  the  feetus,  surrounds  the 
lens,  and  is  named  the  membrana  capsulo-pupiUaris  (Fig.   488).     It  is 


702  HANDBOOK    OF  PHYSIOLOGY. 

supplied  with  blood  by  a  branch  of  the  arteria  centralis  retina,  which 
passing  forwards  to  the  back  of  the  lens,  there  subdivides.  The  mem- 
brana  capsulo-pupillaris  withers  and  disappears  in  the  human  subject  a 
short  time  before  birth. 

The  eyelids  of  the  human  subject  and  mammiferous  animals  like 
those  of  birds,  are  first  developed  in  the  form  of  a  ring.  They  then  ex- 
tend over  the  globe  of  the  eye  until  they  meet  and  become  firmly  agglu- 


Fig.  488.— Blood-vessels  of  the  capsulo-pupillary  membrane  of  a  new-born  kitten,  magnified. 
The  drawing  is  taken  from  a  preparation  injected  by  Tiersch,  and  shows  in  the  central  part  the  con- 
vergence of  the  network  of  vessels  in  the  pupillary  membrane.    (KOUiker.) 

tiuated  to  each  other.  But  before  birth,  or  in  the  Carnivora  after  birth, 
they  again  separate. 

The  Ear. — Very  early  in  the  development  of  the  embryo  a  depres- 
sion or  iu-growth  of  the  epiblast  occurs  on  each  side  of  the  head  winch 
deepens  and  soon  becomes  a  closed  follicle.  This  primary  otic  vesicle, 
which  closely  corresponds  in  its  formation  to  the  lens  follicle  in  the  eye, 
sinks  down  to  some  distance  from  the  free  surface  ;  from  it  are  devel- 
oped the  epithelial  lining  of  the  membranous  labyrinth  of  the  internal 
ear,  consisting  of  the  vestibule  and  its  semicircular  canals  and  the  scala 
media  of  the  cochlea.  The  surrounding  mesoblast  gives  rise  to  the  vari- 
ous fibrous  bony  and  cartilaginous  parts  which  complete  and  inclose  this 
membranous  labyrinth,  the  bony  semicircular  canals,  the  walls  of  the 
cochlea  with  its  scala  vestibuli  and  scala  tympani.  In  the  mesoblast, 
between  the  primary  otic  vesicle  and  the  brain,  the  auditory  nerve  is 
gradually  differentiated  and  forms  its  central  and  peripheral  attach- 
ments to  the  brain  and  internal  ear  respectively.  According  to  some 
authorities,,  however,  it  is  said  to  take  its  origin  from  and  grow  out  of 
the  hind  brain. 

The  Eustachian  tube,  the  cavity  of  the  tympanum,  and  the  external 
auditory  passage,  are  remains  of  the  first  branchial  cleft.  The  mem- 
brana  tympani  divides  the  cavity  of  this  cleft  into  an  internal  space,  the 


DEVELOPMENT. 


703 


tympanum,  and  the  external  meatus.  The  mucous  membrane  of  the 
mouth,  which  is  prolonged  in  the  form  of  a  diverticulum  through  the 
Eustachian  tube  into  the  tympanum,  and  the  external  cutanous  system, 
come  into  relation  with  each  other  at  this  point ;  the  two  membranes 
being  separated  only  by  the  proper  membrane  of  the  tympanum. 

The  pinna  or  external  ear  is  developed  from  a  process  of  integument 
in  the  neighborhood  of  the  first  and  second  visceral  arches,  and  probably 
corresponds  to  the  gill-cover  (operculum)  in  fishes. 

The  Nose. — The  nose  originates,  like  the  eye  and  ear,  in  a  depres- 
sion of  the  superficial  epiblast  at  each  side  of  the  fronto-nasal  process 
(primary  olfactory  groove),  which  is  at  first  completely  separated  from 
the  cavity  of  the  mouth,  gradually  extends  backwards  and  downwards 
till  it  opens  into  the  mouth. 

The  outer  angles  of  the  fronto-nasal  process,  uniting  with  the  max- 
illary process  on  each  side,  convert  what  was  at  first  a  groove  into  a 
closed  canal. 

The  Alimentaky  Canal. 

The  alimentary  canal  in  the  earliest  stages  of  its  development  con- 
sists of  three  distinct  parts — the  fore  and  hind  gut  ending  blindly  at 


Fig.  489.— Outlines  of  the  form  and  position  of  the  alimentary  canal  in  successive  stages  of  its 
development.  A,  alimentary  canal,  etc.,  in  au  embryo  of  four  weeks;  B,  at  six  weeks;  C,  at  eight 
weeks;  D,  at  ten  weeks;  /,  the  primitive  lungs  connected  with  the  pharynx;  s,  the  stomach:  d,  the 
duodenum;  i,  the  small  intestine;  i,  the  large;  c,  caecum  and  vermiform  appendant;  ''■  the  rec 
Hun  ;  <l.  in  A,  the  cloaca,  a,  in  B,  the  anus  distinct  from  8  i,  the  sinus  uro-geuitnlis;  o,  the  yelk-sac; 
v  i,  the  vitello-intestinal  duct;  u,  the  urinary  bladder  and  urachus  leading  to  the  allantois;  </,  geni- 
tal ducts.    (Allen  Thomson .) 


each  end  of  the  body,  and  a  middle  segment  which  communicates  freely 
on  its  ventral  surface  wrth  the  cavity  of  the  yelk-sac  through  the  vitel- 
line or  omphalo-mesenteric  duct. 


704 


HANDBOOK    OF    PHYSIOLOGY. 


From  the  fore-gut  are  formed  the  pharynx,  oesophagus,  and  stom- 
ach ;  from  the  hind-gut,  the  lower  end  of  the  colon  and  the  rectum. 
The  mouth  is  developed  by  an  involution  of  the  epiblast  between  the 
maxillary  and  mandibular  processes,  which  becomes  deeper  and  deeper 
till  it  reaches  the  blind  end  of  the  fore-gut,  and  at  length  communicates 
freely  with  the  pharynx  by  the  absorption  of  the  partition  between  the 
two. 

At  the  other  end  of  the  alimentary  canal  the  anus  is  formed  in  a  pre- 
cisely similar  way  by  an  involution  from  the  free  surface,  which  at  length 
opens  into  the  hind-gut.  When  the  depression  from  the  free  surface 
does  not  reach  the  intestine,  the  condition  known  as  imperforate  anus 
results.  A  similar  condition  may  exist  at  the  other  end  of  the  alimen- 
tary canal  from  the  failure  of  the  involution  which  forms  the  mouth,  to 


Fig.  490. 


Fig.  491. 


Fig.  490.— First  appearance  of  the  parotid  gland  in  the  embryo  of  a  sheep. 
Fig.  491.— Lobules  of  the  parotid,  with  the  salivary  ducts,  in  the  embryo  of  the  sheep,  at  a  more 
advanced  stage. 

meet  the  fore-gut.  The  middle  portion  of  the  digestive  canal  becomes 
more  and  more  closed  in  till  its  originally  wide  communication  with  the 
yelk-sac  becomes  narrowed  down  to  a  small  duct  (vitelline).  This  duct 
usually  completely  disappears  in  the  adult,  but  occasionally  the  proxi- 
mal portion  remains  as  a  diverticulum  from  the  intestine.  Sometimes 
a  fibrous  cord  attaching  some  part  of  the  intestine  to  the  umbilicus,  re- 
mains to  represent  the  vitelline  duct.  Such  a  cord  has  been  known  to 
cause  in  after-life  strangulation  of  the  bowel  and  death. 

The  alimentary  canal  lies  in  the  form  of  a  straight  tube  close  beneath 
the  vertebral  column,  but  it  gradually  becomes  divided  into  its  special 
parts,  stomach,  small  intestine,  and  large  intestine  (Fig.  489),  and  at  the 


DEVKUU'MK.VI. 


705 


same  time  comes  to  be  suspended  in  the  abdominal  cavity  by  means  of  a 
lengthening  mesentery  formed  from  the  splanchnopleure  which  at- 
taches it  to  the  vertebral  column.  The  stomach  originally  has  the  same 
direction  as  the  rest  of  the  canal  ;  its  cardiac  extremity  being  superior, 
its  pylorus  inferior.  The  changes  of  position  which  the  alimentary 
canal  undergoes  may  be  readily  gathered  from  the  accompanying  figures 
(Fig.  489). 

Pancreas  and  Salivary  Glands. — The  principal  glands  in  connec- 
tion with  the  intestinal  canal  are  the  salivary,  pancreas,  and  the  liver. 
In  Mammalia,  each  salivary  gland  first  appears  as  a  simple  canal  with 
bud-like  processes  (Fig.  490),  lying  in  a  gelatinous  nidus  or  blastema, 
and  communicating  with  the  cavity  of  the  mouth.  As  the  development 
of  the  gland  advances,  the  canal  becomes  more  and  more  ramified,  in- 
creasing at  the  expense  of  the  blastema  in  which  it  is  still  inclosed.  The 
branches  or  salivary  ducts  constitute  an  independent  system  of  closed 


Fig.  492. 


Fig.  493. 


Fig.  492.— Diagram  of  part  of  digestive  tract  of  a  chick  04th  day).  The  black  line  represents 
hypoblast,  the  outer  shading,  raesoblast:  Ig,  lung  diverticulum,  with  expanded  end  forming  primary 
lung- vesicle ;  St,  stomach;  I.  two  hepatic  diverticula,  with  their  terminations  united  by  solid  rows 
of  hypoblast  cells;  p,  diverticulum  of  the  pancreas  with  the  vesicular  diverticula  coming  from  it. 
(Gotte.) 

Fig.  493.— Kudiments  of  the  liver  on  the  intestine  of  a  chick  at  the  fifth  day  of  incubation,  a, 
heart;  6,  intestine;  c.  diverticulum  of  the  intestine  in  which  the  liver  (d)  is  developed;  e,  part  of  the 
mucous  layer  of  the  germinal  membrane.    (Miiller.) 

tubes  (Fig.  491).  The  pancreas  is  developed  exactly  as  the  salivary 
glands,  but  is  developed  from  the  hypoblast  lining  the  intestine,  while 
the  salivary  glands  are  formed  from  the  epiblast  lining  the  mouth. 

Liver. — The  liver  is  developed  by  the  protrusion,  as  it  were,  of  a 
part  of  the  walls  of  the  fore-gut,  in  the  form  of  two  conical  hollow 
branches  which  embrace  the  common  venous  stem  (Figs.  492,  493).  The 
outer  part  of  these  cones  involves  the  omphalo-mesenteric  vein,  which 
breaks  up  in  its  interior  into  a  plexus  of  capillaries,  ending  in  venous 
trunks  for  the  conveyance  of  the  blood  to  the  heart.  The  inner  portion 
of  the  cones  consists  of  a  number  of  solid  cylindrical  masses  of  cells,  de- 
rived probably  from  the  hypoblast,  which  become  gradually  hollowed  by 
45 


706  HANDBOOK    OF   PHYSIOLOGY. 

the  formation  of  the  hepatic  ducts,  and  among  which  blood-vessels  are 
rapidly  developed.  The  gland- cells  of  the  organs  are  derived  from  the 
hypoblast,  the  connective  tissue  and  vessels  without  doubt  from  the  meso- 
blast.  The  gall-bladder  is  developed  as  a  diverticulum  from  the  he- 
patic duct.  The  spleen,  lymphatic,  and  thymus  glands  are  developed 
from  the  mesoblast :  the  thyroid  partly  also  from  the  hypoblast,  which 
grows  into  it  as  a  diverticulum  from  the  fore-gut. 

The  Eespiratory  Apparatus. 

The  lungs,  at  their  first  development,  appear  as  small  as  tubercles, 
or  diverticula  from  the  abdominal  surface  of  the  oesophagus. 

The  two  diverticula  at  first  open  directly  into  the  oesophagus,  but  as 
they  grow,  a  separate  tube  (the  future  trachea)  is  formed  at  their  point 
of  fusion,  opening  into  the  oesophagus  on  its  anterior  surface.  These 
primary  diverticula  of  the  hypoblast  of  the  alimentary  canal  send  off 
secondary  branches  into  the  surrounding  mesoblast,  and  these  again  give 


Fig.  494  illustrates  the  development  of  the  respiratory  organs,  a,  is  the  oesophagus  of  a  chick 
on  the  fourth  day  of  incubation,  with  the  rudiments  of  the  trachea  on  the  lung  of  the  left  side, 
viewed  laterally;  1,  the  inferior  wall  of  the  oesophagus;  2,  the  upper  tube  of  the  same  tube;  3,  the 
rudimentary  lung;  4,  the  stomach,  b,  is  the  same  object  seen  from  below,  so  that  both  lungs  are 
visible,  c,  shows  the  tongue  and  respiratory  organs  of  the  embryo  of  a  horse;  1,  the  tongue;  2,  the 
larynx;  3,  the  trachea;  4,  the  lungs  viewed  from  the  upper  side.    (After  Rathke.) 

off  tertiary  branches,  forming  the  air-cells.  Thus  we  have  the  lungs 
formed  ;  the  epithelium  lining  their  air-cells,  bronchi,  and  trachea 
being  derived  from  the  hypoblast,  and  all  the  rest  of  the  lung-tissue, 
nerves,  lymphatics,  and  blood-vessels,  cartilaginous  rings,  and  muscular 
fibres  of  the  bronchi  from  the  mesoblast.  The  diaphragm  is  early  de- 
veloped. 

The  Gentto-Urinary  Apparatus. 

The  Wolffian  bodies  are  organs  peculiar  to  the  embryonic  state, 
and  may  be  regarded  as  temporary,  rather  than  rudimental,  kidneys  ; 
for  although  they  seem  to  discharge  the  functions  of  these  latter  organs, 
they  are  not  developed  into  them. 

The  Wolffian  duct  makes  its  appearance  at  an  early  stage  in  the  his- 
tory of  the  embryo,  as  a  cord  running  longitudinally  on  each  side  in  the 


DEVELol'MKXT. 


m 


mass  of  mesoblast,  which  lies  just  external  to  the  intermediate  cell-mass 
{ung,  Fig.  495).  This  cord,  at  first  solid,  becomes  gradually  hollowed 
out  to  form  a  tube  (Wolffian  duct)  which  sinks  down  till  it  projects  be- 
neath the  lining  membrane  into  the  pleuro-peritoneal  cavity. 

The  primitive  tube  thus  formed  sends  off  secondary  diverticula  at 
frequent  intervals  which  grow  into  the  surrounding  mesoblast  :  tufts  of 
vessels  grow  into  the  blind  ends  of  these  tubes,  invaginating  them  and 
producing  "  Malpighian  bodies"  very  similar  in  appearance  to  those  of 
the  permanent  kidney,  which  constitute  the  substance  of  the  "Wolffian 
body.  Meanwhile  another  portion  of  mesoblast  between  the  Wolffian 
body  and  the  mesentery  projects  in  the  form  of  a  ridge,  covered  on  its 
free  surface  with  epithelium  termed  "germ,  epithelium."  From  this 
projection  is  developed  the  reproductive  gland  (ovary  or  testis  as  the 
case  may  be). 

Simultaneously,  on  the  outer  wall  of  the  Wolffian  bodv,  between  it 


da 


Fig.  495.— Transverse  of  embryo  chick  (third  day)-  mr.  rudimentary  spinal  cord;  the  primi- 
tive central  canal  has  become  constricted  in  the  middle;  ch,  notochord;  inch,  primordial  vertebral 
mass;  m,  muscle-plate;  dr,  df,  hypoblast  and  visceral  layer  of  mesoblast  lining  groove,  which  is  not 
yet  closed  in  to  form  the  intestines;  a,  o,  one  of  the  primitive  aortse;  int.  Wolffian  body;  \mg,  Wolf- 
fian duct;  vc,  vena  cardinalis;  h,  epiblast;  hp,  somatopleure  and  its  reflexion  to  form"  a/,  amniotic 
fold;  p,  pleuro-peritoneal  cavity.    (Kolliker.) 

and  the  body- wall  on  each  side,  an  involution  is  formed  from  the  pleuro- 
peritoneal  cavity  in  the  form  of  a  longitudinal  furrow,  whose  edges  soon 
close  over  to  form  a  duct  (Muller's  duct). 

All  the  above  points  are  shown  in  the  accompanying  figures,  495, 
496,  497. 

The  Wolffian  bodies,  or  temporary  kidneys,  as  they  may  be  termed, 
give  place  at  an  early  period  in  the  human  foetus  to  their  successors,  the 
permanent  kidneys,  which  are  developed  behind  them.  They  diminish 
rapidly  in  size,  and  by  the  end  of  the  third  month  have  almost  entirely 
disappeared.  In  connection,  however,  with  their  upper  part,  in  the 
male,  there  are  developed  from  a  aew  mass  of  blastema,  the  vasa  efferen- 
tia,   coni   vasculosi,  and  globus  major  of  the   epididymis;  and   thus  is 


708 


HANDBOOK    OF    PHYSIOLOGY. 


brought  about  a  direct  connection  between  the  secreting  part  of  the  tes- 
ticle and  its  duct  (Cleland,  Banks).  The  Wolffian  ducts  persist  in  the 
male,  and  are  developed  to  form  the  body  and  globus  minor  of  the  epi- 
didymis, the  vas  deferens,  and  ejaculatory  duct  on  each  side,  the  vesic- 
ulas  seminales  forming  diverticula  from  their  lower  part.  In  the  female 
a  small  relic  of  the  Wolffian  body  persists  as  the  "  parovarium  ; "  in  the 
male  a  similar  relic  is  termed  the  "organ  of  Griraldes."  The  lower  end 
of  the  Wolffian  duct  remains  in  the  female  as  the  "  duct  of  Gaertner  " 
which  descends  towards,  and  is  lost  upon,  the  anterior  wall  of  the 
vagina. 

From  the  lower  end  of  the  Wolffian  duct  a  diverticulum  grows  back 


Fig.  496.— Section  of  intermediate  cell-mass  on  the  fourth  day.  m,  mesentery;  L,  somato- 
pleural a',  germinal  epithelium,  from  which  z,  the  duct  of  Muller,  becomes  involuted;  a,  thickened 
part  of  germinal  epithelium  in  which  the  primitive  ova  O  and  o,  are  lying;  E,  modified  mesoblast, 
which  will  form  the  stroma  of  the  ovary;  WK,  Wolffian  body;  y,  Wolffian  duct,  x  160.  (Wal- 
deyer.) 


along  the  body  of  the  embryo  towards  its  anterior  extremity,  and  ulti- 
mately forms  the  ureter.  Secondary  diverticula  are  given  off  from  it 
and  grow  into  the  surrounding  blastema  of  blood-vessels  and  cells. 

Malpighian  bodies  are  formed  just  as  in  the  Wolffian  body,  by  the  in- 
vagination of  the  blind  knobbed  end  of  these  diverticula  by  a  tuft  of  ves- 
sels. This  process  is  precisely  similar  to  the  invagination  of  the  primary 
optic  vesicle  by  the  rudimentary  lens.  Thus  the  kidney  is  developed, 
consisting  at  first  of  a  number  of  separate  lobules ;  this  condition  re- 
maining throughout  life  in  many  of  the  lower  animals,  e.  g.,  seals  and 


DEVELOPMENT. 


709 


whales,  and  traces  of  this  lobulation  being  visible  in  the  human  foetus 
at  birth.  In  the  adult  all  the  lobules  are  fused  into  a  compact  solid 
•organ. 

The  suprarenal  capsules  originate  in  a  mass  of  mesoblast  just  above 
the  kidneys  ;  soon  after  their  first  appearance  they  are  very  much 
larger  than  the  kidneys  (see  Fig.  497),  but  by  the  more  rapid  growth  of 
the  latter  this  relation  is  soon  reversed. 

The  first  appearance  of  the  generative  gland  has  been  already  de- 
scribed :  for  some  time  it  is  impossible  to  determine  whether  an  ovary  or 
testis  will  be  developed  from  it ;  gradually  however  the  special  charac- 
ters belonging  to  one  of  them  appear,  and  in  either  case  the  organ  soon 


WW3, 


w  n  r 


Wf    M 


Fig.  497.— Diagram  showing1  the  relations  of  the  female  (the  left  hand  figure  ;  )  and  of  the 
male  (the  right  hand  figure  ;  )  reproductive  organs  to  the  general  plan  (the  middle  figure)  of  these 
organs  in  the  higher  vertebrata  (including  man).  CI,  cloaca;  R,  rectum;  Bl.  urinary  bladder;  **. 
ureter;  JT,  kidney;  Uh,  urethra;"  G,  genital  gland,  ovary,  or  testis;  11*.  Wolffian  hotly:  11"-/.  Wolf- 
fian duct;  M,  Miillerian  duct;  Pst,  prostate  gland ;  Cp,  Cowper's  gland;  Csp,  corpus  spongiosum; 
Cc,  corpus  cavernosum. 

In  the  female—  V,  vagina;  Ut,  uterus;  Fp,  Fallopian  tube;  Gt,  Gaertuer's  duct;  Pi;  parova- 
rium; A,  anus;  Cc,  Cap.,  clitoris. 

In  the  male.  Csp,  Cc,  penis;  Ut,  uterus  masculinis;  Vs,  vesiculasemiualis;  Vd,  vas  deferens. 
(Huxley.) 

begins  to  assume  a  relatively  lower  position  in  the  body;  the  ovaries 
being  ultimately  placed  in  the  pelvis;  while  towards  the  end  of  foetal  ex- 
istence the  testicles  descend  into  the  scrotum,  the  testicle  entering  the 
internal  inguinal  ring  in  the  seventh  month  of  foetal  life,  and  completing 
its  descent  through  the  inguinal  canal  and  external  ring  into  the  scrotum 
by  the  end  of  the  eighth  month.  A  pouch  of  peritoneum,  the  processus 
vaginalis,  precedes  it  in  its  descent,  and  ultimately  forms  the  tunica  vagi- 


710 


HANDBOOK    OF    PHYSIOLOGY. 


nalis  or  serous  covering  of  the  organ  ;  the  communication  between  the 
tunica  vaginalis  and  the  cavity  of  the  peritoneum  being  closed  only  a 
short  time  before  birth.  In  its  descent,  the  testicle  or  ovary  of  course 
retains  the  blood-vessels,  nerves,  aud  lymphatics,  which  were  supplied 
to  it  while  in  the  lumbar  region,  and  which  are  compelled  to  accompany 
it,  so  to  speak,  as  it  assumes  a  lower  position  in  the  body.  Hence  the 
explanation  of  the  otherwise  strange  fact  of  the  origin  of  these  parts  at 
so  considerable  a  distance  from  the  organ  to  which  they  are  distributed. 
Descent  of  the  Testicles  into  the  Scrotum. — The  means  by  which  the- 
descent  of  the  testicles  into  the  scrotum  is  effected  are  not  fully  and  ex- 
actly known.     It  was  formerly  believed  that  a  membranous  and  partly 


Fig.  498.— Diagram  of  the  Wolffian  bodies,  Miillerian  ducts  and  adjacent  parts  previous  to 
sexual  distinction,  as  seen  from  before,  sr,  the  suprarenal  bodies;  r,  the  kidneys;  ot,  common 
blastema  of  ovaries  or  testicles;  W,  Wolffian  bodies;  w,  Wolffian  ducts;  m,  m,  Mullerian  ducts;  g, 
genital  cord;  ug,  sinus  urogenitalis;  i,  intestine;  cl,  cloaca.    (Allen  Thomson.) 


muscular  cord,  called  the  gubernaculum  testis,  which  extends  while  the 
testicle  is  yet  high  in  the  abdomen,  from  its  lower  part,  through  the  ab- 
dominal wall  (in  the  situation  of  the  inguinal  canal)  to  the  front  of  the- 
pubes  and  lower  part  of  the  scrotum,  was  the  agent  by  the  contraction 
of  which  the  descent  was  effected.  It  is  now  generally  thought,  how- 
ever, that  such  is  not  the  case  ;  and  that  the  descent  of  the  testicle  and 
ovary  is  rather  the  result  of  a  general  process  of  development  in  these 
and  neighboring  parts,  the  tendency  of  which  is  to  produce  this  change 
in  the  relative  position  of  these  organs.     In  other  words,  the  descent  is 


DEVELOPMENT. 


711 


not  the  result  of  a  mere  mechanical  action,  by  which  the  organ  is 
dragged  clown  to  a  lower  position,  but  rather  one  change  out  of  many 
which  attend  the  gradual  development  and  re-arrangement  of  these  or- 
gans. It  may  be  repeated,  however,  that  the  details  of  the  process  by 
Avhich  the  descent  of  the  testicle  into  the  scrotum  is  effected  are  not  ac- 
curately known. 

The  homologue,  in  the  female,  of  the  gubernaculum  testis  is  a  struc- 
ture called  the  round  ligament  of  the  uterus,  which  extends  through  the 
inguinal  canal,  from  the  outer  and  upper  part  of  the  uterus  to  the  sub- 
cutaneous tissue  in  front  of  the  symphysis  pubis. 

At  a  very  early  stage  of  fcetal  life,  the  Wolffian  ducts,   ureters,  and 

Fig.  499.  Fig.  501. 


Fig.  502.  Fig.  500. 

Urinary  and  generative  organs  of  a  human  female  embryo,  measuring  3,'u  inches  in  length. 

Fig.  499.— General  view  of  these  parts;  1,  suprarenal  capsules;  2  kidneys;  8,  ovary;  4,  Fallo- 
pian tube;  5,  uterus;  6,  intestine;  7,  the  bladder. 

Fig.  500. — Bladder  and  generative  organs  of  the.  same  embryo  viewed  from  the  side;  a,  the  uri- 
nary bladder  (at  the  upper  part  is  a  portion  of  the  urachus  > ;  8,  urethra ;  3,[uterus  (with  two  coruua ) : 
4,  vagina;  5,  part  as  yet  common  to  the  vagina  and  urethra;  6,  common  orifice  of  the  urinary  and 
generative  organs;  7,  the  clitoris. 

Fig.  501.— Internal  generative  organs  of  the  same  embryo;  1.  the  uterus;  8,  the  round  ligaments: 
3.  the  Fallopian  tubes  (.formed  by  the  Miillerian  ducts);  4.  th«  ovaries;  5.  the  remains  of  the  Wolf- 
fian bodies. 

Fig.  502.—  External  generative  organs  of  the  same  embryo;  1,  the  labia  majora:  2,  the  nymphffi, 
8,  clitoris;  4,  anus.    (Muller.) 

Miillerian  ducts,  open  into  a  receptacle  formed  by  the  lower  end  of  the 
allautois,  or  rudimentary  bladder ;  and  as  this  communicates  with  the 
lower  extremity  of  the  intestine,  there  is  for  the  time,  a  common  recep- 
tacle or  cloaca  for  all  these  parts,  which  opens  to  the  exterior  of  the  body 
through  a  part  corresponding  with  the  future   anus,    an    arrangement 


712  HAITOBOOK    OF   PHYSIOLOGY. 

which  is  permanent  in  Reptiles,  Birds,  and  some  of  the  lower  Mammalia. 
In  the  hum  an  foetus,  however,  the  intestinal  portion  of  the  cloaca  is  cut 
off  from  that  which  belongs  to  the  urinary  and  generative  organs;  a  sepa- 
rate passage  or  canal  to  the  exterior  of  the  body,  belonging  to  these 
parts,  being  called  the  sinus  urog&mtalis.  Subsequently,  this  canal  is 
divided,  by  a  process  of  division  extending  from  before  backwards  or 
•  from  above  downwards,  into  a  '  pars  urinaria '  and  a  '  pars  genitalis. 
The  former,  continuous  with  urachus,  is  converted  into  the  urinary 
bladder. 

The  Fallopian  tubes,  the  uterus,  and  the  vagina  are  developed  from 
the  Mullerian  ducts  (Fig.  498,  m  and  Fig.  501)  whose  first  appearance 
has  been  already  described.  The  two  Mullerian  ducts  are  united  below 
into  a  single  cord,  called  the  genital  cord,  and  from  this  are  developed 
the  vagina,  as  well  as  the  cervix  and  the  lower  portion  of  the  body  of 
the  uterus ;  while  the  ununited  portion  of  the  duct  on  each  side  forms 
the  upper  part  of  the  uterus,  and  the  Fallopian  tube.  In  certain  cases  of 
arrested  or  abnormal  development,  these  portions  of  the  Mullerian  ducts 
may  not  become  fused  together  at  their  lower  extremities,  and  there  is 
left  a  cleft  or  horned  condition  of  the  upper  part  of  the  uterus  resem- 
bling a  condition  which  is  permanent  in  certain  of  the  lower  animals. 

In  the  male,  the  Mullerian  ducts  have  no  special  function,  and  are 
but  slightly  developed.  The  hydatid  or  Morgagni  is  the  remnant  of  the 
upper  part  of  the  Mullerian  duct.  The  small  prostatic  pouch,  uterus 
masculinus  or  sinus  pocularis,  forms  the  atrophied  remnant  of  the  dis- 
tal end  of  the  genital  cord,  and  is,  of  course,  therefore,  the  homologue, 
in  the  male,  of  the  vagina  and  uterus  in  the  female. 

The  external  parts  of  generation  are  at  first  the  same  in  both  sexes. 
The  opening  of  the  genito-urinary  apparatus  is,  in  both  sexes,  bounded 
by  two  folds  of  skin,  whilst  in  front  of  it  there  is  formed  a  penis-like 
body  surmounted  by  a  glans,  and  cleft  or  furrowed  along  its  under  sur- 
face. The  borders  of  the  furrows  diverge  posteriorly,  running  at  the 
sides  of  the  genito-urinary  orifice  internally  to  the  cutaneous  folds  just 
mentioned  (see  Figs.  499-502).  In  the  female,  this  body  becoming  re- 
tracted, forms  the  clitoris,  and  the  margins  of  the  furrow  on  its  under 
surface  are  converted  into  the  nymphas,  or  labia  minora,  the  labia  nia- 
jora  pudendae  being  constituted  by  the  great  cutaneous  folds.  In  the 
male  foetus,  the  margins  of  the  furrow  at  the  under  surface  of  the  penis 
unite  at  about  the  fourteenth  week,  and  form  that  part  of  the  urethra 
which  is  included  in  the  penis.  The  large  cutaneous  folds  form  the 
scrotum,  and  later  (in  the  eighth  month  of  development),  receive  the 
testicles,  which  descend  into  them  from  the  abdominal  cavity.  Some- 
times the  urethra  is  not  closed,  and  the  deformity  called  hypospadias 
then  results.  The  appearance  of  hermaphroditism  may,  in  these  cases, 
be  increased  by  the  retention  of  the  testes  within  the  abdomen. 


CHAPTER  XXIV.' 

ON  THE  RELATION  OF  LIFE  TO  OTHER  FORCES. 

An  enumeration  of  theories  concerning  the  nature  of  life  would  be 
beside  the  purpose  of  the  present  chapter.  They  are  interesting  as 
marks  of  the  way  in  which  various  minds  have  been  influenced  by  the 
mystery  which  has  always  hung  about  vitality;  their  destruction  is  but 
another  warning  that  any  theory  we  can  frame  must  be  considered  only 
a  tie  for  connecting  present  facts,  and  one  that  must  yield  or  break  on 
any  addition  to  the  number  which  it  is  to  bind  together. 

Before  attention  had  been  drawn  to  the  mutual  convertibility  of  the 
various  so-called  physical  forces — heat,  light,  electricity,  and  others — 
and  until  it  had  been  shown  that  these,  like  the  matter  through  which 
they  act,  are  limited  in  amount,  and  strictly  measurable;  that  a  given 
quantity  of  one  force  can  produce  a  certain  quantity  of  another  and  no 
more;  that  a  given  quantity  of  combustible  material  cau  produce  only  a 
given  quantity  of  steam,  and  this  again  only  so  much  motive  power;  it 
was  natural  that  men's  minds  should  be  satisfied  with  the  thought  that 
vital  force  was  some  peculiar  innate  power,  unlimited  by  matter,  and  al- 
together independent  of  structure  and  organization.  The  comparison  of 
life  to  a  flame  is  probably  as  early  as  any  thought  about  life  at  all.  And 
so  long  as  light  and  heat  were  thought  to  be  inherent  qualities  of  certain 
material  which  perished  utterly  in  their  production,  it  is  not  strange 
that  life  also  should  have  been  reckoned  some  strange  spirit,  pent  up  in 
the  germ,  expending  itself  in  growth  and  development,  and  finally  de- 
clining and  perishing  with  the  body  which  it  had  inhabited. 

With  the  recognition,  however,  of  a  distinct  correlation  between  the 
physical  forces,  came  as  a  natural  consequence  a  revolution  of  the  com- 
monly accepted  theories  concerning  life  also.  The  dictum,  so  long 
accepted,  that  life  was  essentially  independent  of  physical  force  began 
to  be  questioned. 

As  it  is  well-nigh  impossible  to  give  a  definition  of  life  that  shall  be 
short,  comprehensive,  and  intelligible,  it  will  be  best,  perhaps,  to  take 


1  This  chapter  is    a  reprint,  with  some  verbal  alterations,  of  an  essay  contrib 
uted  to  St.  Bartholomew's  H»* i >it, ii  Reports,  1817, 1S6D.  by  W.  Moitant  Baker. 


714  HANDBOOK    OF    PHYSIOLOGY. 

its  chief  manifestations,  and  see  how  far  these  seem  to  be  dependent  on 
other  forces  in  nature,  and  how  connected  with  them. 

Life  manifests  itself  by  Birth,  Growth,  Development,  Decline,  and 
Death;  and  an  idea  of  life  will  most  naturally  arise  by  taking  these 
events  in  succession,  and  studying  them  individually,  and  in  relation  to 
each  other. 

When  the  embryo  in  a  seed  awakes  from  that  state,  neither  life  nor 
death,  which  is  called  dormant  vitality,  and,  bursting  its  envelopes, 
begins  to  grow  up  and  develop,  it  may  be  said  that  there  is  a  birth. 
And  so,  when  the  chick  escapes  from  the  egg,  and  when  any  living  form 
is,  as  the  phrase  goes,  brought  into  the  world.  In  each  case,  however, 
birth  is  not  the  beginning  of  life,  but  only  the  continuation  of  it  under 
different  conditions.  To  understand  the  beginning  of  life  in  any  indi- 
vidual, whether  plant  or  animal,  existence  must  be  traced  somewhat  fur- 
ther back,  and  in  this  way  an  idea  gained  concerning  the  nature  of  the 
germ,  the  development  of  which  is  to  issue  in  birth. 

The  germ  may  be  denned  as  that  portion  of  the  parent  which  is  set 
apart  with  power  to  grow  up  into  the  likeness  of  the  being  from  which 
it  has  been  derived. 

The  manner  in  which  the  germ  is  separated  from  the  parent  does  not 
here  concern  us.  It  belongs  to  the  special  subject  of  generation. 
Neither  need  we  consider  apart  from  others  those  modes  of  propagation, 
as  fission  and  gemmation,  which  differ  more  apparently  than  really  from 
the  ordinary  process  typified  in  the  formation  of  the  seed  or  ovum.  In 
every  case  alike,  a  new  individual  plant  or  animal  is  a  portion  of  its  par- 
ent: it  may  be  a  mere  outgrowth  or  bud,  which,  if  separated,  can  main- 
tain an  independent  existence;  it  may  be  not  an  outgrowth,  but  simply 
a  portion  of  the  parent's  structure,  which  has  been  naturally  or  artifi- 
cially cut  off,  as  in  the  spontaneous  or  artificial  cleaving  of  a  polyp;  it 
may  be  the  embryo  of  a  seed  or  ovum,  as  in  those  cases  in  which  the  pro-, 
cess  of  multiplication  of  different  organs  has  reached  the  point  of  sepa- 
ration of  the  individual  more  or  less  completely  into  two  sexes,  the 
mutual  conjugation  of  a  portion  of  each  of  which,  the  sperm-cell  and 
the  germ-cell,  is  necessary  for  the  production  of  a  new  being.  We  are 
so  accustomed  to  regard  the  conjugation  of  the  two  sexes  as  necessary  for 
what  is  called  generation,  that  we  are  apt  to  forget  that  it  is  only  gradu- 
ally in  the  upward  progress  of  development  of  the  vegetable  and  animal 
kingdoms,  that  those  portions  of  organized  matter  which  are  to  produce 
new  beings  are  allotted  to  two  separate  individuals.  In  the  least  devel- 
oped forms  of  life,  almost  any  part  of  the  body  is  capable  of  assuming 
the  characters  of  a  separate  individual;  and  propagation,  therefore,  oc- 
curs by  fission  or  gemmation  in  some  form  or  other.  Then,  in  beings  a 
little  higher  in  rank,  only  a  special  part  of  the  body  can  become  a  sepa- 
rate being,  and  only  by  conjugation  with  another  special  part.     Still 


THE    RELATION    OF    LIFE    TO    OTHER    FORCES.  715 

there  is  but  one  parent;  and  this  hermaphrodite-form  of  generation  is 
the  rule  in  the  vegetable  and  least  developed  portion  of  the  animal  king- 
dom. At  last,  in  all  animals  but  the  lowest,  and  in  some  plants,  the 
portions  of  organized  structure  specialized  for  development  after  their 
mutual  union  into  a  new  individual,  are  found  on  two  distinct  beings, 
which  we  call  respectively  male  and  female. 

The  old  idea  concerning  the  power  of  growth  resident  in  the  germ  of 
the  new  being,  thus  formed  in  various  ways,  was  expressed  by  saying 
that  a  store  of  dormant  vitality  was  laid  up  in  it,  and  that  so  long  as  no 
decomposition  ensued,  this  was  capable  of  manifesting  itself  and  becom- 
ing active  under  the  influence  of  certain  external  conditions.  Thus,  the 
dormant  force  supposed  to  be  present  in  the  seed  or  the  egg  was  assumed 
to  be  the  primary  agent  in  effecting  development  and  growth,  and  to 
continue  in  action  during  the  whole  term  of  life  of  the  living  being,  ani- 
mal or  vegetable,  in  which  it  was  said  Lo  reside.  The  influence  of  exter- 
nal forces — heat,  light,  and  others — was  noticed  and  appreciated;  but 
these  were  thought  to  have  no  other  connection  with  vital  force  than 
that  in  some  way  or  other  they  called  it  into  action,  and  that  to  some 
extent  it  was  dependent  on  them  for  its  continuance.  They  were  not 
supposed  to  be  correlated  with  it  in  any  other  sense  than  this. 

Now,  however,  we  are  obliged  to  modify  considerably  our  notions  and 
with  them  our  terms  of  expression,  when  describing  the  origin  and  birth 
of  a  new  being. 

To  take,  as  before,  the  simplest  case — a  seed  or  egg.  We  must  sup- 
pose that  the  heat,  which  in  conjunction  with  moisture  is  necessary  for 
the  development  of  those  changes  which  issue  in  the  growth  of  a  new 
plant  or  animal,  is  not  simply  an  agent  which  so  stimulates  the  dormant 
vitality  in  the  seed  or  egg  as  to  make  it  cause  growth,  but  it  is  a  force, 
which  is  itself  transformed  into  chemical  and  vital  power.  The  embryo 
in  the  seed  or  egg  is  a  part  which  can  transform  heat  into  vital  force,, 
this  term  being  a  convenient  one  wherewith  to  express  the  power  which 
particular  structures  possess  of  growing,  developing,  and  performing 
other  actions  which  we  call  vital.1  Of  course  the  embryo  can  grow  only 
by  taking  up  fresh  material,  and  incorporating  it  with  its  own  structure, 
and  therefore  it  is  surrounded  in  the  seed  or  ovum  with  matter  sufficient 
for  nutrition  until  it  can  obtain  fresh  supplies  from  without.  The  ab. 
sorption  of  this  nutrient  matter  involves  an  expenditure  of  force  of  some 
kind  or  other,  inasmuch  as  it  implies  the  raising  of  simple  to  more  com- 
plicated forms.     Hence  the  necessity  for  heat  or  some  other  power  before 


1  The  term  "  vital  force  "  is  here  employed  for  the  sake  of  brevity.  Whether  it  is 
strictly  admissible  will  he  discussed  hereafter. 

The  general  term  fom  is  used  as  synonymous  with  what  is  now  often  termed 
energy. 


716  HANDBOOK   OF    PHYSIOLOGY. 

the  embryo  can  exhibit  any  sign  of  life.  It  would  be  quite  as  impossible 
for  the  germ  to  begin  life  without  external  force  as  without  a  supply  of 
nutrient  matter.  Without  the  force  wherewith  to  take  it,  the  matter 
would  be  useless.  The  heat,  therefore,  which  in  conjunction  with  moist- 
ure is  necessary  for  the  beginning  of  life,  is  partly  expended  as  chemical 
power,  which  causes  certain  modifications  in  the  nutrient  material  sur- 
rounding the  embryo,  e.  g.,  the  transformation  of  starch  into  sugar  in 
the  act  of  germination;  partly,  it  is  transformed  by  the  germ  itself  into 
vital  force,  whereby  the  germ  is  enabled  to  take  up  the  nutrient  material 
presented  to  it,  and  arrange  it  in  forms  characteristic  of  life.  Thus  the 
force  is  expended,  and  thus  life  begins — when  a  particle  of  organized 
matter,  which  has  itself  been  produced  by  the  agency  of  life,  begins  to 
transform  external  force  into  vital  force,  or  in  other  words  into  a  power 
by  which  it  is  enabled  to  grow  and  develop.  This  is  the  true  beginning  of 
life.  The  time  of  birth  is  but  a  particular  period  in  the  process  of  de- 
velopment at  which  the  germ,  having  arrived  at  a  fit  state  for  a  more 
independent  existence,  steps  forth  into  the  outer  world. 

The  term  "dormant  vitality,"  must  betaken  to  mean  simply  the 
existence  of  organized  matter  with  the  capacity  of  transforming  heat  or 
other  force  into  vital  or  growing  power,  when  this  force  is  applied  to  it 
under  proper  conditions. 

The  state  of  dormant  vitality  is  like  that  of  an  empty  voltaic  battery 
or  a  steam-engine  in  which  the  fuel  is  not  yet  lighted.  In  the  former 
case  no  electric  current  passes,  because  no  chemical  action  is  going  on. 
There  is  no  transformation  into  electric  force,  because  there  is  no  chemi- 
cal force  to  be  transformed.  Yet,  we  do  not  say,  in  this  instance,  that 
there  is  a  store  of  electricity  laid  up  in  a  dormant  state  in  the  battery; 
neither  do  we  say  that  a  store  of  motion  is  laid  up  in  the  steam-engine. 
And  there  is  as  little  reason  for  saying  there  is  a  store  of  vitality  in  a 
dormant  seed  or  ovum. 

Next  to  the  beginning  of  life,  we  have  to  consider  how  far  its  con- 
tinuance by  growth  and  development  is  dependent  on  external  force,  and 
to  what  extent  correlated  with  it. 

Mere  growth  is  not  a  special  peculiarity  of  living  beings.  A  crystal, 
if  placed  in  a  proper  solution,  will  increase  in  size  and  preserve  its  own 
characteristic  outline  ;  and  even  if  it  be  injured,  the  flaw  can  be  in  part 
or  wholly  repaired.  The  manner  of  its  growth,  however,  is  very  differ- 
ent from  that  of  a  living  being,  and  the  process  as  it  occurs  in  the  latter 
will  be  made  more  evident  by  a  comparison  of  the  two  cases.  The  in- 
crease of  a  crystal  takes  place  simply  by  the  laying  of  material  on  the 
surface  only,  and  is  unaccompanied  by  any  interstitial  change.  This  is, 
however,  but  an  accidental  difference.  A  much  greater  one  is  to  be 
found  in  the  fact  that  with  the  growth  of  a  crystal  there  is  no  decay  at 
the  same  time,  and  proceeding  with  it  side  by  side.  Since  there  is  no  life 


THE    RELATION    OF    LIFE    TO    OTHEE    FORCES.  717 

there  is  no  need  of  death — the  one  being  a  condition  consequent  on  the 
other.  During  the  whole  life  of  a  living  being,  on  the  other  hand, 
there  is  unceasing  change.  At  different  periods  of  existence  the  relation 
between  waste  and  repair  is  of  course  different.  In  early  life  the  addi- 
tion is  greater  than  the  loss,  and  so  there  is  growth;  the  reconstructed 
part  is  better  than  it  was  before,  and  so  there  is  development.  In  the 
decline  of  life,  on  the  contrary,  the  renewal  is  less  than  the  destruction, 
and  instead  of  development  there  is  degeneration.  But  at  no  time  is 
there  perfect  rest  or  stability. 

It  must  not  be  supposed,  therefore,  that  life  consists  in  the  capabil- 
ity of  resisting  decay.  Formerly,  when  but  little  or  nothing  was  known 
about  the  laws  which  regulate  the  existence  of  living  beings,  it  was  rea- 
sonable enough  to  entertain  such  an  idea  ;  and,  indeed,  life  was  thought 
to  be,  essentially,  a  mysterious  power  counteracting  that  tendency  to  de- 
cay which  is  so  evident  when  life  has  departed.  Now,  we  know  that  so 
far  from  life  preventing  decomposition,  it  is  absolutely  dependent  upon 
it  for  all  its  manifestations. 

The  reason  of  this  is  very  evident.  Apart  from  the  doctrine  of  cor- 
relation of  force,  it  is  of  course  plain  that  tissues  which  do  work  must 
sooner  or  later  wear  out  if  not  constantly  supplied  with  nourishment ; 
and  the  need  of  a  continual  supply  of  food,  on  the  one  hand,  and,  on  the 
other,  the  constant  excretion  of  matter  which,  having  evidently  dis- 
charged what  was  required  of  it,  was  fit  only  to  be  cast  out,  taught  this 
fact  very  plainly.  But  although,  to  a  certain  extent,  the  dependence  of 
vital  power  on  supplies  of  matter  from  without  was  recognized  and  ap- 
preciated, the  true  relation  between  the  demand  and  supply  was  not  un- 
til recently  thoroughly  grasped.  The  doctrine  of  the  correlation  of 
vital  with  other  forces  was  not  understood. 

To  make  this  more  plain,  it  will  be  well  to  take  an  instance  of  trans- 
formation of  force  more  commonly  known  and  appreciated.  In  the 
steam-engine  a  certain  amount  of  force  is  exhibited  as  motion,  and  the 
immediate  agent  in  the  production  of  this  is  steam,  which  again  is  the 
result  of  a  certain  expenditure  of  heat.  Thus,  heat  is  in  this  instance 
said  to  be  transformed  into  motion,  or,  in  other  language,  one — molecu- 
lar— mode  of  motion,  heat,  is  made  to  express  itself  by  another — me- 
chanical— mode,  ordinary  movement.  But  the  heat  which  produced  the 
vapor  is  itself  the  product  of  the  combustion  of  fuel,  or,  in  other  words, 
it  is  the  correlated  expression  of  another  force — chemical,  namely,  that 
affinity  of  carbon  and  hydrogen  for  oxygen  which  is  satisfied  in  the  act 
of  combustion.  Again,  the  production  of  light  and  heat  by  the  burning 
of  coal  and  wood  is  only  the  giviug  out  again  of  that  heat  and  light  of 
the  sun  which  were  used  in  their  production.  For,  as  it  need  scarcely 
be  said,  it  is  only  by  means  of  these  solar  forces  that  the  leaves  of  plants 
can  decompose  carbonic  acid,  etc  ,  and  thereby  provide  material  for  the 


TLB  HANDBOOK   OF   PHYSIOLOGY. 

construction  of  woody  tissue.  Thus,  coal  and  wood  being  products  of 
the  expenditure  of  force,  must  be  taken  to  represent  a  certain  amount 
of  2)0 wer  ;  and,  according  to  the  law  of  the  correlation  of  forces,  must 
be  capable  of  yielding,  in  some  shape  or  other,  just  so  much  as  was  exer- 
cised in  their  formation.  The  amount  of  force  requisite  for  rending 
asunder  the  elements  of  carbonic  acid  is  exactly  that  amount  which  will 
again  be  manifested  when  they  clash  together  again. 

The  sun,  then,  really,  is  the  prime  agent  in  the  movement  of  the 
steam-engine,  as  it  is  indeed  in  the  production  of  nearly  all  the  power 
manifested  on  this  globe.  In  this  particular  instance,  speaking  roughly, 
'its  light  and  heat  are  manifested  successively  as  vital  and  chemical 
force  in  the  growth  of  plants,  as  heat  and  light  again  in  the  burning 
fuel,  and  lastly  by  the  piston  and  wheels  of  the  engine  as  motive  power. 
We  may  use  the  term  transformation  of  force  if  we  will,  or  say  that 
throughout  the  cycle  of  changes  there  is  but  one  force  variously  mani- 
festing itself.  It  matters  not,  so  that  we  keep  clearly  in  view  the  no- 
tion that  all  force,  so  far  at  least  as  our  present  knowledge  extends,  is 
but  a  representative,  it  may  be  in  the  same  form  or  another,  of  some 
previous  force,  and  incapable  like  matter  of  being  created  afresh,  excej)t 
l>y  the  Creator.  Much  of  our  knowledge  on  this  subject  is  of  course  con- 
fined to  ideas,  and  governed  by  the  words  with  which  we  are  compelled 
to  express  them,  rather  than  to  actual  things  or  facts;  and  probably  the 
term  force  will  soon  lose  the  signification  which  we  now  attach  to  it. 
What  is  now  known,  however,  about  the  relation  of  one  force  to  another, 
is  not  sufficient  for  the  complete  destruction  of  old  ideas  ;  and,  there- 
fore, in  applying  the  examples  of  transformation  of  physical  force  to  the 
explanation  of  vital  phenomena,  we  are  compelled  still  to  use  a  vocabu- 
lary which  was  framed  for  expressing  many  notions  now  obsolete. 

The  dependence  of  the  lowest  kind  of  vital  existence  on  external 
force,  and  the  manner  in  which  this  is  used  as  a  means  whereby  life  is 
manifested,  have  been  incidentally  referred  to  more  than  once  when  de- 
scribing the  origin  of  vegetable  tissues.  The  main  functions  of  the 
vegetable  kingdom  are  construction,  and  the  perpetuation  of  the  race ; 
and  the  use  which  is  made  of  external  physical  force  is  more  simple  than 
in  animals.  The  transformation  indeed  which  is  effected,  while  much 
less  mysterious  than  in  the  latter  instance,  forms  an  interesting  link  be- 
tween animal  and  crystalline  growth. 

The  decomposition  of  carbonic  acid  or  ammonia  by  the  leaves  of 
plants  may  be  compared  to  that  of  water  by  a  galvanic  current.  In  both 
cases  a  force  is  applied  through  a  special  material  medium,  and  the  re- 
sult is  a  separation  of  the  elements  of  which  each  compound  is  formed. 
On  the  return  of  the  elements  to  their  original  state  of  union,  there  will 
be  the  return  also  in  some  form  or  other  of  the  force  which  was  used  to 
separate  them.     Vegetable  growth,   moreover,  with  which  we  are  now 


THE    RELATION    OF   LIFE    TO   OTHER    FORCES.  719 

specially  concerned,  resembles  somewhat  the  increase  of  unorganized 
matter.  The  accidental  difference  of  its  being  in  one  case  superficial 
and  in  the  other  interstitial,  is  but  little  marked  in  the  process  as  it  oc- 
curs in  the  more  permanent  parts  of  vegetable  tissues.  The  layers  of 
lignine  are  in  their  arrangement  nearly  as  simple  as  those  of  a  crystal, 
and  almost  or  quite  as  lifeless.  After  their  deposition,  moreover,  they 
undergo  no  further  change  than  that  caused  by  the  addition  of  fresh 
matter,  and  hence  they  are  not  instances  of  that  ceaseless  waste  and  re- 
pair which  have  been  referred  to  as  so  characteristic  of  the  higher  forms 
living  tissue.  There  is,  however,  no  contradiction  here  of  the  axiom, 
that  where  there  is  life  there  is  constant  change.  Those  parts  of  a  vege- 
table organism  in  which  active  life  is  going  on  are  subject,  like  the  tis- 
sues of  animals,  to  constant  destruction  and  renewal.  But,  in  the  more 
permanent  parts,  life  ceases  with  deposition  and  construction.  Addi- 
tion of  fresh  matter  may  occur,  and  so  may  decay  also  of  that  which  is 
already  laid  down,  but  the  two  processes  are  not  related  to  each  other, 
and  not,  as  in  living  parts  inter-dependent.  Hence  the  change  is  not  a 
vital  one. 

The  acquirement  in  growth,  moreover,  of  a  definite  shape  in  the  case 
of  a  tree,  is  no  more  admirable  or  mysterious  than  the  production  of  a 
crystal.  That  chloride  of  sodium  should  naturally  assume  the  form  of 
a  cube  is  as  inexplicable  as  that  an  acorn  should  grow  into  an  oak,  or  an 
ovum  into  a  man.  "When  we  learn  the  cause  in  the  one  case,  we  shall 
probably  in  the  other  also. 

There  is  nothing,  therefore,  in  the  products  of  life's  more  simple 
forms  that  need  make  us  start  at  the  notion  of  their  being  the  products 
of  only  a  special  transformation  of  ordiuary  physical  force,  and  we  can- 
not doubt  that  the  growth  and  development  of  animals  obey  the  same 
general  laws  that  govern  the  formation  of  plants.  The  connecting  links 
between  them  are  too  numerous  for  the  acceptance  of  any  other  supposi- 
tion. Both  kingdoms  alike  are  expressions  of  vital  force,  which  is  itself 
but  a  term  for  a  special  transformation  of  ordinary  physical  force.  The 
mode  of  the  transformation  is,  indeed,  mysterious,  but  so  is  that  of  heat 
into  light,  or  of  either  into  mechanical  motion  or  chemical  affinity.  All 
forms  of  life  are  as  absolutely  dependent  on  external  physical  force  as  a 
fire  is  dependent  for  its  continuance  on  a  supply  of  fuel  ;  and  there  is  as 
much  reason  to  be  certain  that  vital  force  is  an  expression  or  representa- 
tion of  the  physical  forces,  especially  heat  and  light,  as  that  these  are  the 
correlates  of  some  force  or  other  which  has  acted  or  is  acting  on  the  sub- 
stances which,  as  we  say,  produce  them. 

In  the  tissues  of  plants,  as  just  said,  there  is  but  little  change,  ex- 
cept such  as  is  produced  by  additions  of  fresh  matter.  That  which  is 
once  deposited  alters  but  little ;  or,  if  the  part  be  transient  and  easily 
perishable,  the  alteration  is  only  or  chiefly  one  produced  by  the  ordinary 


720  HANDBOOK    OF   PHYSIOLOGY. 

process  of  decay.  Little  or  no  force  is  manifested;  or,  if  it  be,  it  is  only 
the  heat  of  the  slow  oxidation  whereby  the  structure  again  returns  to  in- 
organic shape.  There  is  no  special  transformation  of  force  to  which  the 
term  vital  can  be  applied.  With  construction  the  chief  end  of  vegetable 
existence  has  been  attained,  and  the  tissue  formed  represents  a  store  of 
force  to  be  used,  but  not  by  the  being  which  laid  it  up.  The  labors  of 
the  vegetable  world  are  not  for  itself  but  for  animals.  The  power  laid 
up  by  the  one  is  spent  by  the  other.  Hence  the  reason  that  the  constant 
change,  which  is  so  great  a  character  of  life,  is  comparatively  but  little 
marked  in  plants.  It  is  present,  but  only  in  living  portions  of  the  or- 
ganism, and  in  these  it  is  but  limited.  In  a  tree  the  greater  part  of  the 
tissues  may  be  considered  dead  ;  the  only  change  they  suffer  is  that 
fresh  matter  is  piled  on  to  them.  They  are  not  the  seat  of  any  trans- 
formation of  force,  and  therefore,  although  their  existence  is  the  result 
of  living  action,  they  do  not  themselves  live.  Force  is,  so  to  speak,  laid 
lip  in  them,  but  they  do  not  themselves  spend  it.  Those  portions  of  a 
vegetable  organism  which  are  doing  active  vital  work — which  are  using 
the  sun's  light  and  heat,  as  a  means  whereby  to  prepare  building  mate- 
rial, are,  however,  the  seat  of  unceasing  change.  Their  existence  as  living 
tissue  depends  upon  this  fact — upon  their  capability  of  perishing  and 
being  renewed. 

And  this  leads  to  the  answer  to  the  question,  What  is  the  cause  of 
the  constant  change  which  occurs  in  the  living  parts  of  animals  and 
vegetables,  which  is  so  invariable  an  accompaniment  of  life,  that  we 
refuse  the  title  of  "living"  to  parts  not  attended  by  it  ?  It  is  because 
all  manifestations  of  life  are  exhibitions  of  power,  and  as  no  power  can  be 
originated  by  us:  as,  according  to  the  doctrine  of  correlation  of  force,  all 
power  is  but  the  representative  of  some  previous  force  in  the  same  or 
another  form,  so,  for  its  production,  there  must  be  expenditure  and 
change  somewhere  or  other.  For  the  vital  actions  of  plants  the  light 
and  heat  of  the  sun  are  nearly  or  quite  sufficient,  and  there  is  no  need  of 
expenditure  of  that  store  of  force  which  is  laid  up  in  themselves  ;  but 
with  animals  the  case  is  different.  They  cannot  directly  transform  the 
solar  forces  into  vital  power  ;  they  must  seek  it  elsewhere.  The  great 
use  of  the  vegetable  kingdom  is  therefore  to  store  up  power  in  such  a 
form  that  it  can  be  used  by  animals  ;  that  so,  when  in  the  bodies  of  the 
latter,  vegetable  organized  material  returns  to  an  inorganic  condition,  it 
may  give  out  force  in  such  a  manner  that  it  can  be  transformed  by  ani- 
mal tissues,  and  manifested  variously  by  them  as  vital  power. 

Hence,  then,  we  must  consider  the  waste  and  repair  attendant  on 
living  growth,  and  development  as  something  more  than  these  words, 
taken  by  themselves,  imply.  The  waste  is  the  return  to  a  lower  from  a 
higher  form  of  matter  ;  and,  in  the  fall,  force  is  manifested.  This 
force,  when  specially  transformed  by  organized  tissues,  we  call  vital.    In 


THE    RELATION    OF    LIFE    TO    OTHER    FORCES.  721 

the  repair,  force  is  laid  up.  The  analogy  with  ordinary  transmutations 
of  physical  force  is  perfect.  By  the  expenditure  of  heat  in  a  particular 
manner  a  weight  can  be  raised.  By  its  fall  heat  is  returned.  The  molec- 
ular motion  is  but  the  expression  in  another  form  of  the  mechanical. 
So  with  life.  There  is  constant  renewal  and  decay,  because  it  is  only  so 
that  vital  activity  can  take  place.  The  renewal  must  be  something  more 
than  replacement,  however,  as  the  decay  must  be  more  than  simple  me- 
chanical loss.  The  idea  of  life  must  include  both  storing  up  of  force, 
and  its  transformation  in  the  expenditure. 

Hence  we  must  be  careful  not  to  confound  the  mere  preservation  of 
individual  form  under  the  circumstances  of  concurrent  waste  and  repair, 
with  the  essential  nature  of  vitality. 

Life,  in  its  simplest  form,  has  been  happily  expressed  by  Savory  as  a 
state  of  dynamical  equilibrium,  since  one  of  its  most  characteristic  fea- 
tures is  continual  decay,  yet  with  maintenance  for  the  individual  by 
equally  constant  repair.  Since,  then,  in  the  preservation  of  the  equilib- 
rium there  is  ceaseless  change,  it  is  not  static  equilibrium  but  dynam- 
ical. 

Care  must  be  taken,  however,  not  to  accept  the  term  in  too  strict  a 
sense,  and  not  to  confound  that  which  is  but  a  necessary  attendant  on 
life  with  life  itself.  For,  indeed,  strictly,  there  is  no  preservation  of 
equilibrium  during  life.  Each  vital  act  is  an  advance  towards  death. 
We  are  accustomed  to  make  use  of  the  terms  growth  and  development  in 
the  sense  of  progress  in  one  direction,  and  the  words  decline  and  decay 
with  an  opposite  signification,  as  if,  like  the  ebb  of  the  tide,  there  were 
after  maturity  a  reversal  of  life's  current.  But,  to  use  an  equally  old 
comparison,  life  is  really  a  journey  always  in  one  direction.  It  is  an 
ascent,  more  and  more  gradual  as  the  summit  is  approached,  so  gradual 
that  it  is  impossible  to  say  when  development  ends  and  decline  begins. 
But  the  descent  is  on  the  other  side.  There  is  no  perfect  equilibrium, 
no  halting,  no  turning  back. 

The  term,  therefore,  must  be  used  with  only  a  limited  signification. 
There  is  preservation  of  the  individual,  yet,  although  it  may  seem  a 
paradox,  not  of  the  same  individual.  A  man  at  one  period  of  his  life 
may  retain  not  a  particle  of  the  matter  of  which  formerly  he  was  com- 
posed. The  preservation  of  a  living  being  during  growth  and  develop- 
ment is  more  comparable,  indeed,  to  that  of  a  nation,  than  of  an  indi- 
vidual as  the  term  is  popularly  understood.  The  elements  of  which  it 
is  made  up  fulfil  a  certain  work  the  traditions  of  which  were  handed 
down  from  their  predecessors,  and  then  pass  away,  leaving  the  same  leg- 
acy to  those  that  follow  them.  The  individuality  is  preserved,  but,  like 
all  things  handed  down  by  tradition,  its  fashion  changes,  until  at  last, 
perhaps,  scarce  any  likeness  to  the  original  can  be  discovered.  Or,  as  it 
sometimes  happens,  the  alterations  by  time  are  so  small  that  we  wonder, 
46 


^22  HANDBOOK    OF    PHYSIOLOGY. 

not  at  the  change,  but  the  want  of  it.  Yet,  in  both  cases  alike,  the  in- 
dividuality is  preserved,  not  by  the  same  individual  elements  throughout, 
but  by  a  succession  of  them. 

Again,  concurrent  waste  and  repair  do  not  imply  of  necessity  the  ex- 
istence of  life.  It  is  true  that  living  beings  are  the  chief  instances  of  the 
simultaneous  occurrence  of  these  things.  But  this  happens  only  because 
the  conditions  under  which  the  functions  of  life  are  discharged  are  the 
principal  examples  of  the  necessity  for  this  unceasing  and  mingled  de- 
struction and  renewal.  They  are  the  chief,  but  not  the  only  instances 
of  this  curious  conjunction. 

A  theoretical  case  will  make  this  plain.  Suppose  an  instance  of  some 
permanent  structure,  say  a  marble  statue.  If  we  imagine  it  to  be 
placed  under  some  external  conditions  by  which  each  particle  of  its  sub- 
stance should  waste  and  be  replaced,  yet  with  maintenance  of  its  original 
size  and  shape,  we  obtain  no  idea  of  life.  There  is  waste  and  renewal, 
with  preservation  of  the  individual  form,  but  no  vitality.  And  the 
reason  is  plain.  With  the  waste  of  a  substance  like  carbonate  of  calci- 
um whose  attractions  are  satisfied,  there  would  be  no  evolution  of  force  ; 
and  even  if  there  were,  no  structure  is  present  with  the  power  to  trans- 
form or  manifest  anew  any  power  which  might  be  evolved.  With  the 
repair,  likewise,  there  would  be  no  storing  of  force.  The  part  used  to 
make  good  the  loss  is  not  different  from  that  which  disappeared.  There 
is  therefore  neither  storing  of  force,  nor  its  transformation,  nor  its  ex- 
penditure ;  and  therefore  there  is  no  life. 

But  real  examples  of  the  preservation  of  an  individual  substance 
under  the  circumstances  of  constant  loss  and  renewal  may  be  found,  yet 
without  any  semblance  in  them  of  life. 

Chemistry,  perhaps,  affords  some  of  the  neatest  and  best  examples  of 
this.  One,  suggested  by  Shepard,  seems  particularly  apposite.  It  is 
the  case  of  trioxide  of  nitrogen  N203  in  the  preparation  of  sulphuric 
acid.  The  gas  from  which  this  acid  is  obtained  is  sulphur  dioxide,  and 
the  addition  of  an  equivalent  of  oxygen  and  the  combination  of  the 
resulting  sulphur  trioxide  (S03)  with  water  (H20)  is  all  that  is  required. 
Thus  : 

SO,         +         0         +  H20    =        H2S04 

Sulph.  dioxide  :    Oxygen  :  Water  —  Sulphuric  Acid. 

Sulphur  dioxide,  however,  cannot  take  the  necessary  oxygen  directly 
from  the  atmosphere,  but  it  can  abstract  it  from  trioxide  of  nitrogen 
(N203),  when  the  two  gases  are  mingled.  The  trioxide,  accordingly,  by 
continually  giving  up  an  equivalent  of  oxygen  to  an  equivalent  of  sul- 
phur dioxide,  causes  the  formation  of  sulphuric  acid,  at  the  same  time 
that  it  retains  its  composition  by  continually  absorbing  a  fresh  quantity 
of  oxygen  from  the  atmosphere. 


THE    RELATION    OF    LIFE    TO    OTHER    FORCES.  723 

In  this  instance,  then,  there  is  constant  waste  and  repair,  yet  with- 
out life.  And  here  an  objection  cannot  be  raised,  as  it  might  be  to  the 
preceding  example,  that  both  the  destruction  and  repair  come  from 
without,  and  are  not  dependent  on  any  inherent  qualities  of  the  sub- 
stance with  which  they  have  to  do.  The  waste  and  renewal  in  the  last- 
named  example  are  strictly  dependent  on  the  qualities  of  the  chemical 
compound  which  is  subject  to  them.  Jt  has  but  to  be  placed  in  appro- 
priate conditions,  and  destruction  and  repair  will  continue  indefinitely. 
Force,  too,  is  manifested,  but  there  is  nothing  present  which  can  trans- 
form it  into  vital  shape,  and  so  there  is  no  life. 

Hence,  our  notion  of  the  constant  decay  which,  together  with  repair, 
takes  place  throughout  life,  must  be  not  confined  to  any  simply  mechan- 
ical act.  It  must  include  the  idea,  as  before  said,  of  laying  up  of  force, 
and  its  expenditure — its  transformation  too,  in  the  act  of  being  ex- 
pended. 

The  growth,  then,  of  an  animal  or  vegetable,  implies  the  expenditure 
of  physical  force  by  organized  tissue,  as  a  means  whereby  fresh  matter  is 
added  to  and  incorporated  with  that  already  existing.  In  the  case  of  the 
plant  the  force  used,  transformed,  and  stored  up,  is  almost  entirely  de- 
rived from  external  sources;  the  material  used  is  inorganic.  The  result 
is  a  tissue  which  is  not  intended  for  expenditure  by  the  individual  which 
lias  accumulated  it.  The  force  expended  in  growth  by  animals,  on  the 
other  hand,  cannot  be  obtained  directly  from  without.  For  them  a  sup- 
ply of  force  is  necessary  in  the  shape  of  food  derived  directly  or  indi- 
rectly from  the  vegetable  kingdom.  Part  of  this  force-containing  food 
is  expended  as  fuel  for  the  production  of  power  ;  and  the  latter  is  used 
as  a  means  wherewith  to  elaborate  another  portion  of  the  food,  and  in- 
corporate it  as  animal  structure.  Unlike  vegetable  structure,  however, 
animal  tissues  are  the  seat  of  constant  change,  because  their  object  is 
not  the  storing  up  of  power,  but  its  expenditure  ;  so  there  must  be  con- 
stant waste  ;  and  if  this  happen,  then  for  the  continuance  of  life  there 
must  be  equally  constant  repair.  But,  as  before  said,  in  early  life  the 
repair  surpasses  the  loss,  and  so  there  is  growth.  The  part  repaired  is 
better  than  before  the  loss,  aud  thus  there  is  development. 

The  definite  limit  which  has  been  imposed  on  the  duration  of  life 
has  been  already  incidentally  referred  to.  Like  birth,  growth,  aud  de- 
velopment, it  belongs  essentially  to  living  beings  only.  Dead  structures 
and  those  which  have  never  lived  are  subject  to  change  and  destruction, 
but  decay  in  them  is  uncertain  in  its  beginning  and  continuance.  It  de- 
pends almost  entirely  on  external  conditions,  and  differs  altogether 
from  the  decline  of  life.  The  decline  and  death  of  living  beings  are  as 
definite  in  their  occurrence  as  growth  and  development.  Like  these  they 
may  be  hastened  or  stayed,  especially  in  the  lower  forms  of  life,  by  vari- 
ous influences  from  without  ;  but  the  putting  off  of  decline  must  be  the 


724  HANDBOOK    OF   PHYSIOLOGY. 

putting  off  also  of  so  much  life  ;  and,  apart  from  disease,  the  reverse 
is  true  also.  A  living  being  starts  on  its  career  with  a  certain  amount 
of  work  to  do — varying  infinitely  in  different  individuals,  but  for  each 
well-defined.  In  the  lowest  members  of  both  the  animal  and  vegetable 
creation  the  progress  of  life  in  any  given  time  seems  to  depend  almost 
entirely  on  external  circumstances  ;  and  at  first  sight  it  seems  almost 
as  if  these  lowly-formed  organisms  were  but  the  sport  of  the  surrounding 
elements.  But  it  is  only  so  in  appearance,  not  in  reality.  Each  act  of 
their  life  is  so  much  expended  of  the  time  and  work  allotted  to  them  ; 
and  if,  from  absence  of  those  surrounding  conditions  under  which  alone 
life  is  possible,  their  vitality  is  stayed  for  a  time,  it  again  proceeds  on 
the  renewal  of  the  necessary  conditions,  from  that  point  which  it  had 
already  attained.  The  amount  of  life  to  be  manifested  by  any  given  in- 
dividual is  the  same,  whether  it  takes  a  day  or  a  year  for  its  expenditure. 
Life  may  be  of  course  at  any  moment  interrupted  altogether  by  disease 
and  death.  But  supposing  it,  in  any  individual  organism,  to  run  its 
natural  course,  it  will  attain  but  the  same  goal,  whatever  be  its  rate  of 
movement.  Decline  and  death,  therefore,  are  but  the  natural  termina- 
tions of  life ;  they  form  part  of  the  conditions  on  which  vital  action 
begins  ;  they  are  the  end  towards  which  it  naturally  tends.  Death,  not 
by  disease  or  injury,  is  not  so  much  a  violent  interruption  of  the  course 
of  life,  as  the  attainment  of  a  distant  object  which  was  in  view  from  the 
commencement. 

In  the  period  of  decline,  as  during  growth,  life  consists  in  continued 
manifestations  of  transformed  physical  force  ;  and  there  is  of  necessity 
the  same  series  of  changes  by  which  the  individual,  though  bit  by  bit 
perishing,  yet  by  constant  renewal  retains  its  entity.  The  difference,  as 
has  been  more  than  once  said,  is  in  the  comparative  extent  of  the  loss 
and  reproduction.  In  decline  there  is  not  perfect  replacement  of  that 
which  is  lost.  Eepair  becomes  less  and  less  perfect.  It  does  not  of 
necessity  happen  that  there  is  any  decrease  of  the  quantity  of  material 
added  in  the  place  of  that  which  disappears.  But  although  the  quantity 
may  not  be  lessened,  and  may  indeed  absolutely  increase,  it  is  not  per- 
fect as  material  for  repair,  and  although  there  may  be  no  wasting,  there 
is  degeneration. 

No  definite  period  can  be  assigned  as  existing  between  the  end  of  de- 
velopment and  the  beginning  of  decline,  and  chiefly  because  the  two 
processes  go  on  side  by  side  in  different  parts  of  the  same  organism. 
The  transition  as  a  whole  is  therefore  too  gradual  for  appreciation.  But, 
after  some  time,  all  parts  alike  share  in  the  tendency  to  degeneration; 
until  at  length,  being  no  longer  able  to  subdue  external  force  to  vital 
shape,  they  die  ;  and  the  elements  of  which  they  are  composed  simply 
employ  what  remnant  of  power,  in  the  shape  of  chemical  affinity,  is  still 
left  in  them,  as  a  means  whereby  they  may  go  back  to  the  inorganic 


THE    RELATION    OF    LIFE    TO    OTHER    FORCES.  725 

world.  Of  course  the  same  process  happens  constantly  during  life  ;  but 
in  death  the  place  of  the  departing  elements  is  not  taken  by  others. 

Here,  then,  a  sharp  boundary  line  is  drawn  where  oue  kind  of  action 
stops  and  the  other  begins  ;  where  physical  force  ceases  to  be  mani- 
fested except  as  physical  force,  and  where  no  further  vital  transforma- 
tion takes  place,  or  can  in  the  body  ever  do  so.  For  the  notion  of  death 
must  include  the  idea  of  impossibility  of  revival,  as  a  distinction  from 
that  state  of  what  is  called  "  dormant  vitality,'5  in  which,  although  there 
is  no  life,  there  is  capability  of  living.  Hence  the  explanation  of  the 
difference  between  the  effect  of  appliance  of  external  force  in  the  two 
cases.  Take,  for  examples,  the  fertile  but  not  yet  living  egg,  and  the 
barren  or  dead  one.  Every  application  of  force  to  the  one  must  excite 
move  in  the  direction  of  development  ;  the  force,  if  used  at  all,  is  trans- 
formed by  the  germ  into  vital  energy,  or  the  power  by  which  it  can 
gather  up  and  elaborate  the  materials  for  nutrition  by  which  it  is  sur- 
rounded. Hence  its  freedom  throughout  the  brooding  time  from  putre- 
faction.  In  the  other  instance,  the  appliance  of  force  excites  only 
degeneration  ;  if  transformed  at  all,  it  is  only  into  chemical  force, 
whereby  the  progress  of  destruction  is  hastened  ;  hence  it  soon  rots.  To 
the  one  heat  is  the  signal  for  development,  to  the  other  for  decay.  By 
one  it  is  taken  up  and  manifested  anew,  and  in  a  higher  form  ;  to  the 
other  it  gives  the  impetus  for  a  still  quicker  fall. 

Life,  then,  does  not  stand  alone.  It  is  but  a  special  manifestation  of 
transformed  force.  "  But  if  this  be  so,"  it  may  be  said — "  if  the  resem- 
blance of  life  to  other  forces  be  great,  are  not  the  differences  still 
greater  ?  " 

At  the  first  glance,  the  distinctions  between  living  organized  tissue 
and  inorganic  matter  seem  so  great  that  the  difficulty  is  in  finding  a  like- 
ness. And  there  is  no  doubt  that  these  wide  differences  in  both  out- 
ward configuration  and  intimate  composition  have  been  mainly  the 
causes  of  the  delay  in  the  recognition  of  the  claims  of  life  to  a  place 
among  other  forces.  And  reasonably  enough.  For  the  notion  that  a 
plant  or  an  animal  can  have  any  kind  of  relationship  in  the  discharge  of 
its  functions  to  a  galvanic  battery  or  a  steam  engine  is  sufficiently  start- 
ling to  the  most  credulous.     But  so  it  has  been  proved  to  be. 

Among  the  distinctions  between  living  and  unorganized  matter,  that 
which  includes  differences  in  structure  and  proximate  chemical  compo- 
sition has  been  always  reckoned  a  great  one.  The  very  terms  organic 
and  inorganic  were,  until  quite  recently,  almost  synonymous  with  those 
which  implied  the  influence  of  life  and  the  want  of  it.  The  science  of 
chemistry,  however,  is  a  great  leveller  of  artificial  distinctions,  and 
many  complex  substances  which,  it  was  supposed,  could  not  be  formed 
without  the  agency  of  life  can  be  now  made  directly  from  their  elements 
or  from  very  simple   combinations  of   these.     The  number  of  complex 


726  HANDBOOK    OF    PHYSIOLOGY. 

substances  so  formed  artificially  is  constantly  increasing;  and  there- 
seems  to  be  no  reason  for  doubting  that  even  such  as  albumen,  gelatin, 
and  the  like  will  be  ultimately  produced  without  the  intermediation  of 
living  structure. 

The  formation  of  the  latter,  such  an  organized  structure  for  instance 
as  a  cell  or  a  muscular  fibre,  is  a  different  thing  altogether.  There  is  at 
present  no  reason  for  believing  that  such  will  ever  be  formed  by  artificial 
means;  and,  therefore,  among  the  peculiarities  of  living  force-transform- 
ing agents,  must  be  reckoned  as  a  great  and  essential  one,  a  special  inti- 
mate structure,  apart  from  mere  ultimate  or  proximate  chemical  com- 
position, to  which  there  is  no  close  likeness  in  any  artificial  apparatus, 
even  the  most  complicated.  This  is  the  real  distinction,  as  regards  com- 
position, between  a  living  tissue  and  an  inorganic  machine;  namely,  the 
difference  between  the  structural  arrangement  by  which  force  is  trans- 
formed and  manifested  anew.  The  fact  that  one  agent  for  transforming 
force  is  made  of  albumen  or  the  like,  and  another  of  zinc  or  iron,  is  a 
great  distinction,  but  not  so  essential  or  fundamental  an  one  as  the  differ- 
ence in  mechanical  structure  and  arrangement. 

In  proceeding  to  consider  the  difference  between  what  may  be  called 
the  transformation-products  of  living  tissue,  and  of  an  artificial  machine, 
it  will  be  well  to  take  one  of  the  simple  cases  first — the  production  of 
mechanical  motion;  and  especially  because  it  is  so  common  in  both. 

In  one  we  can  trace  the  transformation.  We  know,  as  a  fact,  that 
heat  produces  expansion  (steam),  and  by  constructing  an  apparatus 
which  provides  for  the  application  of  the  expansive  power  in  opposite 
directions  alternately,  or  by  alternating  contraction  with  expansion,  we 
are  able  to  produce  motion  so  as  to  subserve  an  infinite  variety  of  pur- 
poses. For  the  continuance  of  the  motion  there  must  be  a  constant  sup- 
ply of  heat,  and  therefore  of  fuel. 

In  the  production  of  mechanical  motion  by  the  alternate  contractions 
of  muscular  fibres  we  cannot  trace  the  transformation  of  force  at  all. 
We  know  that  the  constant  supply  of  force  is  as  necessary  in  this 
instance  as  in  the  other;  and  that  the  food  which  an  animal  absorbs  is 
as  necessary  as  the  fuel  in  the  former  case,  and  is  analogous  with  it  in 
function.  In  what  exact  relation,  however,  the  latent  force  in  the  food 
stands  to  the  movement  in  the  fibre,  we  are  at  present  quite  ignorant. 
That  in  some  way  or  other,  however,  the  transformation  occurs,  we  may 
feel  quite  certain. 

There  is  another  distinction  between  the  two  exhibitions  of  force 
which  must  be  noticed.  It  has  been  universally  believed,  almost  up 
to  the  present  time,  that  in  the  production  of  living  force  the  result  is 
obtained  by  an  exactly  corresponding  waste  of  the  tissue  which  produces 
it;  that,  for  instance,  the  power  of  each  contraction  of  a  muscle  is  the 
exact   equivalent  of  the  force  produced  by  the  more  or  less  complete 


THE    RELATION    <>F    LIFE    TO    OTHER    FORCES.  7'2~ 

descent  of  so  much  muscular  substance  to  inorganic  or  less  complex 
organic  shape;  in  other  words, — that  the  immediate  fuel  which  an  animal 
requires  for  the  production  of  force  is  derived  from  its  own  substance; 
and  that  the  food  taken  must  first  be  appropriated  by,  and  enter  into 
the  very  formation  of  living  tissue  before  its  latent  force  can  be  trans- 
formed and  manifested  as  vital  power.  And  here,  it  might  be  said,  is  a 
great  distinction  between  a  living  structure  and  a  simply  mechanical 
arrangement  such  as  that  which  has  been  used  for  comparison;  the  fuel 
which  is  analogous  to  the  food  of  a  plant  or  animal  does  not,  as  in  the 
case  of  the  latter,  first  form  part  of  the  machine  which  transforms  its 
latent  energy  into  another  variety  of  power. 

We  are  not,  at  present,  in  a  position  to  deny  that  this  is  a  real  and 
great  distinction  between  the  two  cases;  but  modern  investigations  in 
more  than  one  direction  lead  to  the  belief  that  we  must  hesitate  before 
allowing  such  a  difference  to  be  an  universal  or  essential  one.  The 
experiments  referred  to  seem  conclusive  in  regard  to  the  production  of 
muscular  power  in  greater  amount  than  can  be  accounted  for  by  the 
products  of  muscular  waste  excreted;  and  it  may  be  said  with  justice 
that  there  is  no  intrinsic  improbability  in  the  supposed  occurrence  of 
transformation  of  force,  apart  from  equivalent  nutrition  and  subsequent 
destruction  of  the  transforming  agent.  Argument  from  analogy,  in- 
deed, would  be  in  favor  of  the  more  recent  theory  as  the  likelier  of  the 
two. 

"Whatever  may  be  the  result  of  investigations  concerning  the  relation 
of  waste  of  living  tissue  to  the  production  of  power,  there  can  be  no 
doubt,  of  course,  that  the  changes  in  any  part  which  is  the  seat  of  vital 
action  must  be  considerable,  not  only  from  what  may  be  called  "  wear 
and  tear,"  but,  also,  on  account  of  the  great  instability  of  all  organized 
structures.  Between  such  waste  as  this,  however,  and  that  of  an  inor- 
ganic machine  there  is  only  the  difference  in  degree,  arising  necessarily 
from  diversity  of  structure,  of  elementary  arrangement,  and  so  forth. 
But  the  repair  in  the  two  cases  is  different.  The  capability  of  recon- 
struction in  a  living  body  is  an  inherent  quality  like  that  which  causes 
growth  in  a  special  shape  or  to  a  certain  degree.  At  present  we  know 
nothing  really  of  its  nature,  and  we  are  therefore  compelled  to  express 
the  fact  of  its  existence  by  such  terms  as  "  inherent  power,"  "  individ- 
ual endowment/'  and  the  like,  and  wait  for  more  facts  which  may  ulti- 
mately explain  it.  Tins  special  quality  is  not  indeed  one  of  living  things 
alone.  The  repair  of  a  crystal  in  definite  shape  is  equally  an  "individ- 
ual endowment/'  or  "  inherent  peculiarity,"  of  the  nature  of  which  we 
are  equally  ignorant.  In  the  case,  however,  of  an  inorganic  machine 
there  is  nothing  of  the  sort,  not  even  as  in  a  crystal.  Faults  of  structure 
must  be  repaired  by  some  means  entirely  from  without.  Aud  as  our 
notion  of  a  living  being,  say  a  horse,  would  be  entirely  altered  if  flaws 


72S  HANDBOOK   OF   PHYSIOLOGY. 

in  his  composition  were  repaired  by  external  means  only;  so,  in  like 
manner,  would  our  idea  of  the  nature  of  a  steam-engine  be  completely 
changed  had  it  the  power  of  absorbing  and  using  part  of  its  fuel  as  mat- 
ter wherewith  to  repair  any  ordinary  injury  it  might  sustain. 

It  is  this  ignorance  of  the  nature  of  such  an  act  as  reconstruction 
which  causes  it  to  be  said,  with  apparent  reason,  that  so  long  as  the 
term  "  vital  force  "  is  used,  so  long  do  we  beg  the  question  at  issue — 
What  is  the  nature  of  life  ?  A  little  consideration,  however,  will  show 
that  the  justice  of  this  criticism  depends  on  the  manner  in  which  the 
word  "vital"  is  used.  If  by  it  we  intend  to  express  an  idea  of  some- 
thing which  arises  in  a  totally  different  manner  from  other  forces — some- 
thing which,  we  know  not  how,  depends  on  a  special  innate  quality  of 
living  beings,  and  owns  no  dependence  on  ordinary  physical  force,  but  is 
simply  stimulated  by  it,  and  has  no  correlation  with  it — then,  indeed,  it 
would  be  just  to  say  that  the  whole  matter  is  merely  shelved  if  we  retain 
the  term  "vital  force." 

But  if  a  distinct  correlation  be  recognized  between  ordinary  physical 
force  and  that  which  in  various  shapes  is  manifested  by  living  beings;  if 
it  be  granted  that  every  act — say,  for  example,  of  a  brain  or  muscle — is 
the  exactly  correlated  expression  of  a  certain  quantity  of  force  latent  in 
the  food  with  which  an  animal  is  nourished;  and  that  the  force  pro- 
duced either  in  the  shape  of  thought  or  movement  is  but  the  transformed 
expression  of  external  force,  and  can  no  more  originate  in  a  living  organ 
without  supplies  of  force  from  without,  than  can  that  organ  itself  be 
formed  or  nourished  without  supplies  of  matter; — if  these  facts  be  recog- 
nized, then  the  term  used  in  speaking  of  the  powers  exercised  by  a  liv- 
ing being  is  not  of  very  much  consequence.  We  have  as  much  right  to 
use  the  term  e<  vital  "  as  the  words  galvanic  and  chemical.  All  alike  are 
but  the  expressions  of  our  ignorance  concerning  the  nature  of  that  power 
of  which  all  that  we  call  "  forces  "  are  various  manifestations.  The  dif- 
ference is  in  the  apparatus  by  which  the  force  is  transformed. 

It  is  with  this  meaning  that,  for  the  present,  the  term  "  vital  force  " 
may  still  be  retained  when  we  wish  shortly  to  name  that  combination  of 
energies  which  we  call  life.  For,  exult  as  we  may  at  the  discovery  of 
the  transformation  of  physical  force  into  vital  action,  we  must  acknowl- 
edge not  only  that,  with  the  exception  of  some  slight  details,  we  are 
utterly  ignorant  of  the  process  by  which  the  transformation  is  effected; 
but,  as  well,  that  the  result  is  in  many  ways  altogether  different  from 
that  of  any  other  force  with  which  we  are  acquainted. 

It  is  impossible  to  define  in  what  respects,  exactly,  vital  force  differs 
from  any  other.  For  while  some  of  its  manifestations  are  identical  with 
ordinary  physical  force,  others  have  no  parallel  whatsoever.  And  it  is 
this  mixed  nature  which  has  hitherto  baffled  all  attempts  to  define  life, 
and,  likeaWill-o'-the-wisp,  hasledusflounderingon  through  onedefinition 


THE    RELATION    OF    LIFE   TO    OTHER    FORCES.  729 

after  another  only  to  escape  our  grasp  and  show  our  impotence  to 
seize  it. 

In  examining,  therefore,  the  distinctions  between  the  products  of 
transformations  by  a  living  and  by  an  inorganic  machine,  Ave  have 
first  to  recognize  the  fact,  that  while  in  some  cases  the  difference  is  so 
faint  as  to  be  nearly  or  quite  imperceptible,  in  others  there  seems  not  a 
trace  of  resemblance  to  be  discovered. 

In  discussing  the  nature  of  life's  manifestations — birth,  growth,  de- 
velopment, and  decline — the  differences  which  exist  between  them  and 
other  processes  more  or  less  resembling  them,  but  not  dependent  on  life, 
have  been  already  briefly  considered  and  need  not  be  here  repeated.  It 
may  be  well,  however,  to  sum  up  very  shortly  the  particulars  in  which 
life  as  a  manifestation  of  force  differs  from  all  others. 

The  mere  acquirement  of  a  certain  shape  by  growth  is  not  a  pecu- 
liarity of  life.  But  the  power  of  developing  into  so  composite  a  mass 
even  as  a  vegetable  cell  is  a  property  possessed  by  an  organized  being 
only.  In  the  increase  of  inorganic  matter  there  is  no  development. 
The  minutest  crystal  of  any  given  salt  has  exactly  the  same  shape  and 
intimate  structure  as  the  largest.  With  the  growth  there  is  no  develop- 
ment. There  is  increase  of  size  with  retention  of  the  original  shape, 
but  nothing  more.  And  if  we  consider  the  matter  a  little  we  shall  see  a 
reason  for  this.  In  all  force-transformers,  whether  living  or  inorganic, 
with  but  few  exceptions — and  these  are,  probably,  apparent  only — some- 
thing more  is  required  than  homogeneity  of  structure.  There  seems  to 
be  a  need  for  some  mutual  dependence  of  one  part  on  another,  some  dis- 
tinction of  qualities,  which  cannot  happen  when  all  portions  are  exactly 
alike.  And  here  lies  the  resemblance  between  a  living  being  and  an  arti- 
ficial machine.  Both  are  developments,  and  depend  for  their  power  of 
transforming  force  on  that  mutual  relation  of  the  several  jjarts  of  their 
structure  which  we  call  organization.  But  here,  also,  lies  a  great  dif- 
ference. The  development  of  a  living  being  is  due  to  an  inherent 
tendency  to  assume  a  certain  form;  about  which  tendency  we  know 
absolutely  nothing.  We  recognize  the  fact,  and  that  is  all.  The  de- 
velopment of  an  inorganic  machine — say  an  electrical  apparatus — is  not 
due  to  an  inherent  or  individual  property.  It  is  the  result  of  a  power 
entirely  from  without;  and  we  know  exactly  how  to  construct  it. 

Here,  then,  again,  we  recognize  the  compound  nature  of  a  living 
being.  In  structure  it  is  altogether  different  from  a  crystal— in  inhe- 
rent capacity  of  growth  into  definite  shape  it  resembles  it.  Again,  in 
the  fact  of  its  organization  it  resembles  a  machine  made  by  man:  in  ca- 
pacity of  growth  it  entirely  differs  from  it.  In  regard,  therefore,  to 
structure,  growth,  and  development,  it  has  combined  in  itself  qualities 
which  in  all  other  things  are  more  or  less  completely  separated. 

That  modification  of  ordinary  growth  and  development  called  gen- 


730  HANDBOOK    OF    PHYSIOLOGY. 

eration,  which  consists  in  the  natural  production  and  separation  of  a 
portion  of  organized  structure,  with  power  itself  to  transform  force  so  as 
therewith  to  build  up  an  organism  like  the  being  from  which  it  was 
thrown  off,  is  another  distinctive  peculiarity  of  a  living  being.  We 
know  of  nothing  like  it  in  the  organic  world.  And  the  distinction  is 
the  greater  because  it  is  the  fulfilment  of  a  purpose,  towards  which  life 
is  evidently,  from  its  very  "beginning,  constantly  tending.  It  is  "as 
natural  a  destiny  to  separate  parts  which  shall  form  independent  beings 
as  it  is  to  develop  a  limb.  Hence  it  is  another  instance  of  that  carrying 
out  of  certain  projects,  from  the  very  beginning  in  view,  which  is  so 
characteristic  of  things  living  and  of  no  other. 

It  is  especially  in  the  discharge  of  what  are  called  the  animal  func- 
tions that  we  see  vital  force  most  strangely  manifested.  It  is  true  that 
one  of  the  actions  included  in  this  term — namely  mechanical  movement 
— although  one  of  the  most  striking,  is  by  no  means  a  distinctive  one. 
For  it  must  be  remembered  that  one  of  the  commonest  transformations 
of  physical  force  with  which  we  are  acquainted  is  that  of  heat  into  me- 
chanical motion,  and  that  this  may  be  effected  by  an  apparatus  having 
itself  nothing  whatever  to  do  with  life.  The  peculiarity  of  the  mani- 
festation in  an  animal  or  vegetable  is  that  of  the  organ  by  which  it  is 
effected,  and  the  manner  in  which  the  transformation  takes  place,  not 
in  the  ultimate  result.  The  mere  fact  of  an  animal's  possessing  capa- 
bility of  movement  is  not  more  wonderful  than  the  possession  of  a  simi- 
lar property  by  a  steam  engine.  In  both  cases  alike,  the  motion  is  the 
correlative  expression  of  force  latent  in  the  food  and  fuel  respectively; 
but  in  one  case  we  can  trace  the  transformation  in  the  arrangement  of 
parts,  in  the  other  we  cannot. 

The  consideration  of  the  products  of  the  transformation  of  force 
effected  by  the  nervous  system  would  lead  far  beyond  the  limits  of  the 
present  chapter.  But  although  the  relation  of  mind  to  matter  is  so 
little  known  that  it  is  impossible  to  speak  with  any  freedom  concerning 
such  correlative  expressions  of  physical  force  as  thought  and  nerve-pro- 
ducts, still  it  cannot  be  doubted  that  they  are  as  much  the  results  of 
transformation  of  force  as  the  mechanical  motion  caused  by  the  con- 
traction of  a  muscle.  But  here  the  mystery  reaches  its  climax.  We 
neither  know  how  the  change  is  effected,  nor  the  nature  of  the  product, 
nor  its  analogies  with  other  forces.  It  is  therefore  better,  for  the  pres- 
ent, to  confess  our  ignorance,  than,  with  the  knowledge  which  we  have 
lately  gained  to  build  up  rash  theories,  serving  only  to  cause  that  con- 
fusion which  is  worse  than  error. 

It  may  be  said,  with  perfect  justice,  that  even  if  the  foregoing  con- 
clusions be  accepted,  namely,  that  all  manifestations  of  force  by  living 
beings  are  correlative  expressions  of  ordinary  physical  force,  still  the 
argument  is  based  on  the  assumption  of  the  existence  of  the  apparatus 


THE    RELATION    OF    LIFE    TO    OTHER    FORCES.  7ol 

which  we  call  living  organized  matter,  with  power  not  only  to  use  ex- 
ternal force  for  its  own  use  in  growth,  development,  and  other  vital  mani- 
festations, but  for  that  modification  of  these  powers  which  consists  in  the 
separation  of  a  part  that  shall  grow  up  into  the  likeness  of  its  parent, 
and  thus  continue  the  race.  We  are  therefore,  it  may  be  added,  as  far 
as  ever  from  any  explanation  of  the  origin  of  life.  This  is  of  course 
quite  true.  The  object  of  the  present  chapter,  however,  is  only  to  deal 
with  the  relations  of  life,  as  it  now  exists,  to  other  forces.  The  manner 
of  creation  of  the  various  kinds  of  organized  matter,  and  the  source  of 
those  qualities,  belonging  to  it,  which  from  our  ignorance  we  call  in- 
herent, are  different  questions  altogether. 

To  say  that  of  necessity  the  power  to  form  living  organized  matter  will 
never  be  vouchsafed  to  us,  that  it  is  only  a  mere  materialist  who  would 
believe  in  such  a  possibility,  seems  almost  as  absurd  as  the  statement 
that  such  inquiries  lead  of  necessity  to  the  denial  of  any  higher  power 
than  that  which  in  various  forms  is  manifested  as  "  force, '"'  on  this  small 
portion  of  the  universe.  It  is  almost  as  absurd,  but  not  quite.  For, 
surely,  he  who  recognizes  the  doctrine  of  the  mutual  convertibility  of 
all  forces,  vital  and  physical,  who  believes  in  their  unity  and  imperish- 
ableness,  should  be  the  last  to  doubt  the  existence  of  an  all-powerful 
Being,  of  whose  will  they  are  but  the  various  correlative  expressions 
from  whom  they  all  come;  to  whom  they  return. 


APPENDIX. 


The  Chemical  Basis  of  the  Human  Body. 

Of  the  sixty-seven  known  chemical  elements  no  less  than  seventeen 
combine,  in  large  or  smaller  quantities,  to  form  the  chemical  basis  of 
the  animal  body. 

The  substances  which  contribute  the  largest  share  are  the  non-metal- 
lic elements,  Oxygen,  Carbon,  Hydrogen,  and  Nitrogen— oxygen 
and  carbon  making  up  altogether  about  85  per  cent  of  the  whole.  The 
most  abundant  of  the  metallic  elements  are  Calcium,  Sodium,  and 
Potassium. 

The  following  table  represents  the  relative  proportion  of  the  various 
elements. — (Marshall. ) 


Oxygen,      . 

72.0 

Fluorine,           .         .         .         .08 

Carbon,  . 

.  13  5 

Potassium,         .        .           .026 

Hydrogen, . 

9.1 

Iron, 01 

Nitrogen, 

.     2.5 

Magnesium,           .         .             .0012 

Calcium, 

1.3 

Silicon, 0002 

Phosphorus,     . 

.     1.15 

(Traces  of  copper,  lead,  and 

Sulphur, 

.1476 

aluminium), 

Sodium, 

.1 

Chlorine,     . 

.'o85 

100. 

Compounds. — Few  of  these  elementary  substances  occur  free  or  un- 
combined  in  the  animal  body.  They  are  generally  united  in  various 
numbers,  and  in  variable  proportions  to  form  compounds.  Traces  of 
uncombined  Oxygen  and  Nitrogen,  however,  have  been  found  in  the 
blood,  and  of  Hydrogen  as  well  as  of  Oxygen  and  Nitrogen  in  the  intes- 
tinal canal. 

It  was  formerly  thought  that  the  more  complex  compounds  built  up 
by  the  animal  or  vegetable  organism  were  peculiar,  and  could  not  be 
made  artificially  by  chemists  from  their  elements,  and  under  this  idea 
they  were  formed  into  a  distinct  class,  termed  organic.  This  idea  has 
been  given  up,  but  the  name  is  still  in  use,  with  a  different  signification. 
The  term  is  now  applied  simply  to  the  compounds  of  the  element  Car- 
bon, irrespective  of  their  origin. 

Characteristics  of  Organic  Compounds. — A  large  number  of  the  ani- 
mal organic  compounds  are  characterized  by  their  complexity.     Many 


APPENDIX.  733 

elements  may  enter  into  their  composition,  thereby  distinguish ing  them 
from  bodies  as  simple  as  water  (H40),  hydrochloric  acid  (HC1),  and  am- 
monia (N  Hs),  which  may  be  taken  as  types  of  inorganic  compounds. 
Many  atoms  of  the  same  eiement  also  may  occur  in  each  molecule.  This 
latter  fact  no  doubt  explains  also  the  reason  of  the  instability  of  these 
compounds.  Another  great  cause  of  the  instability  is  the  frequent 
presence  of  Nitrogen,  which  may  be  called  negative  or  undecided  in  its 
affinities,  and  may  be  easily  separated  from  combination  with  other 
elements. 

Animal  tissues,  containing  as  they  do  these  organic  nitrogenous  com- 
pounds, are  extremely  prone  to  undergo  chemical  decomposition.  They 
also  contain  a  large  quantity  of  water,  a  condition  most  favorable  for  the 
breaking  up  of  such  substances.  It  is  due  to  this  tendency  to  decompo- 
sition that  we  meet  with  so  large  a  number  of  decomposition  products 
among  the  chemical  substances  forming  the  basis  of  the  animal  body. 

The  various  substances  found  in  the  animal  organism  may  be  conve- 
niently considered  according  to  the  following  classification: — 

..     n       •      j  a.   Nitrogenous. 

1.  ugamc,    ^   Non-Nitrogenous. 

2.  Inorganic. 

1.  Organic. 

(a.)  Nitrogenous  bodies  take  the  chief  part  in  forming  the  solid  tis- 
sues of  the  body,  and  are  found  also  to  a  considerable  extent  in  the  cir- 
culating fluids  (blood,  lymph,  chyle),  the  secretions  and  excretions. 
They  often  contain  in  addition  to  Carbon,  Hydrogen,  Nitrogen,  and 
Oxygen,  the  elements  Sulphur  and  Phosphorus  ;  but  although  the  com- 
position of  most  of  them  is  approximately  known,  no  general  rational 
formula  can  at  present  be  given. 

Several  classes  of  organic  nitrogenous  bodies  may  be  distinguished, 
and  it  is  convenient  to  consider  them  under  the  following  heads: — 

(1.)  Proteids  or  albuminoids. 

(2.)  Gelatinous  substances. 

(3.)  Decomposition  nitrogenous  bodies. 

(4.)  Certain  nitrogenous  bodies,  the  exact  composition  of  which  has 
not  been  made  out. 

(1.)  Proteids  or  Albuminoids  are  the  most  important  of  the  nitro- 
genous animal  compounds,  one  or  more  of  them  entering  as  essential 
parts  into  the  formation  of  all  living  tissue.  In  the  lymph,  chyle,  and 
blood,  they  also  exist  abundantly.  Their  atomic  formula  is  uncertain. 
Their  composition,  according  to  Hoppe-Seyler,  may  be  taken  to  be: — 

Carbon,  from  51.5  to  54.5;  Hydrogen,  from  6.9  to  7.3;  Nitrogen, 
from  15.2  to  17.;  Oxygen,  from  20.9  to  23.5;  Sulphur,  from  .3  to  2. 


734  APPENDIX. 

• 

Physical  Properties. — Proteicis  are  all  amorphous  and  non-crystalliz- 
able,  so  that  they  possess  as  a  rale  no  power  (or  scarcely  any)  of  passing 
through  animal  membranes.  They  are  soluble,  but  undergo  alteration 
in  composition  in  strong  acids  and  alkalies  ;  some  are  soluble  in  water, 
others  in  neutral  saline  solutions,  some  in  dilute  acids  and  alkalies,  few 
in  alcohol  or  ether.  Their  solutions  exercise  a  left-handed  action  on 
polarized  light. 

Chemical  Properties. — Certain  general  reactions  are  given  for  pro- 
teids.    They  are  a  little  varied  in  each  particular  case: — 

i.  Xantho-Proteic  Reaction. — A  solution  boiled  with  strong 
nitric  acid,  becomes  yellow,  and  the  color  is  darkened  on  addi- 
tion of  ammonia. 

ii.  Biuret  Reaction. — With  a  trace  of  copper  sulphate  and  an 
excess  of  potassium  or  sodium  hydrate  they  give  a  purple  col- 
oration. 

iii.  Millon's  Reaction. — With  Millon's  reagent  (a  solution  of  me- 
tallic mercury  in  strong  nitric  acid),  they  give  a  white  or  pink- 
ish clotted  precipitate,  becoming  more  pink  on  boiling. 

iv.  They  are,  with  the  exception  of  peptone,  entirely  precipitated 
from  their  solutions  by  saturation  with  ammonium  sulphate. 

Many  of  the  proteids  give,  in  addition,  the  following  tests: 

v.  With  excess  of  acetic  acid,  and  potassium  ferro-cyanide,  a  white 

precipitate, 
vi.  With  excess  of  acetic  acid  and  a  saturated  solution  of  sodium 
sulphate,  on  boiling,  a  white  precipitate.     This  test  is  often 
used  to  get  rid  of  all  traces  of  proteids,  except  peptones,  from 
solutions, 
vii.  Boiled  with  strong  hydrochloric  acid,  they  give  a  violet  red 

coloration, 
viii.  With  cane  sugar  and  strong  sulphuric  acid,  on  heating,  they 

give  a  purplish  coloration, 
ix.    They  are  precipitated  on  addition  of — 

Citric  or  acetic  acid,  and  picric  acid  ;  or, 
Citric  or  acetic  acid,  and  sodium  tungstate  ;  or 
Citric  or  acetic  acid,  and  potassio-mecuric  iodide. 

Varieties. — Proteids  are  divided  into  seven  classes,  chiefly  on  the 
basis  of  their  solubilities  in  various  reagents.  Each  class,  however,  if 
it  contains  more  than  one  substance,  may  often  be  distinguished  by 
other  properties  common  to  its  members. 

(1.)  Native- Albumins. — These  substances  are  soluble  in  water  and 
in  saline  solutions,  and  are  coagulated,  i.  e.,  turned  into  coagulated  pro- 
teid,  on  heating. 

(2.)  Derived- Albumins. — These  are  soluble  in  acids  or  alkalies,  but 
insoluble  in  saline  solutions  and  in  water,  and  are  not  coagulated  on 
heating. 

(3.)  Globulins. — These  are  soluble  in  strong  or  in  weak  saline  solu- 
tions, in  dilute  acids  and  alkalies,  and  insoluble  in  water.  They  are  co- 
agulated on  heating. 


APPENDIX.  735 

(4.)  Fibrin. — It  is  insoluble  in  water,  in  dilute  saline  solutions,  or 
in  dilute  acids  or  alkalies;  soluble  in  strong  saline  solutions  (partly)  and 
in  strong  acids;  soluble  to  a  certain  extent  in  strong  saline  solutions  and 
in  gastric  or  pancreatic  fluids. 

(5.)  Peptones. — These  are  soluble  in  water,  saline  solutions,  acids, 
or  alkalies  ;  they  are  not  coagulated  on  heating. 

(6.)  Coagulated  Proteids. — These  are  soluble  only  in  gastric  or  pan- 
creatic fluids,  forming  peptones. 

(7.)  Amyloid  substance,  or  Lardacein. — This  body  is  generally  insol- 
uble, even  in  gastric  or  pancreatic  fluids  at  ordinary  temperatures.  It 
gives  a  brown  coloration  with  iodine. 

Class  I. — Native- Albumins. 

(a)  Egg- Albumin  is  contaiued  in  the  white  of  the  egg. 
Properties. — When  in  solution  in  water  it  is  a  transparent,  frothy, 

yellowish  fluid,  neutral  or  slightly  alkaline  in  reaction. 

It  gives  all  of  the  general  proteid  reactions. 

At  a  temperature  not  exceeding  40°  C.  it  is  dried  up  into  a  yellowish 
transparent,  glassy  mass,  soluble  in  water. 

At  a  temperature  of  70°  C.  it  is  coagulated,  i.  e.,  changed  into  anew 
substance,  coagulated  proteid,  which  is  quite  insoluble  in  water.  It  is 
coagulated  also  by  the  prolonged  action  of  alcohol ;  by  strong  mineral 
acids,  especially  by  nitric  acid,  also  by  tannic  acid,  or  carbolic  acid  ;  by 
ether  the  coagulum  is  soluble  in  caustic  soda. 

It  is  precipitated  without  coagulation,  i.  e.,  forms  an  insoluble  com- 
pound with  the  reagent,  soluble  on  removal  of  the  salt  by  dialysis,  with 
either  mercuric  chloride,  lead  acetate,  copper  sulphate  or  silver  nitrate, 
the  precipitate  being  soluble  in  slight  excess  of  the  reagent. 

With  strong  nitric  acid  the  albumin  is  precipitated  at  the  point  of 
contact  with  the  acid  in  the  form  of  a  fine  white  or  yellow  ring. 

(b)  Serum- Albumin  is  contained  in  blood  serum,  lymph,  serous, 
and  synovial  fluids,  and  the  tissues  generally  ;  it  appears  in  the  urine  in 
the  condition  known  as  albuminuria.  Two  varieties,  metalbumin  and 
paralbumin,  have  been  described  as  existing  in  dropsical  fluids  and  ova- 
rian cysts  respectively. 

It  gives  similar  reactions  to  egg-albumin,  but  differs  from  it  in  not 
being  coagulated  by  ether.  It  also  differs  from  egg-albumin  in  not  be- 
ing easily  precipitated  by  hydrochloric  acid,  and  in  the  precipitate  being 
easily  soluble  in  excess  of  that  acid.  Serum-albumin,  either  in  the  co- 
agulated or  precipitated  form,  is  more  soluble  in  excess  of  strong  acid 
than  egg-albumin. 

The  compound  nature  of  what  is  usually  called  serum-albumin,  or 
serine,  and  its  differentiation  into  three  substances,  coagulate  at  differ- 


736  APPENDIX. 

ent  temperatures,  viz.,  a.  at  73°  (J.,  /?.  at  77°  C,  and  y.  at  85°  C,  as- 
demonstrated  by  Halliburton,  as  well  as  its  other  properties,  are  men- 
tioned at  p.  79. 

Class  II. — Derived-Albumins. 

(a)  Acid-Albumin. — Acid-albumin  is  made  by  adding  small  quanti- 
ties of  dilute  acid  (of  which  the  best  is  hydrochloric,  .4  per  cent  to  1  per 
cent),  to  either  egg-  or  serum-albumin  diluted  with  five  to  ten  times  its 
bulk  of  water,  and  keeping  the  solution  at  a  temperature  not  higher  than 
50°  C.  for  not  less  than  half  an  hour. 

It  may  also  be  made  by  dissolving  coagulated  native-albumin  in 
strong  acid,  or  by  dissolving  any  of  the  globulins  in  acids. 

It  is  not  coagulated  on  heating,  but  on  exactly  neutralizing  the  solu- 
tion, a  flocculent  precipitate  is  produced.  This  may  be  shown  by  ad- 
ding to  the  acid-albumin  solution  a  little  aqueous  solution  of  litmus, 
and  then  adding,  drop  by  drop,  a  weak  solution  of  caustic  potash  from 
a  burette,  until  the  red  color  disappears.  The  precipitate  is  the  derived 
albumin.  It  is  soluble  in  dilute  acid,  dilute  alkalies,  and  dilute  solutions 
of  alkaline  carbonates. 

The  solution  of  acid-albumin  gives  the  proteid  tests.  The  substance 
itself  is  coagulated  by  strong  acids,  e.  g.,  nitric  acid,  and  by  strong  alco- 
hol; it  is  insoluble  in  distilled  water,  and  in  neutral  saline  solutions;  it  is 
precipitated  from  its  solutions  by  saturation  with  sodium  chloride.  On 
boiling  in  lime-water  it  is  partially  coagulated,  and  a  further  precipita- 
tion takes  place  on  addition  to  the  boiled  solution  of  calcium  chloride,, 
magnesium  sulphate,  or  sodium  chloride. 

(b)  Alkali-Albumin. — If  solutions  of  native-albumin,  or  coagulated 
or  other  proteid,  be  treated  with  dilute  or  strong  fixed  alkali,  alkali-albu- 
min is  produced.  Solid  alkali-albumin  may  also  be  prepared  by  adding 
caustic  soda  or  potash,  drop  by  drop,  to  undiluted  egg-albumin,  until 
the  whole  forms  a  jelly.  This  jelly  is  soluble  in  dilute  alkalies  on  boil- 
ing. 

A  solution  of  alkali-albumin  gives  the  tests  corresponding  to  those 
of  acid-albumin.  It  is  not  coagulated  on  heating.  It  is  thrown  down 
on  neutralizing  its  solution,  except  in  the  presence  of  alkaline  phos- 
phates, in  which  case  the  solution  must  be  distinctly  acid  before  a  pre- 
cipitate falls. 

To  differentiate  between  Acid-  and  Alkali- Albumin,  the  following 
method  may  be  adopted.  Alkali-albumin  is  not  precipitated  on  exact  neu- 
tralization, if  sodium  phosphate  has  been  previously  added.  Acid-albu- 
min is  precipitated  on  exact  neutralization,  whether  or  not  sodium  phos- 
phate has  been  previously  added. 

(c)  Casein. — Casein  is  the  chief  proteid  of  milk,  from  which  it 
may  be  prepared  by  the  following  process:  The  milk  should  be  diluted 


APPENDIX.  737 

with  three  to  four  times  its  volume  of  water,  sufficient  dilute  acetic  acid 
should  then  be  added  to  render  the  solution  distinctly  acid,  and  the 
casein  which  is  thrown  down  may  be  separated  by  filtration.  It  may 
then  be  washed  with  alcohol  and  afterwards  with  ether,  to  free  it  from 
fat. 

Casein  may  also  be  prepared  by  adding  to  milk  an  excess  of  crystallized 
magnesium  sulphate  or  sodium  chloride,  either  of  which  salt  causes  it  to 
separate  out. 

Casein  gives  much  the  same  tests  as  alkali-albumin.  It  is  soluble  in 
dilute  acid  or  alkalies;  it  isreprecipitated  on  neutralization,  but  if  potas- 
sium phosphate  be  present  the  solution  must  be  distinctly  acid  before 
the  casein  is  deposited. 

Class  III. — Globulins. 

General  Properties  of  Globulins. — They  give  the  general  proteid 
tests;  are  insoluble  in  water;  are  soluble  in  dilute  saline  solutions; 
are  soluble  in  acids  and  alkalies  forming  the  corresponding  derived- 
albumin. 

Most  of  them  are  precipitated  from  their  solutions  by  saturation 
with  solid  sodium  chloride,  magnesium  sulphate,  and  other  neutral 
salts. 

They  are  coagulated,  but  at  different  temperatures,  on  heating. 

(a)  Globulin  or  Crystallin. — It  is  obtained  from  the  crystalline 
lens  by  rubbing  it  up  with  powdered  glass,  extracting  with  water  or  with 
dilute  saline  solution,  and  by  passing  through  the  extract  a  stream  of  car- 
bon dioxide. 

It  differs  from  other  globulins,  except  vitellin,  in  not  being  precipi- 
tated by  saturation  with  sodium  chloride. 

(b)  Myosin. — Myosin  may  be  prepared,  as  was  before  described, 
from  dead  muscle,  by  removing  all  fat,  tendon,  etc.,  and  washing  re- 
peatedly in  water,  until  the  washing  contains  no  trace  of  proteids, 
mincing  it,  and  then  treating  with  10  per  cent  solution  of  sodium  chlo- 
ride, or  similar  solution  of  ammonium  chloride,  magnesium  sulphate, 
which  will  dissolve  a  large  portion  into  a  viscid  fluid,  which  filters  with 
difficulty.  If  the  viscid  filtrate  be  dropped  little  by  little  into  a  large 
quantity  of  distilled  water,  a  white  flocculent  precipitate  of  myosin  will 
occur. 

It  is  soluble  in  10  per  cent  saline  solution;  it  is  coagulated  at  60°  C 
into  coagulated  proteid;  it  is  soluble  without  change  in  very  dilute 
acids;  it  is  precipitated  by  picric  acid,  the  precipitate  being  redissolved 
on  boiling;  it  may  give  a  blue  color  with  ozonic  ether  and  tincture  of 
guaiacum.  The  formation  of  a  clot  of  myosin  on  dilution  of  the  strong 
saline  solution  in  which  it  is  contained,  has  been  already  commented 
upon. 

47 


738  APPENDIX. 

(c)  Paraglobulin. — Paraglobulin  is  contained  in  serum  and  in 
serous  and  synovial  fluids,  and  may  be  precipitated  by  saturating  serum 
with  solid  sodium  chloride  or  magnesium  sulphate,  as  a  bulky  flocculent 
substance,  which  can  be  removed  by  filtration  after  standing  for  some 
time. 

It  may  also  be  prepared  by  diluting  blood  serum  with  ten  volumes  of 
water,  and  passing  carbonic  acid  gas  rapidly  through  it.     The  fine  pre 
cipitate  may  be  collected  on  filter,  and  washed  with  water  containing 
carbonic  acid  gas. 

It  is  very  soluble  in  dilute  saline  solutions,  from  which  it  is  precipi- 
tated by  carbonic  acid  gas  or  by  dilute  acids;  its  solution  is  coagulated 
at  70°  C.  ;  even  dilute  acids  and  alkalies  convert  it  into  acid-  or  alkali- 
albumin. 

(d)  Fibrinogen. — Fibrinogen  is  prepared  from  hydrocele  fluid  or 
other  serous  transudation  by  methods  similar  to  those  employed  in  pre- 
paring paraglobulin  from  serum. 

Its  general  reactions  are  similar  to  those  of  paraglobulin;  its  solution 
is  coagulated  at  52°-55°  C.  Its  characteristic  property  is  that,  under 
certain  conditions,  it  forms  fibrin. 

(e)  Vitellin. — Vitellin  is  prepared  from  yolk  of  egg  by  washing 
with  ether  until  all  the  yellow  matter  has  been  removed.  The  residue 
is  dissolved  in  10  per  cent  saline  solution,  filtered,  and  poured  into  a 
large  quantity  of  distilled  water.  The  precipitate  which  falls  is  impure 
vitellin. 

It  gives  the  same  tests  as  myosin,  but  is  not  precipitated  on  saturation 
with  sodium  chloride;  it  coagulates  between  70°  and  83°  C. 

(f)  Globin. — Is  the  proteid  residue  of  haBmoglobin. 

Class  IV. 

Fibrin. — Fibrin  can  be  obtained  as  a  soft,  white,  fibrous,  and  very 
elastic  substance  by  whipping  blood  with  a  bundle  of  twigs,  and  washing 
the  adhering  mass  in  a  stream  of  water  until  all  the  blood-coloring  mat- 
ter is  removed. 

Tests. — It  differs  from  all  other  proteids,  in  having  a  filamentous 
structure.  It  is  insoluble  in  water  and  in  dilute  saline  solutions;  slightly 
soluble  in  concentrated  saline  solutions,  soluble  on  boiling  in  strong  acids 
and  alkalies.  On  boiling  it  is  converted  into  coagulated  proteid.  When 
dissolved  in  strong  saline  solution  it  gives  many  of  the  same  reactions  as 
myosin.  When  dissolved  in  acids  or  alkalies,  it  is  converted  into  the 
corresponding  derived-albumin.  It  gives  a  blue  color  with  tincture  of 
guaiacum  and  ozonic  ether. 


APPENDIX.  739 

Class  V. 

Peptone. — Peptone  is  formed  by  the  action  of  the  digestive  ferments, 
pepsin,  or  trypsin,  on  other  proteids,  and  on  gelatin. 

The  properties  and  tests  for  peptone  are  at  present  very  unsatisfac- 
tory, owing  to  the  fact  that  the  substance  can  be  obtained  in  a  pure  con- 
dition with  extreme  difficulty.  Many  of  the  following  tests,  therefore, 
which  are  usually  given  for  the  substance,  are  very  likely  due  to  impuri- 
ties, intermediate  digestion  products,  or  albumose.  A  solution  of  com- 
mercial peptone  in  water  gives  the  following  tests: 

It  is  not  coagulated  on  heating;  it  is  not  precipitated  by  saturation 
with  NaCl,  or  MgS04,  or  by  COa.  It  is  not  precipitated  by  boiling  with 
sodium  sulphate  and  acetic  acid.  It  is  not  precipitated  by  addition  of 
dilute  acid  or  alkali.  It  is  precipitated  from  neutral  or  slightly  acid  solu- 
tions by: 

Mercuric  chloride,  the  precipitate  being  only  partly  soluble  in 
excess;  argentic  nitrate;  lead  acetate;  potassio-mercuric  iodide; 
bile  salts;  phosphoro-molybdic  acid;  tannin,  the  precipitate 
being  soluble  in  dilute  acid,  but  not  in  excess  of  the  reagent. 
Picric  acid  (saturated  solution),  the  precipitate  disappears  on 
heating,  and  partly  returns  on  cooling.  It  is  precipitated,  but 
not  coagulated  by  absolute  alcohol,  and  by  ether.  The  solution 
of  impure  peptone  gives 

The  Xanthoproteic  reaction  easily,  but  there  is  very  slight,  if  any 
previous  precipitation  with  the  nitric  acid. 

The  Biuret  reaction — but  the  color  is  pink  instead  of  violet. 

With  Millon's  test — not  so  easily  as  do  native  albumins. 

With  Ferrocyanide  and  acetic  acid — only  in  cases  where  the  pep- 
tone is  very  impure,  is  there  any  precipitate. 
The  only  substance  which  appears  to  separate  the  whole  of  the  other 
proteids  from  peptone  is  ammonium  sulphate. 
It  dialyzes  freely. 

Class  VI. 

Coagulated  proteids  are  formed  by  the  action  of  heat  upon  other 
proteids;  the  temperature  necessary  in  each  case  varying  in  the  manner 
previously  indicated.  They  may  also  be  produced  by  the  prolonged  ac- 
tion of  alcohol  upon  proteids. 

They  are  soluble  in  strong  acids  or  alkalies;  slightly  so  in  dilute;  are 
soluble  in  digestive  fluids  (gastric  and  pancreatic).  Are  insoluble  in  saline 
solutions. 

Class  VII. 

Lardacein  is  found  in  organs  which  are  the  seat  of  amyloid  degenera- 
tion. 


74:0  APPENDIX. 

It  is  insoluble  in  dilute  acids  and  in  gastric  juice  at  the  temperature 
of  the  body.  It  is  colored  brown  by  iodine  and  bluish-purple  by  methyl 
violet. 

(2.)  The  Gelatins  or  Nitrogenous  Bodies  other  than  Proteids. 

(a)  Gelatin. — Gelatin  is  contained  in  bone,  teeth,  fibrous  connective 
tissues,  tendons,  ligaments,  etc.  It  may  be  obtained  by  prolonged  action 
of  boiling  water  in  a  Papin's  digester,  or  of  dilute  acetic  acid  at  a  low 
temperature  (15°  C). 

Properties. — The  percentage  composition  is  0,  23.21,  H,  7.15,,  N, 
18.32,  C,  50.76,  S,  0.56.  It  contains  more  nitrogen  and  less  carbon  than 
proteids.  It  is  amorphous,  and  transparent  when  dried.  It  does  not 
dialyze;  it  is  insoluble  in  cold  water,  but  swells  up  to  about  six  times 
its  volume:  it  dissolves  readily  on  the  addition  of  very  dilute  acids  or 
alkalies.  It  is  soluble  in  hot  water,  and  forms  a  jelly  on  cooling,  even 
when  only  1  per  cent  of  gelatin  is  present.  Prolonged  boiling  in 
dilute  acids,  or  in  water  alone,  destroys  this  power  of  forming  a  jelly  on 
cooling. 

A  fairly  strong  solution  of  gelatin — 2  per  cent  to  4  per  cent — gives 
the  following  reactions: 

(a)  With  proteid  tests:  (i.)  Xanthoproteic  test. — A  yellow  color  with 
no  previous  precipitate  with  nitric  acid,  becoming  darker  on  the 
addition  of  ammonia,  (ii.)  Biuret  test. — A  violet  color,  (iii.) 
Milhn's  test. — A  pink  precipitate,  (iv.)  Potassium  ferrocyanide 
and  acetic  acid. — No  reaction,  (v.)  Boiling  with  sodium  sul- 
phate and  acetic  acid. — No  reaction. 

(b)  Special  reactions:  (i.)  No  precipitate  with  acetic  acid,  (ii.)  No 
precipitate  with  hydrochloric  acid,  (iii.)  A  white  precipitate 
with  tannic  acid,  not  soluble  in  excess  or  in  dilute  acetic  acid, 
(iv.)  A  white  precipitate  with  mercuric  chloride,  unaltered  by 
excess  of  the  reagent,  (v.)  A  white  precipitate  with  alcohol, 
(vi.)  A  yellowish-white  precipitate  with  picric  acid,  dissolved  on 
heating  and  reappearing  on  cooling. 

Bone  consists  of  an  organized  matrix  of  connective  tissue  which  yields 
gelatin  and  inorganic  salts. 

Inorganic  salts  can  be  removed  by  digesting  it  in  hydrochloric  acid. 
The  gelatinous  matter  left  retains  the  form  of  the  bone.  By  long  boiling 
in  water  it  is  converted  into  a  solution  of  a  gelatin. 

When  bone  is  heated,  the  first  action  is  to  decompose  the  organic 
matter,  leaving  a  deposit  of  carbon.  On  further  ignition  in  air  this  car- 
bon burns  away,  and  only  inorganic  salts  (principally  calcic  phosphate) 
are  left. 

(b)  Mucin. — Mucin  is  the  characteristic  component  of  mucus;  it  is 
contained  in  foetal  connective  tissue,  tendons,  and  salivary  glands.     It 


APPENDIX.  741 

may  be  prepared  from  ox-gall,  by  acidulation  with  acetic  acid  and  sub- 
sequent filtration,  or  from  ox-gall  by  precipitation  with  alcohol,  after- 
wards dissolving  in  water,  and  again  precipitating  by  means  of  acetic 
acid.  It  can  also  be  obtained  from  mucus  by  diluting  it  with  water,  fil- 
tering, treating  the  insoluble  portion  with  weak  caustic  alkali,  and  pre- 
cipitating the  mucus  with  acetic  acid. 

Properties. — Mucin  has  a  ropy  consistency.  It  is  precipitated  by  al- 
cohol and  by  mineral  acids,  but  dissolved  by  excess  of  the  latter.  It  is 
•dissolved  by  alkalies  and  in  lime  water.  It  gives  the  proteid  reaction 
with  Millon's  reagent  and  nitric  acid,  but  not  with  copper  sulphate. 
Neither  mercuric  chloride  nor  tannic  acid  gives  a  precipitate  with  it  (?). 
It  does  not  dialyze. 

(c)  Elastin  is  found  in  elastic  tissue,  in  theligamenta  subflava,  liga- 
mentum  nuchae,  etc. 

Take  the  fresh  ligamentum  nucha?  of  an  ox,  cut  in  pieces,  and  boil 
in  alcohol  and  ether  to  remove  the  fat.  Remove  the  gelatin  by  boiling 
for  some  hours  in  water.  Boil  the  residue  with  acetic  acid  for  some 
time,  and  remove  the  acid  by  boiling  in  water,  then  boil  with  caustic 
soda  until  it  begins  to  swell.  Remove  the  alkali,  and  leave  it  in  cold 
hydrochloric  acid  for  twenty-four  hours,  and  afterwards  wash  with 
water. 

Properties. — It  is  insoluble,  but  swells  up  both  in  cold  and  hot  water. 
Is  soluble  in  strong  caustic  soda.  It  is  precipitated  by  tannic  acid;  does 
not  gelatinize.  Gives  the  proteid  reactions  with  strong  nitric  acid  and 
ammonia,  and  imperfectly  with  Millon's  reagent.  Yields  leucin  on  boil- 
ing with  strong  sulphuric  acid. 

(d)  Chondrin  is  found  in  cartilage. 

It  is  prepared  by  boiling  small  pieces  of  cartilage  for  several  hours, 
and  filtering.  The  opalescent  filtrate  will  form  a  jelly  on  cooling. 
Chondrin  is  precipitated  from  the  warm  filtrate  on  addition  of  acetic 
acid. 

Properties. — It  is  soluble  in  hot  water,  and  in  solutions  of  neutral 
salts,  e.g.,  sulphate  of  sodium,  in  dilute  mineral  acids,  caustic  potash, 
and  soda.  Insoluble  in  cold  water,  alcohol,  and  ether.  It  is  precipitated 
from  its  solutions  by  dilute  mineral  acids  (excess  redissolves  it),  by  alum, 
by  lead  acetate,  by  silver  nitrate,  and  by  chlorine  water.  On  boiling  with 
strong  hydrochloric  acid,  it  yields  grape-sugar,  and  certain  nitrogenous 
substances.  Prolonged  boiling  in  dilute  acids,  or  in  water,  destroys  its 
jpower  of  forming  a  jelly  on  cooling. 

(e)  Keratin  is  obtained  from  hair,  nails,  and  dried  skin.  It  con- 
tains sulphur  evidently  only  loosely  combined. 

(3.)  Decomposition  Nitrogenous  products. — These  are  formed  by  the 
chemical  actions  which  go  on  in  digestion,  secretion,  and  nutrition. 


742  APPENDIX. 

Amido- Acids. 

Glycin,   Glycocol,   Glyco- )  p  tt  i™  _  /Ptt  /NH2     \ 
cin,  or  Amido-acetic  acid  j  °2  ^  1>Ua~  V       2\C0  OHJ' 

This  substance  occurs  in  the  body  in  combination  as  in  the  biliary 
acids,  but  is  never  free.  Glycocholic  acid,  when  treated  with  weak 
acids,  with  alkalies,  or  with  baryta  water,  splits  up  into  cholic  acid  and 
glycin,  or  amido-acetic  acid.  Thus:  C26  H43N06  +  H„0  =  C26  H40  0^ 
+  C2  HB  N02.  Glycocholic  acid  +  water  =  cholic  acid  +  glycin, 
and  under  similar  circumstances  Taurocholic  acid  splits  up  into  cholic 
acid  and  taurin:-C26  H45  03  NS02  +  H20  =  C26H40  05  +  C2  H7  NSO„ 
or  amido-isethionic.  Taurocholic  acid  +  water  =  cholic  acid  and 
taurin.  Glycin  occurs  also  in  hippuric  acid.  It  can  be  prepared  from 
gelatin  by  the  action  of  acids  or  alkalies;  it  can  also  be  obtained  from 
hippuric  acid. 

Sarcosin  or  Methyl )  n  tt  ATn  (     nxr  /NH  CH,\       T,  .    n  mMi 
Glycin,  [  W*M=  CH<C0  OH   )'     lt  1S  a  con" 

stituent  of  kreatin,  and  also  of  caffeine,  but  has  never  been  found  free  in 
the  human  body.  It  may  be  obtained  from  these  bodies  by  boiling  with 
baryta  water. 

LCcaproic  Addf0"  }  C^^0^  =  CH,CH2CH2CH,CH(NH2> 
CO  OH  occurs  normally  in  many  of  the  organs  of  the  body  and  is  a  pro- 
duct of  the  pancreatic  digestion  of  proteids.  It  is  present  in  the  urine 
in  certain  diseases  of  the  liver  in  which  there  is  loss  of  substance,  espe- 
cially in  acute  yellow  atrophy.  It  occurs  in  circular  oily  discs  or 
crystallizes  in  plates,  and  can  be  prepared  either  by  boiling  horn  shavings, 
or  any  of  the  gelatins  with  sulphuric  acid,  or  out  of  the  products  of 
pancreatic  digestion. 

Amido-sulphonic  Acids. 

TfSonicAAd,T  \  °>H<NS0-(  =  c^Xh  -  «"■?** 

of  the  bile  acid,  taurochloric  acid,  and  is  found  also  in  traces  in  the 
muscles  and  lungs.  It  has  been  prepared  synthetically  from  isethionic 
acid.     It  is  a  crystalline  substance,  very  stable. 

Benzoyl  Amido-acids. 

HSenzolgtydn,0r  |  CGHeNO3=(C0H5CONH  CH2COOH),  a  normal 
constituent  of  human  urine,  the  quantity  excreted  being  increased  by  a 
vegetable  diet,  and  therefore  it  is  present  in  greater  amount  in  the  urine 
of  herbivora.  It  may  be  decomposed  by  acids  into  glycin  and  benzoic 
acid.  It  crystallizes  in  semi-transparent  rhombic  prisms,  almost  insolu- 
ble in  cold  water,  soluble  in  boiling  water.     (See  also  p.  368.) 


APPENDIX.  743 

Tyrosin,  C9HuN03,  is  found  generally  together  with  leucin,  in 
certain  glands,  e.  g.,  pancreas  and  spleen;  and  chiefly  in  the  products  of 
pancreatic  digestion  or  of  the  putrefaction  of  proteids.  It  is  found  in 
the  urine  in  some  diseases  of  the  liver,  especially  acute  yellow  atrophy. 
It  crystallizes  in  fine  needles,  which  collect  into  feathery  masses.  It 
gives  the  proteid  test  with  Millon's  reagent,  and  heated  with  strong 
sulphuric  acid,  on  the  addition  of  ferric  chloride  gives  a  violet  color. 

Lecithin,  C4„Hh4PN09,  is  a  complex  nitrogenous  fatty  body,  contain- 
ing phosphorus,  which  has  been  found  mixed  with  cerebrin  and  oleo- 
phosphoric  acid  in  the  brain.  It  is  also  found  in  blood,  bile  and  serous 
fluids,  and  in  larger  quantities  in  nerves,  pus,  yelk  of  egg,  semen,  and 
Avhite  blood-corpuscles.  On  boiling  with  acids  it  yields  cholin,  glycero- 
phosphoric  acid,  palmic  and  oleic  acids. 

Cerebrin,  CnH33N03,  is  found  in  nerves,  pus  corpuscles,  and  in  the 
brain.  Its  chemical  constitution  is  not  known.  It  is  a  light  amorphous 
powder,  tasteless  and  odorless.  Swells  up  like  starch  when  boiled  with 
wa+,er,  and  is  converted  by  acids  into  a  saccharine  substance  and  other 
bodies.     The  so-called  Protagon  is  a  mixture  of  lecithin  and  cerebrin. 

Urea  and  its  Allies. 

Urea  or  Carbamide,  CON2H4,  is  the  last  product  of  the  oxidation 
of  the  albuminous  tissues  of  the  body  and  of  the  albuminous  foods.  It 
occurs  as  the  chief  nitrogenous  constituent  of  the  urine  of  man,  about  2 
to  3  per  cent,  and  of  some  other  animals.  It  has  been  found  in  the 
blood  and  serous  fluids,  in  lymph,  and  in  the  liver. 

Properties. — Crystallizes  in  thiu  glittering  needles,  or  in  prisms  with 

pyramidal  ends.     Easily  soluble  in  water  and  alcohol,  insoluble  in  ether 

It  may  be  produced  artificially  by  treating  carbonyl  chloride  (C0C1„)  with 

/OP  IT 
ammonia;  or  by  heating  ethyl  carbonate  with  ammonia  00^ Xrrtr'   + 

2NHa     =     C0N.,H42CoH60;     by     heating    carbonate     of    ammonium 

CO  /o^|j  =  00NaH,  +  H,0;  by  adding  water  to  cyanamide  CN.NH,, 

or  by  evaporating  ammonium  cyanate  in  aqueous  solution.  When  heated 
with  water  in  a  sealed  tube  to  100°  C.  or  on  allowing  urine  to  stand, 
urea  splits  up  into  carbonic  acid  and  ammonia;  when  heated  to  a  high 
temperature  urea  loses  ammonia  and  first  yields  biuret  C„H5N30.„  and 
after  cyanuric  acid,  C3H303N3.  It  is  decomposed  by  sodium  hypochlo- 
rite or  hypobromite,  or  by  nitrous  acid  with  evolution  of  N.  It  forms 
compounds  with  acids,  of  which  the  chief  are  urea  hydrochloride  CII4 
N90.HC1;  urea  nitrate,  CH4N2OHN03;  and  urea  phosphate  CII^O. 
H3P04.  It  forms  compounds  with  metals  such  as  HgO.CH4N.jO;  with 
silver  CH„N30  Ag2;  and  with  salts  such  as  HgCla. 

Urea  is  isomeric  with  ammonium  cyanate  C^^wtt  from  which  it 
was  first  artificially  prepared. 

Kreatin,  C4HaN3On_,  is  one  of  the  primary  products  of  muscular  dis- 


744  APPENDIX. 

integration.  It  is  always  found  in  the  juice  of  muscle.  It  is  generally 
decomposed  in  the  blood  into  urea  and  kreatinin,  and  seldom,  unless 
under  abnormal  circumstances,  appears  as  such  in  the  urine.  Treated 
with  either  sulphuric  or  hydrochloric  acid,  it  is  converted  into  kreatinin; 
thus — 

C4H9N302  =  C4H7]Sr30  +  H20. 

It  has  been  made  synthetically  by  bringing  together  cyanimide  and 
sarcosine. 

Kreatinin,  C4H7]Sr30,  is  present  in  human  urine,  derived  from  oxida- 
tion of  kreatin.     It  does  not  appear  to  be  present  in  muscle. 

Uric  Acid,  C6H4N"403,  occurs  in  the  urine,  sparingly  in  human  urine, 
abundantly  in  that  of  birds  and  reptiles,  where  it  represents  the  chief 
nitrogenous  decomposition  product.  It  occurs  also  in  the  blood,  spleen, 
liver,  and  sometimes  is  the  only  constituent  of  urinary  calculi.  It  is 
probably  converted  in  the  blood  into  urea  and  carbonic  acid.  It  gener- 
ally occurs  in  urine  in  combination  with  bases,  forming  urates,  and 
never  free  unless  under  abnormal  conditions.  A  deposit  of  urates  may 
occur  when  the  urine  is  concentrated  or  extremely  acid,  or  when,  as 
during  febrile  disorders,  the  conversion  of  uric  acid  into  urea  is  incom- 
pletely performed. 

Properties. — Crystallizes  in  many  forms,  of  which  the  most  common 
are  smooth,  transparent,  rhomboid  plates,  diamond-shaped  plates,  hexa- 
gonal tables,  etc.  Very  insoluble  in  water,  and  absolutely  so  in  alcohol 
and  ether.  Dried  with  strong  nitric  acid  in  a  water  bath,  a  compound 
is  formed  called  alloxan,  which  gives  a  beautiful  violet  red  with  ammo- 
nium hydrate  (murexide),  and  a  blue  color  with  potassium  hydrate.  It 
is  easily  precipitated  from  its  solutions  by  the  addition  of  a  free  acid. 
It  forms  both  acid  and  neutral  salts  with  bases.  The  most  soluble  urate 
is  lithium  urate. 

Composition. — Very  uncertain;  has  been  however  recently  produced 
artificially,  but  it  is  not  easily  decomposed;  it  may  be  regarded  as  diure- 
ide  of  tartronic  acid.     The  chief  product  of  its  decomposition  is  urea. 

Guanin,  C&H5N60,  has  been  found  in  the  human  liver,  spleen,  and 
faeces,  but  does  not  occur  as  a  constant  product. 

Xanthin,  C6H4N402,  has  been  obtained  from  the  liver,  spleen,  thy- 
mus, muscle,  and  the  blood.  It  is  found  in  normal  urine,  and  is  a  con- 
stituent of  certain  rare  urinary  calculi. 

Hypoxanthin,  C&H4N40,  or  sarhin,  is  found  in  juice  of  flesh,  in  the 
spleen,  thymus,  and  thyroid. 

Allantoin,  C4H0N4O3,  found  in  the  allantoic  fluid  of  the  foetus,  and 
in  the  urine  of  animals  for  a  short  period  after  their  birth.  It  is  one  of 
the  oxidation  products  of  uric  acid,  which  on  oxidation  gives  urea. 

In  addition  to  the  above  compounds  and  probably  related  to  them, 


APPENDIX.  745 

are  certain  coloring  and  excrementitious   matters,  which  are  also  most 
likely  distinct  decomposition  compounds. 

Pigments,  etc. 

Bilirubin,  C9H9N02,  is  the  best  known  of  the  bile  pigments.  It  is 
best  made  by  extracting  inspissated  bile  or  gall  stones  with  water  (which 
dissolves  the  salts,  etc.),  then  with  alcohol,  which  takes  out  cholesterin, 
fatty,  and  biliary  acids.  Hydrochloric  acid  is  then  added,  which  decom- 
poses the  lime  salt  of  bilirubin  and  removes  the  lime.  After  extracting 
with  alcohol  and  ether,  the  residue  is  dried  and  finally  extracted  with 
chloroform.  It  crystallizes  of  a  bluish-red  color.  It  is  allied  in  compo- 
sition to  hematin. 

Biiiverdin,  C8H9N02,  is  made  by  passing  a  current  of  air  through  an 
alkaline  solution  of  bilirubin,  and  by  precipitation  with  hydrochloric 
acid.     It  is  a  green  pigment. 

Bilifuscin,  C9HnN03,  is  made  by  treating  gall  stones  with  ether, 
then  with  dilute  acid,  and  extracting  with  absolute  alcohol.  It  is  a  non- 
cry  stallizable  brown  pigment. 

Biliprasin  is  a  pigment  of  a  green  color,  which  can  be  obtained  from 
gall  stones. 

Bilihumin  (Staedeler)  is  a  dark  brown  earthy-looking  substance,  of 
which  the  formula  is  unknown. 

Urochrome  (see  p.  368). 

Urobilin  occurs  in  bile  and  in  urine,  and  is  probably  identical  with 
■stercobilin,  which  is  found  in  the  faeces. 

Uroerythrin  is  one  of  the  coloring  matters  of  the  urine.  It  is  orange 
red  and  contains  iron. 

Melanin  is  a  dark  brown  or  black  material  containing  iron,  occur- 
ring in  the  lungs,  bronchial  glands,  the  skin,  hair,  and  choroid. 

Choletelin  (p.  369). 

Haematin  has  been  fully  treated  of>  p.  86,  et  seq. 

Indican  is  supposed  to  exist  in  the  sweat  and  urine.  It  has  not,  how- 
ever, been  satisfactorily  isolated. 

Indigo,  CHH6N90,  is  formed  from  indican,  and  gives  rise  to  the 
bluish  color  which  is  occasionally  met  with  in  the  sweat  and  urine  (also 
369). 

Indol,  C8H2N,  is  found  in  the  faeces,  and  is  formed  either  by  decom- 
position of  indigo,  or  of  the  proteid  food  materials.  It  gives  the  char- 
acteristic disagreeable  smell  to  faeces  (see  p.  272). 

(4.)  Nitrogenous  Bodies  of  Uncertain  Nature. 

Ferments  are  bodies  which  possess  the  property  of  exciting  chemical 
change  in  matter  with  which  they  come  in  contact.     They  are  at  present 


746  APPENDIX. 

divided  into  two  classes,  called  (1)  organized,  and  (2)  unorganized  or 
soluble. 

(1.)  Of  the  organized,  yeast  may  be  taken  as  an  example.  Its  activity 
depends  upon  the  vitality  of  the  yeast  cell,  and  disappears  as  soon  as  the 
cell  dies,  neither  cau  any  substance  be  obtained  from  the  yeast  by  means 
of  precipitation  with  alcohol  or  in  any  other  way  which  has  the  power  of 
exciting  the  Ordinary  change  produced  by  yeast.  The  action  of  micro- 
organisms in  the  alimentary  canal  and  elsewhere  is  also  an  example  of 
the  same  nature. 

(2.)  Unorganized  or  soluble  ferments  are  those  which  are  found  in 
secretions  of  glands,  or  are  produced  by  chemical  changes  in  animal  or 
vegetable  cells  in  general;  when  isolated  they  are  colorless,  tasteless, 
amorphous  solids  soluble  in  water  and  glycerin,  and  precipitated  from 
the  aqueous  solutions  by  alcohol  and  acetate  of  lead.  Chemically  many 
of  these  are  said  to  contain  nitrogen. 

Mode  of  action. — Without  going  into  the  theories  of  how  these  unor- 
ganized ferments  act,  it  will  suffice  to  mention  that: 

(1.)  Their  activity  does  not  depend  upon  the  actual  amount  of  the 
ferment  present.  (2.)  That  the  activity  is  destroyed  by  high  tempera- 
ture, and  various  concentrated  chemical  reagents,  but  increased  by  mode- 
rate heat,  about  40°  C,  and  by  weak  solutions  of  either  an  acid  or  alka- 
line fluid.  (3.)  The  ferments  themselves  appear  to  undergo  no  change 
in  their  own  composition,  and  waste  very  slightly  during  the  process. 

Varieties. — The  chief  classes  of  unorganized  ferments  are: — 

(1.)  Amylolytic,  which  possess  the  property  of  converting  starch 
into  glucose.  They  add  a  molecule  of  water,  and  may  be  called  hydro- 
lytic.     The  probable  reaction  is  given,  p.  234. 

The  principal  amylolytic  ferments  are  Ptyalin,  found  in  the  saliva, 
and  a  ferment,  probably  distinct,  in  the  pancreatic  juice,  called  Amy- 
lopsin.  These  both  act  in  an  alkaline  medium.  Amylolytic  ferments 
have  been  found  in  the  blood  and  elsewhere. 

(2.)  Proteolytic  convert  proteids  into  peptones.  The  nature  of  their 
action  is  probably  hydrolytic.  The  proteolytic  ferments  of  the  body  are 
called  Pepsin,  acting  in  an  acid  medium  from  the  gastric  juice.  Trypsin, 
acting  in  an  alkaline  medium  from  the  pancreatic  juice.  The  Succus 
entericus  is  said  to  contain  a  third  such  ferment. 

(3.)  Inversive,  which  convert  cane  sugar  or  saccharose  into  grape 
sugar  or  glucose.  Such  a  ferment  was  found  by  Claude  Bernard  in  the 
Succus  entericus;  and  probably  exists  also  in  the  stomach  mucus. 

(4.)  Ferments  which  act  upon  fats, — Such  a  body,  called  Steap- 
sin,  has  been  found  in  pancreatic  juice. 

(5. )  Milk-curdling  ferments. — It  has  been  long  known  that  rennet, 
a  decoction  of  the  fourth  stomach  of  a  calf,  in  brine,  possessed  the  power 
of  curdling  milk.     This  power  does  not  depend  upon  the  acidity  of  the 


APPENDIX.  747 

gastric  juice,  since  the  curdling  will  take  place  in  a  neutral  or  alkaline 
medium;  neither  does  it  depend  upon  the  pepsin,  as  pure  pepsin  scarcely 
curdles  milk  at  all,  and  the  rennet  which  rapidly  curdles  milk  has  a  very 
feeble  proteolytic  action.  From  this  and  other  evidence  it  is  believed 
that  a  distinct  milk-curdling  ferment  exists  in  the  stomach.  W.  Roberts 
has  shown  that  a  similar  but  distinct  ferment  exists  in  pancreatic  extract, 
which  acts  best  in  an  alkaline  medium,  next  best  in  are  acid  medium, 
and  worst  in  a  neutral  medium.  The  ferment  of  rennet  acts  best  in  an 
acid  medium,  and  worst  in  an  alkaline,  the  reaction  ceasing  if  the  alka- 
linity be  more  than  slight. 

In  addition  to  the  above  ferments,  many  others  most  likely  exist  in 
the  body,  of  which  the  following  are  the  most  important: 

(6.)  Fibrin-forming  ferment  (Schmidt),  (see  p.  64,  et  seq.),  found 
in  the  blood,  lymph  and  chyle. 

(7.)  A  ferment  which  converts  glycogen  into  glucose  in  the 
liver;  being  therefore  an  amylolytic  ferment. 

(8.)  Myosin  ferment. 

(b.)   Organic  non-nitrogenous  bodies  consist  of 

(1.)  Oils  and  Fats. 

Most  oils  and  fats  are  mixtures  of  palmitin  C61  H90  06,  stearin  C57- 
Hn0  0„,  and  olein  C67  H104  06,  in  different  proportions.  They  are  formed 
by  the  union  of  fatty  acid  radicals  with  the  triatomic  alcohol,  Glycerin 
C3  H6  (OH)„  and  are  ethereal  salts  of  that  alcohol.  The  radicals  are  ClB- 
H35  0,  CI6  H31  0,  and  CIh  H33  0,  respectively.  Human  fat  consists  of  a 
mixture  of  palmitin,  stearin,  and  olein,  of  which  the  two  former  con- 
tribute three-quarters  of  the  whole.  Olein  is  the  only  liquid  consti- 
tuent. 

General  characteristics. — Insoluble  in  water  and  in  cold  alcohol;  solu- 
ble in  hot  alcohol,  ether,  and  chloroform.  Colorless  and  tasteless;  easily 
decomposed  or  saponified  by  alkalies  or  superheated  steam  into  glycerin 
and  the  fatty  acids. 

Cholesterin,  C.,(.  H44  0,  is  the  only  alcohol  which  has  been  found  in 
the  body  in  a  free  state.  It  has  been  called  a  non-saponifiable  fat.  It 
occurs  in  small  quantities  in  the  blood  and  various  tissues,  and  forms 
the  principal  constituent  of  gall-stones.  It  is  found  in  dropsical  fluids, 
especially  in  the  contents  of  cysts,  in  disorganized  eyes,  and  in  plants 
(especially  peas  and  beans).  It  is  soluble  in  ether,  chloroform,  or  benzol. 
It  crystallizes  in  white  feathery  needles.  See  also  under  the  head  of  the 
constituents  of  the  bile. 

Excretin  (Marcet).  and  Stercorin  (Flint),  are  crystalline  fatty  bodies 
which  have  been  isolated  from  the  fa?ces. 


748  appendix. 

(2.)  Carbo-hydrates  or  Amyloids. 

Carbo-hydrates  are  bodies  composed  of  six  or  twelve  atoms  of  carbon 
•with  hydrogen  and  oxygen,  the  two  latter  elements  being  in  the  propor- 
tion to  form  water. 

Amyloses,  Cfl  H10  06,  Starch,  Dextrin,  Glycogen,  Inulin,  Cellulose, 
Gum. 

Saccharoses,  C1S  HOT  Ou,  Saccharose,  or  Cane  sugar,  Lactose,  Mal- 
tose, Melitose. 

Glucoses,  C6  H12  06,  Dextrose  or  Grape  sugar,  Lasvulose  or  Fruit- 
sugar,  Inosite,  Mannitose. 

Of  these  the  most  important  are: 

(a)  Starch  (C6  HI0  05)  which  is  contained  in  nearly  all  plants,  and 
in  many  seeds,  roots,  stems,  and  some  fruits. 

Characters. — It  is  a  soft,  white  powder  composed  of  granules  having 
an  organized  structure,  consisting  of  granulose  (soluble  in  water)  con- 
tained in  a  coat  of  cellulose  (insoluble  in  water);  the  shape  and  size  of 
the  granules  varying  according  to  the  source  whence  the  starch  has  been 
obtained. 

Tests. — It  is  insoluble  in  cold  water,  in  alcohol,  and  in  ether;  it  is 
soluble  after  boiling  for  some  time,  and  may  be  filtered,  in  consequence 
of  the  swelling  up  of  the  granulose,  which  bursts  the  cellulose  coat,  and 
becoming  free,  is  entirely  dissolved  in  water.  This  solution  is  a  solution 
of  soluble  starch  or  amydin. 

It  gives  a  blue  coloration  with  iodine,  which  disappears  on  heating 
and  returns  on  cooling. 

It  is  converted  into  dextrin  and  grape-sugar  by  diastase  or  by  boil- 
ing with  dilute  acids. 

(b)  Glycogen. 

Glycogen,  usually  obtained  from  the  livers,  is  also  present  to  a  con- 
siderable extent  in  the  muscles  of  very  young  animals.  In  order  to 
prepare  it  in  considerable  amount,  it  is  best  to  use  the  liver  of  a  rabbit. 
The  animal  should  be  large,  and  should  have  been  well  fed  on  a  diet  of 
gram  and  sugar  for  some  days,  or  even  weeks,  previously.  It  should 
have  had  a  full  meal  of  grain,  carrots,  and  sugar,  about  two  hours  be- 
fore it  is  killed,  in  order  that  it  may  be  in  full  digestion.  The  rabbit  is 
killed  either  by  decapitation,  or  by  a  blow  on  the  head,  and  the  abdo- 
men is  then  rapidly  opened,  and  the  liver  is  torn  out,  is  chopped  up  as 
quickly  as  possible  with  the  knife,  and  is  thrown  into  boiling  water.  It 
is  important  that  this  operation  should  be  performed  within  half  a 
minute  of  the  death  of  the  animal,  and  that  the  water  should  not  be  al- 
lowed to  fall  below  the  boiling  point.  The  liver  is  to  remain  in  the  hot 
water  for  five  minutes;  it  is  then  poured  into  a  mortar,  and  reduced  to 
a  pulp,  and  is  again  boiled  for  ten  minutes.  The  liquid  is  filtered,  and 
the  filtrate  is  rapidly  cooled.  The  albuminous  substances  in  the  cold 
filtrate  are  precipitated  by  adding  potassio-mercuric  iodine  and  dilute  hy- 


AIM'KNDIX.  74rl> 

drogen  chloride  alternately  as  long  as  any  precipitate  is  produced.  The 
mixture  is  then  stirred,  is  allowed  to  stand  for  five  minutes,  and  is  fil- 
tered. Alcohol  is  added  to  this  second  filtrate  until  glycogen  is  preci- 
pitated, which  occurs  after  about  60  per  cent  of  absolute  alcohol  has 
been  added.  The  precipitate  is  then  filtered  off,  and  is  washed  with 
weak  spirit,  strong  spirit,  absolute  alcohol  (two  or  three  times),  and 
finally  with  ether.  It  is  then  dried  on  a  glass  plate  at  a  moderate  heat, 
and,  if  pure,  should  remain  as  a  white  amorphous  powder.  If  the  water 
has  not  been  completely  removed,  the  glycogen  will  form  a  gummy  mass; 
in  this  case  it  must  again  be  treated  with  absolute  alcohol. 

Properties. — It  is  freely  soluble  in  water,  and  its  solution  looks  opa- 
lescent; it  gives  a  port-wine  coloration  with  iodine,  which  disappears  on 
heating  and  returns  on  cooling. 

It  is  insoluble  in  absolute  alcohol  and  in  ether. 

It  exists  in  the  liver  during  life,  but  very  soon  after  death  is  changed 
into  sugar.  It  is  converted  into  sugar  by  diastase  ferments,  or  by  boil- 
ing with  dilute  acids. 

(c)  Dextrin. — This  substance  is  made  in  commerce  by  heating  dry 
potato  starch  to  a  temperature  of  400°.  It  is  also  produced  in  the  pro- 
cess of  the  conversion  of  starch  into  sugar  by  diastase,  and  by  the  sali- 
vary and  pancreatic  ferments. 

Properties. — A  yellowish  amorphous  powder,  soluble  in  water,  but 
insoluble  in  absolute  alcohol  and  in  ether. 

It  corresponds  almost  exactly  in  tests  with  glycogen;  but  one  variety 
(achroo-dextrin)  does  not  give  the  port-wine  coloration  with  iodine. 

(d)  Glucose  occurs  widely  diffused  in  the  vegetable  kingdom,  in 
diabetic  urine,  in  the  blood,  etc.;  it  is  usually  obtained  from  grape-juice, 
honey,  beet-root,  or  carrots.  It  really  is  a  mixture  of  two  isomeric 
bodies,  Dextrose  or  grape-sugar,  which  turns  a  ray  of  polarized  light  to 
the  right,  and  Lmvulose  or  fruit-sugar,  which  turns  the  ray  to  the  left. 

Properties. — It  is  easily  soluble  in  water;  not  so  sweet  as  cane-sugar; 
the  relation  of  its  sweetness  to  that  of  cane-sugar  is  as  3  to  5. 

It  is  not  so  easily  charred  by  strong  sulphuric  acid  as  cane-sugar. 

It  is  not  entirely  soluble  in  alcohol. 

Tests. — (i.)  Trommer's. — This  test  depends  upon  the  power  sugar 
possesses  of  reducing  copper  salts  to  their  suboxide.  It  is  done  in  the 
following  way: — An  excess  of  caustic  potash  and  then  a  solution  of  cop- 
per sulphate,  drop  by  drop,  is  added  to  the  solution,  containing  the 
sugar  in  a  test-tube,  as  long  as  the  blue  precipitate  which  forms  redis- 
solves  on  shaking  the  tube.  The  upper  portion  of  the  fluid  is  then 
heated,  and  a  yellowish-brown  precipitate  of  copper  suboxide  appears. 

(ii.)  Moore's. — If  a  solution  of  sugar  in  a  test-tube  is  boiled  with 
caustic  potash,  a  brown  coloration  appears. 

(iii.)  Fermentation. — If  a  solution  of  sugar  be  kept  in  the  warm 


750  APPENDIX. 

plate  for  a  time  after  the  addition  of  yeast,  the  sugar  is  converted  into 
alcohol  and  carbon  dioxide  (C6H1206  =  2C2H5OH  +  2C02). 

(iv.)  Bottcher's  test. — A  little  bismuth  oxide  or  subnitrate  and  an 
excess  of  caustic  potash  are  added  to  the  solution  in  a  test-tube,  and  the 
mixture  is  heated;  the  solution  becomes  at  first  gray  and  then  black. 

(v.)  Picric  acid  test. — To  the  solution  about  a  fourth  of  its  bulk  of 
picric  acid  (saturated  solution)  and  an  equal  quantity  of  caustic  potash 
are  added,  and  the  solution  is  boiled;  the  liquid  becomes  of  a  very  deep 
coffee-brown. 

(e)  Lactose  is  contained  in  milk  (p.  338). 

Properties. — It  is  less  soluble  in  water  than  glucose;  not  sweet,  and 
is  gritty  to  the  taste;  but  it  is  insoluble  in  absolute  alcohol.  Undergoes 
alcoholic  fermentation  with  extreme  difficulty;  gives  the  tests  similar  to 
glucose,  but  less  readily. 

(f)  Inosite. — Inosite  is  a  non-fermentible  variety  of  glucose  occur- 
ring in  the  heart  and  voluntary  muscles,  as  well  as  in  beans  and  other 
plants.  It  crystallizes  in  the  form  of  large,  colorless  monoclinic  tables, 
which  are  soluble  in  water,  but  insoluble  in  alcohol  or  ether.  Inosite 
may  be  detected  by  evaporating  the  solution  containing  it  nearly  to  dry- 
ness, and  by  then  adding  a  small  drop  of  a  solution  of  mercuric  nitrate, 
and  afterwards  evaporating  carefully  to  dryness,  a  yellowish-white  residue 
is  obtained;  on  further  cautiously  heating,  the  yellow  changes  to  a  deep 
rose-color,  which  disappears  on  cooling,  bat  reappears  on  heating.  If 
the  inosite  be  almost  pure,  its  solution  may  be  evaporated  nearly  to  dry- 
ness. After  the  addition  of  nitric  acid,  the  residue  mixed  with  a  little 
ammonia  and  calcium  chloride,  and  again  evaporated,  yields  a  rose-red 
coloration. 

(g)  Maltose  is  formed  in  the  conversion  of  starch  into  glucose  by 
the  saliva  and  pancreatic  fluids.  It  is  also  formed  by  the  action  of  malt 
upon  starch  by  the  ferment  diastase,  and  in  the  formation  of  glucose 
from  starch.  It  is  converted  into  dextrin  by  dilute  sulphuric  acid.  It 
is  dextro-rotatory;  ferments  with  yeast;  reduces  copper  salts,  and  crys- 
tallizes in  fine  needles. 

Monatomic  Fatty  Acids. 

Formic  CH202,  acetic  C2H402,  and  propionic  C3H602,  acids  are  pres- 
ent in  sweat,  but  normally  in  no  other  human  secretion.  They  have 
been  found  elsewhere  in  diseased  conditions.  Butyric  acid,  C4H802,  is 
found  in  sweat.  Various  others  of  these  acids  have  been  obtained  from 
blood,  muscular  juice,  faeces,  and  urine. 

Diatomic  Fatty  Acids. 

Lactic  acid,  C3  Hs  03,  exists  in  a  free  state  in  muscle  plasma,  and 
is  increased  in  quantity  by  muscular  contraction,  is  never  contained  in 


APPENDIX.  751 

healthy  blood,  and  when  present  in  abnormal  amount  seems  to  produce 
rheumatism. 

Oxalates  are  present  in  the  urine  in  certain  diseases,  and  after  drink- 
ing certain  carbonated  beverages,  and  after  eating  rhubarb,  etc. 

Aromatic  Series. 


Benzoic, C7  H  0 

Phenol, C.H.O' 


Benzoic  acid,  C3  H6  02,  is  always  found  in  the  urine  of  herbivora, 
and  can  be  obtained  from  stale  human  urine.  It  does  not  exist  free  else- 
where. 

Phenol. — Phenyl  alcohol  or  carbolic  acid  exists  in  minute  quantity  in 
human  urine.     It  is  an  alcohol  of  the  aromatic  series. 

2.  Inorganic   Principles. 

The  inorganic  proximate  principles  of  the  human  body  are  numerous. 
They  are  derived,  for  the  most  part,  directly  from  food  and  drink,  and 
pass  through  the  system  unaltered.  Some  are,  however,  decomposed  on 
their  way,  as  chloride  of  sodium,  of  which  only  four-fifths  of  the  quantity 
ingested  are  excreted  in  the  same  form;  and  some  are  newly  formed 
within  the  body, — as  for  example,  a  part  of  the  sulphates  and  carbonates, 
and  some  of  the  water. 

Much  of  the  inorganic  saline  matter  found  in  the  body  is  a  necessary 
constituent  of  its  structure,  as  necessary  in  its  way  as  albumin  or  any 
other  organic  principle;  another  partis  important  in  regulating  or  modi- 
fying various  physical  processes,  as  absorption,  solution,  and  the  like; 
while  a  part  must  be  reckoned  only  as  matter,  which  is,  so  to  speak,  acci- 
dentally present,  whether  derived  from  the  food  or  the  tissues,  and  which 
will,  at  the  first  opportunity,  be  excreted  from  the  body. 

Gases.— The  gaseous  matters  found  in  the  body  are  Oxygen,  Hydro- 
gen, Nitrogen,  Carburetted  and  Sulphuretted  hydrogen,  and  Carbonic 
acid.  The  first  three  have  been  referred  to  (p.  732).  Carburetted  and 
sulphuretted  hydrogen  are  found  in  the  intestinal  canal.  Carbonic 
acid  is  present  in  the  blood  and  other  fluids,  and  is  excreted  in  large 
quantities  by  the  lungs,  and  in  very  minute  amount  by  the  skin.  It 
has  been  specially  considered  in  the  chapters  on  Respiration  and  else- 
where. 

Water,  the  most  abundant  of  the  proximate  principles,  forms  a  large 
proportion,  more  than  two-thirds  of  the  weight  of  the  whole  bod  v.  Its 
relative  amount  in  some  of  the  principal  solids  and  fluids  of  the  bodv  is 
shown  in  the  following  table  (quoted  by  Dalton,  from  Robin  and  Ver- 
deil's  table,  compiled  from  various  authors): — 


752 


appendix. 
Quantity  of  Water  in  1000  Parts. 


100 

Bile,      . 

.     880 

130 

Milk,        .      ^  . 

887 

550 

Pancreatic  juice,  . 

.     900 

750 

Urine, 

936 

768 
789 

Lymph, 
Gastric  juice,    . 

.  960 
975 

795 
805 

Perspiration, 
Saliva, 

.  986 
995 

Teeth,  . 

Bones,      .... 

Cartilage, 

Muscles,    .... 

Ligament,     . 

Brain,       .... 

Blood, 

Synovia,  .... 

Uses  of  the  Water  of  the  Body. — The  importance  of  water  as 
a  constituent  of  the  animal  body  may  be  assumed  from  the  preceding 
table,  and  is  shown  in  a  still  more  striking  manner  by  its  withdrawal. 
If  any  tissue,  as  muscle,  cartilage,  or  tendon,  be  subjected  to  heat  suffi- 
cient to  drive  off  the  greater  part  of  its  water,  all  its  characteristic  physi- 
cal properties  are  destroyed;  and  what  was  previously  soft,  elastic,  and 
flexible,  becomes  hard  and  brittle,  and  horny,  so  as  to  be  scarcely  recog- 
nizable. 

In  all  the  fluids  of  the  body — blood,  lymph,  etc. — water  acts  the  part 
of  a  general  solvent,  and  by  its  means  alone  circulation  of  nutrient  mat- 
ter is  possible .  It  is  the  medium  also  in  which  all  fluid  and  solid  ali- 
ments are  dissolved  before  absorption,  as  well  as  the  means  by  which  all, 
except  gaseous,  excretory  products  are  removed.  All  the  various  processes 
of  secretion,  transudation,  and  nutrition  depend  of  necessity  on  its  pres- 
ence for  their  performance. 

Source. — The  greater  part,  by  far,  of  the  water  present  in  the  body 
is  taken  into  it  as  such  from  without,  in  the  food  and  drink.  A  small 
amount,  however,  is  the  result  of  the  chemical  union  of  hydrogen 
with  oxygen  in  the  blood  and  tissues.  The  total  amount  taken  into' 
the  body  every  day  is  about  4£  lbs.  ;  while  an  uncertain  quantity 
(perhaps  \  to  £  lb.)  is  formed  by  chemical  action  within  it.  (Dal- 
ton.) 

Loss. — The  loss  of  water  from  the  body  is  intimately  connected 
with  excretion  from  the  lungs,  skin,  and  kidneys,  and  to  a  less  extent, 
from  the  alimentary  canal.  The  loss  from  these  various  organs  may  be 
thus  apportioned  (quoted  by  Dalton  from  various  observers). 

From  the  Alimentary  canal  (faeces), 
"  Lungs, 

"  Skin  (perspiration), 

"  Kidneys  (urine),    . 

100 

Sodium  and  Potassium  Chlorides  are  present  in  nearly  all  parts 
of  the  body.  The  former  seems  to  be  especially  necessary,  judging  from 
the  instinctive  craving  for  it  on  the  part  of  animals  in  whose  food  it  is 


4 

per  cent. 

.  20 

t( 

30 

a 

.  46 

a 

APPENDIX.  753 

deficient,  and  from  the  diseased  condition  which  is  consequent  on  its 
withdrawal.  In  the  blood,  the  quantity  of  sodium  chloride  is  greater 
than  that  of  all  its  other  saline  ingredients  taken  together.  In  the  mus- 
cles, on  the  other  hand,  the  quantity  of  sodium  chloride  is  less  than  that 
of  the  chloride  of  potassium. 

Calcium  Fluoride,  in  minute  amount,  is  present  in  the  bones  and 
teeth,  and  traces  have  been  found  in  the  blood  and  some  other  fluids. 

Calcium,  Potassium,  Sodium,  and  Magnesium  Phosphates 
are  found  in  nearly  every  tissue  and  fluid.  In  some  tissues — the  bones 
and  teeth — the  phosphate  of  calcium  exists  in  very  large  amount  and  is 
the  principal  source  of  that  hardness  of  texture  on  which  the  proper 
performance  of  their  functions  so  much  depends.  The  phosphate  of 
calcium  is  intimately  incorporated  with  the  organic  basis  or  matrix,  but 
it  can  be  removed  by  acids  without  destroying  the  general  shape  of  the 
bone;  and,  after  the  removal  of  its  inorganic  salts,  a  bone  is  left  soft, 
tough,  and  flexible. 

Potassium  and  sodium  phosphates  with  the  carbonates,  maintain  the 
alkalinity  of  the  blood. 

Calcium  Carbonate  occurs  in  bones  and  teeth,  but  in  much  smaller 
quantity  than  the  phosphate.  It  is  found  also  in  some  other  parts.  The 
small  concretions  of  the  internal  ear  (otoliths)  are  composed  of  crystal- 
line calcium  carbonate,  and  form  the  only  example  of  inorganic  crystal- 
line matter  existing  as  such  in  the  body. 

Potassium  and  Sodium  Carbonates  are  found  in  the  blood,  and 
some  other  fluid  and  tissues. 

Potassium,  Sodium,  and  Calcium  Sulphates  are  met  with  in 
small  amount  in  most  of  the  solids  and  fluids. 

Silicon. — A  very  minute  quantity  of  silica  exists  in  the  urine,  and  in 
the  blood.  Traces  of  it  have  been  found  also  in  bones,  hair,  and  some 
other  parts. 

Iron. — The  especial  place  of  iron  is  in  haemoglobin,  the  coloring- 
matter  of  the  blood,  of  which  a  full  account  has  been  given  with  the 
chemistry  of  the  blood.  Peroxide  of  iron  is  found,  in  very  small  quan- 
tities, in  the  ashes  of  bones,  muscles,  and  many  tissues,  and  in  lymph 
and  chyle,  albumin  of  serum,  fibrin,  bile,  milk,  and  other  fluids;  and  a 
salt  of  iron,  probably  a  phosphate,  exists  in  the  hair,  black  pigment,  and 
other  deeply  colored  epithelial  or  horny  substances. 

Aluminium,  Manganese,  Copper,  and  Lead.— It  seems  most 
likely  that  in  the  human  body,  copper,  manganesium,  aluminium,  and 
lead  are  merely  accidental  elements,  which,  being  taken  in  minute  quan- 
tities with  the  food,  and  not  excreted  at  once  with  the  f;eces,  are  absorbed 
and  deposited  in  some  tissue  or  organ,  of  which,  however,  they  form  no 
necessary  part.  In  the  same  manner,  arsenic,  being  absorbed,  may 
deposited  in  the  liver  and  other  parts. 
48 


APPENDIX   B. 


MEASURES   OF  WEIGHT  (Avoirdupois). 


(Average* 


lbs. 

21 


Recent  Skeleton, 

Muscles  and  Tendons, 

Skin    and    Subcutaneou 

tissue,  . 

Blood,         .  .         11  to  14 

f Cerebrum,     .  •  2 

-d     •      J  Cerebellum,       .        - 
tfram   <j  P(mg  ftnd  Medulla 

[     oblongata, 


1G     5 


12 

-     1 


Eneephalon, 
Eyes,        .    '     . 
Heart,  .... 

Intestines,  small,     . 

"  large, 

Kidneys  (both), 
Larynx,  Trachea,  and  larger 
Bronchi, 


3     2 


10 

11* 
1 

10+ 


to  - 


Liver, 

Lungs  (both), 
(Esophagus,    . 
Ovaries  (both),    . 
Pancreas, 
Salivary  Clauds  (both  sides) 
If  to 
Stomach, 
Spinal  Cord,  divested  of  its 

nerves  and  membranes,  . 
Spleen,  .... 
Suprarenal  capsules  (both), 
£to 
Testicles  (both),  .  1|  to 
Thyroid  body  and  remains 

of  Thymus  gland, 
Tongue  and  Hyoid  bone,     . 
Uterus  (virgin),  .    -J  to 


bs. 

ozs. 

3 

8 

2 

10 

- 

11 

■2 

— 

3 

MEASURES   OF  LENGTH  (Average). 


Appendix  vermiformis,  3  to  - 

Bronchus,  right,  .  .  - 
left,    . 

Caecum,  - 

Duct,  common  bile,     .  .   - 

"  "  ejacuiatory,  £  to  - 
"  of  Cowper's  gland,  .  - 
"  hepatic,  .  .  .  - 
"     nasal,  - 

"  parotid,  .  .  .  - 
"     submaxillary,  .       - 

Epididymis,  .  .  .  - 
"  unravelled,      .     20 

Eustachian  tube,         .         .  - 

Fallopian  tube, 

Intestine,  large,  .         .   5  to  6 

small,       .         .     20     - 

Ligament,  round,  of  uterus    -     44 


ft.    in. 

-  6 

-  H 

-  2!- 

-  4 

3 
1 

l£ 

2 
f 

H 

2 
If 

li 


Ligameiit  of  ovary, 
Meatus  auditorius  externus 
Medulla  oblongata, 
Oesophagus,     . 
Pancreas,    . 
Pharynx, 
Rectum, 
Spinal  Cord,    . 
Tubulus  seminiferus,  . 
Urethra,  male, 

il        female, 
Ureter,    .... 
Vagina,        .         .         .   4  to 
Vas  deferens,  . 
Vesicula  seminalis, 

"  "  unravelled,  4  to 

Vocal  cord, 


n 

7 


-     3 


ft. 

in. 

n 
H 
ii 

10 

.  - 

7 

- 

44 

.  - 

8 

1 

5 

.    2 

o 

O 

_ 

O 
1; 

1 

4 

o  - 

G 

2 

_ 

.   - 

2 

to- 

G 

- 

i 

2 

APPENDIX. 


755 


SIZES   OF  VARIOUS   HISTOLOGICAL  ELEMENTS   AND 

TISSUES. 


Average  size  infractions  of  a  a  inch. 


Air-cells,  7V  to  -g^. 
Blood-cells  (red),  ,.,1(M1  (breadth). 
"Wens    (thickness), 
(colorless),  T^w. 


Canaliculus  of  bone. 


(width). 


Capillary  blood-vessels,  -^V,,-  (lung) 

to  T^1(T|7  (bone). 
Cartilage-cells  (nuclei  of),  3,,',,   . 
Chyle-molecules,  3Fo-jnr' 
Cilia,  ^  to  ^^  (length). 
Cones  of   retina   (at  yellow  spot), 

Tfimr  to  mho  (width). 
Connective-tissue  fibrils,  -rr.V,nr  to 

TTko  (width). 
Dentine-tubules,  ¥-gVo  (width). 
Enamel-fibres,  ^J^ff  (width). 
End-bulbs,  ^-J-g-. 
Epithelium 
columnar        (intestine),       ^,in 

(length). 
spheroidal  (hepatic),  -^jht  to  s;,„. 
squamous    (peritoneum),    ±  ^  0  6 

(width), 
squamous  (mouth), 
(skin), 
Elastic  (yel.)  fibres, 

(wide). 
Fat  cells,  -^  to  _ 
Germinal  vesicle, 

"  spot, 

Glands 
gastric,  ^  to  ,,\  (length). 

.  "       lh  to  ^  (width). 
Lieberkulm's  (small  intestines), 

t£o  to  B}T  (length). 
Lieberkuhn's    (small    intestine), 

^  (width). 
Pcyer's  (follicles),  fa  to  ,',. 
Sweat,  TjJjj  (width). 
"       in  axilla,  -fa  to  £  (width). 
Haversian     canals,     toutt    to 
(width). 


y  (width). 


"l 

•.'  4 i 


to 


To  o  o 


_1_ 

To  n- 

l 

3  0  0  U ' 


|  Lacunae  (bone),  y^Vff  (length). 
iA,  (width). 
Macula  Intra,  ^. 
Malpighian  bodies  (kidney),  yi^. 
"  corpuscles  (spleen),  ^(T 

to  J,, 
Muscle     (striated),     Tol7.  to     -^ 

(width). 
Muscle-cell    (plain),    r,1l7r    to     ..,',„ 
■       (length). 

Muscle-cell   (plain),    ^Vo  to 
I      (width). 

1  Nerve-corpuscles    (brain),  ^fa^  to 
.  i 

!         :i  o  o  • 

;  Nerve-fibres  (medullated),  12^6(>  to 
-y-gVrr  (width). 
Nerve-fibres  (non-medullatecl),s,,1nT, 
to  ^^  (width). 
1  Ovum,  jfo. 
Pacinian  bodies,  -j1T  to  ^  (length). 

"       A  to  -J,,  (width). 
Papillae  of  skhi  (palm).  £,',,l  to  ,,',,, 
(length). 
"       "    (face),  ,Uto?-U. 
"       tongue  (circumvallate),  2V 

to  ,V  (width).  " 
"       '•  (fungiform),  ^  to 

fa  (width). 
"       "       (filiform),/,,  (length). 
Pigment  cells  of  choroid  (hexago- 
nal),  n' 

Pigment-granules,  ?0-foo-. 
Spermatazoon,  ,-;,', ,r  to  -*,V(T  (length). 
head)TX*  (length). 
"    Too-iTo  (width). 

Touch-corpuscles,  -.,,',,,  (length). 
Tubuli     seminiferi.     -, ',  j     to     ,,',„ 

(width). 
Tubuli  uriniferi,  ,.  $  „. 
Villi,  J,  to  &  (length). 

"    ih  to  A-  (width). 


756 


APPENDIX. 


METEICAL    SYSTEM    OF    WEIGHTS    AND    MEASUEES 
COMPAEED   WITH  THE   COMMON  MEASUEES. 


Metre 

Centimetre 

Millimetre 


39f  inches  (about), 
-f  inch  (nearly). 
¥V  inch  (nearly) 


Gramme  =  15-J  grains  (nearly). 

Centigramme  =    ^\  grain  (about). 

Milligramme   =  -^  grain  (about). 


Litre     =     about  If  pints  (35^  oz.). 


CLASSIFICATION   OF    THE  ANIMAL   KINGDOM. 


Mammalia. 

Monodelphia. 

Primates, 

Cheiroptera, 

Insectivora, 

Carnivora,  . 

Proboscidea, 

Hyracoidea, 

Ungulata, 

Sirenia, 

Cetacea, 

Eodentia,    . 

Edentata, 

Didelphia, 

Ornithodelphia, 

Ayes. 

Carinatae, 
Ratitae, 

Eeptilia. 

Crocodilia,       . 
Ophidia, 
Chelonia, 
Lacertilia,   . 


Amphibia. 
Anura, 
Urodela, 


A.— VERTEBRATA. 

Typical  Examples. 

Man,  ape. 
.     Bat. 

Hedgehog. 
.     Cat,  dog,  bear. 

Elephant. 

Hyrax. 

Horse,  sheep,  pig. 
.     Dugong. 

Whale. 
.     Eabbit,  rat. 

Armadillo. 
.     Kangaroo. 

Duck-billed  platypus. 


Fowl,  duck. 
Ostrich. 


Crocodile. 
Snake. 
Tortoise. 
Lizard. 


Frog. 

Newt. 


Pisces, Lamprey,  shark,  cod. 


B.— INVERTEBRATA. 


MOLLUSCA. 

Odontophora, 
Lamellibranchiata, 
Brachiopoda, 
Polyzoa,   . 


Whelk,  snail. 
Mussel,  oyster. 
Terebratula. 
Sea  mat. 


APPENDIX. 


757 


Arthropoda. 
Crustacea,   . 
Arachnida, 
Insecta, 
Myriapoda, 

echinodermata, 

Vermes. 

Annelida, 

Platyhelminthes, 

Nemathelminthes, 

C<ELENTERATA. 

Actinozoa,    . 
Hydrozoa, 

Protozoa,    . 


Lobster. 

Scorpion,  spider. 
Bee,  fly. 
Centipede. 

Sea  stars. 


Earthworm. 
Tapeworm,  fluke. 
Round-worm,  thread-worm. 

Sea  anemone. 
Hydra. 

Amoeba,  Vorticella. 


INDEX. 


A. 

Abdominal  muscles,  action  of,  in  respira- 
tion, 182 
Aberration, 

chromatic,  603 

spherical,  602 
Abomasum,  246 
Absorbents.    See  Lymphatics. 
Absorption,  298 

by  blood-vessels,  311     ■ 

by  lacteal  vessels,  309 

by  lymphatics,  310 

conditions  for,  314 

by  the  skin,  3-52 

process  of  osmosis,  352 

rapidity  of,  313 

See  Chyle,  Lymph,   Lymphatics,  Lac- 
teals. 
Accelerator  centre,  498 
Accidental  elements  in  human  body,  753 
Accommodation  of  eye,  592 
Acids,  organic,  750 

acetic,  750 
in  gastric  juice,  252 
Acid-albumin.  252,  736 
Acini  of  secreting  glands,  330 
Actinic  rays,  614 
Addison's  disease,  392 
Adenoid  tissue,  35 
Adipose  tissue,  37.     See  Fat. 

development,  39 

situations  of,  37 

structure  of,  37 
Adrenals,  390 
After-birth,  678 
After-sensations, 

taste,  562 

touch,  555 

vision,  606 
Aggregate  glands,  330 
Agminate  glands,  263 
Air, 

atmospheric,  composition  of,  187 

breathing,  184 

complement  al,  184 

reserve,  184 

residual,  184 

tidal,  184 

changes  by  breathing,  188 


Air — continued. 

quantity  breathed,  184 

transmission    of    sonorous    vibrations 
through,  575 

in  tympanum,  for  hearing,  577  et  -seq. 

undulations  of,  conducted  by  external 
ear,  575 
Air-cells,  175 

Air-tubes,  170.     See  Bronchi. 
Albumin,  735 

acid,  252,  736 

action  of  gastric  fluid  on,  252 

alkali,  736 
characters  of,  734 

chemical  composition  of,  733 

derived,  736 

egg,  735 

native,  735 

serum,  79 

tissues  and  secretions  in  which  it  exists, 
735 

of  blood,  79 
Albuminoids,  733 
Albuminous  substances,  733 

absorption  of,  291 

action  of  gastric  fluid  on,  252 
of  liver  on,  286 
of  pancreas  on,  272 
Alcoholic  drinks,   effect    on    respiratory 

changes,  189 
Alimentary  canal,  241,  296 

development  of,  703 
Alkali-albumin,  736 
Allantoin,  370,  744 
Allantois,  671 
Alloxan,  368 
Aluminium,  753 
Ammonia, 

cyanate  of,  isomeric  with  urea,  365,  743 

exhaled  from  lungs,  191 

urate  of,  367 
Amnion,  669,  670 

fluid  of,  671 
Amoeba,  4 
Amoeboid  movements,  75 

cells,  4 

colorless  corpuscles,  75 

cornea-cells,  687 

protoplasm,  I 
Tradesc-antia.  5 


760 


INDEX. 


Amphioxus,  679 

Ampulla,  571 

Amyloids  or  Starches,  748 

action  of  pancreas  and  intestinal  glands, 
272,  290 
of  saliva  on,  235 
Amylopsin,  273,  746 
Amyloses,  748 
Anabolic  nerves,  632 
Anacrotic  wave,  141 

Anastomoses  of  muscular  fibres  of  heart, 
102 

of  nerves,  454 

of  veins,  157 

in  erectile  tissues,  163 
Anelectrotonus,  430 
Angle,  optical,  611 
Angulus  opticus  seu  visorius,  611 
Animal  heat,  316.     See  Heat  and  Temper- 
ature. 
Animals,  distinctive  characters,  10 
Antialbumose,  272 
Antihelix,  568 
Antipeptone,  272 
Antitragus,  568 
Anus,  295 
Aorta,  105 

development,  690 

pressure  of  blood  in,  146 

valves  of,  104 
action  of,  118 
Aphasia,  519 
Apnoea,  204 

Appendices  epiploicae,  267 
Appendix  vermiformis,  266 
Aquseductus, 

cochleae,  572 

vestibuli,  571 
Aqueous  humor,  594 
Arachnoid,  472 
Arches,  visceral,  681 
Area  germinativa,  661 

opaca,  661 

pellucida,  661 

vasculosa,  669 
Areolar  tissue,  34 
Arsenic,  753 
Arterial  tension,  143 
Arteries,  105 

circulation  in,  134 
velocity  of,  159 

distribution,  105 

muscular  contraction  of,  136 

effect  of  cold  on,  137 

effect  of  division,  137 

elasticity,  134 
purposes  of,  135 

muscularity,  136 

governed  by  nervous  system,  147 
purposes  of,  136 

nerves  of,  147 

nervous  system,  influence  of,  147 

office  of,  147 

pressure  of  blood  in,  143 

pulse,  137.     See  Pulse. 


Arteries — continued. 

rhythmic  contraction,  136  et  seq. 

structure,  105  et  seq. 
distinctions  in  large  and  small  arteries, 
105 

systemic,  105 

tone  of,  148 

umbilical,  696 

velocity  of  blood  in,  159 
Articulate  sounds,  classification  of,  447 

See  Vowels  and  Consonants. 
Arytenoid  cartilages,  439 

effect  of  approximation,  440 
movements  of,  440 

muscle,  439 
Asphyxia,  204 

causes  of  death  in,  206 

experiments  on,  207 

symptoms,  205 
Astigmatism,  602 
Atmospheric  air,  187.     See  Air.  _ 

pressure  in  relation  to  respiration,  178 
Auditory  canal,  568  et  seq. 

function,  567 
Auditory  centre,  529 
Auditory  nerve,  574 

distribution,  574 

effects  of  irritation  of,  584 

pits,  669 
Auerbach's  plexus,  260 
Auricles  of  heart,  97,  100 

action,  115 

capacity,  100 

development,  687 

dilatation,  128 

force  of  contraction,  128 
Automatic  action,  470 

cerebrum,  514 

medulla  oblongata,  496  et  seq. 

respiratory,  497 
Axis-cylinder  of  nerve-fibre,  452 


Bacterium  lactis,  339 
Baritone  voice,  444 
Basement-membrane, 

of  mucous  membranes,  329 

of  secreting  membranes,  325 
Bass  voice,  444 
Battery,  Daniell's,  408 
Benzoic  acid,  368,  751 
Bicuspid  valve,  100 
Bidder's  ganglia,  130 
Bile,  279 

antiseptic  power,  286 

coloring  matter,  280 

composition  of,  279 

digestive  properties,  285 

excrementitious,  283 

fat  made  capable  of  absorption  by,  285 

functions  in  digestion,  283 

mixture  with  chyme,  285 

mucus  in,  281 


INDEX. 


761 


Bile — continued. 
natural  purgative,  286 
process  of  secretion,  282 
quantity,  283 
re-absorption,  284 
salts,  279 

secretion  and  flow,  282 
secretion  in  fcetus,  2*4 
tests  for,  280,  281 
uses,  283 
Bilifulvin,  Biliprasiu,  Bilirubin,  Biliver- 

diu,  280,  745 
Biliii,  279 
preparation  of,  279 
re-absorption  of,  -s4 
Bioplasm,  2.     See  Protoplasm. 
Bladder,  urinary,  360.     See  Urinary  Blad- 
der. 
Blastema.     See  Protoplasm. 
Blastodermic  membrane,  659 
Bleeding,  effects  of,  on  blood,  90 
Blind  spot,  604 
Blood,  57 
albumin,  78 
arterial  and  venous,  90 
buffy  coat,  60 
chemical  composition,  77 
coagulation,  58  et  seq. 
color,  57 

changed  by  respiration,  193 
coloring  matter,  86  et  *  q. 
coloring  matter,  relation  to  that  of  bile, 

281 
composition,  chemical,  77 

variations  in,  89 
corpuscles  or  cells  of,  70.     See  Blood- 
corpuscles, 
red,  70 
white,  74 
crystals,  84 
cupped  clot,  60 
development,  91 
extractive  matters,  79 
fatty  matters,  79 
fibrin,  60 

separation  of,  60 
formation  in  liver,  92 

in  spleen,  385 
gases  of,  81 
haemoglobin,  83 
hepatic,  91 
menstrual,  648 
odor  or  halitus  of,  57 
portal,  characters  of,  91 

purification  of,  by  liver,  285 
quantity,  57 
reaction,  57 

relation  of,  to  lymph,  309 
saline  constituents,  80 
serum  of,  78 

compared    with    secretion  of  serous 
membrane,  309 
specific  gravity,  57 
splenic,  91 
structural  composition,  70 


Blood — continued. 
temperature,  57 
uses,  94 
of  various  constituents.  94 

variations  of ,  in  different  circumstances, 
89 
in  different  parts  of  body,  90 
Blood-corpuscles,  red.  To 

action  of  reagents  on.  71 

chemical  composition,  80 

development,  92,  686 

disintegration  and  removal,  386 

method  of  counting,  76 

rouleaux,  71 

sinking  of,  60 

specific  gravity,  71 

stroma,  70 

tendency  to  adhere,  71 

varieties,  71 

vertebrate,  various,  72 
Blood-corpuscles,  white,  74 

amoeboid  movements  of,  75 

derivation  of,  93 

formation  of,  in  spleen,  94,  385 

locomotion,  75 
Blood-crystals,  84 
Blood-pressure,  143 

influence  of  vaso-motor  system  of,  147 

variations,  147 
Blood-vessels, 

absorption  by,  311 
circumstances  influencing,  o  1-4 
difference  from  lymphatic  absorption, 

310  et  seq. 
osmotic  character  of,  311 
rapidity  of,  313 

development,  686 

influence  of  nervous  system  on,  149 
Bone,  44 

canaliculi,  46 

cancellous,  44 

chemical  composition,  44 

compact,  44 

development,  49  et  seq. 

functions,  56 

growth,  56 

Haversian  canals,  46 

lacunie,  46 

lamellae,  48 

marrow,   44 

medullary  canal,  44 

periosteum,  45 

structure,  44 
Branchial  clefts,  681 
Brain.     See  Cerebellum,  Cerebrum,  Pons, 
etc. 

adult,  509 

amphibia,  509 

apes,  510 

birds,  509 

capillaries  of,  162 

child,  509 

circulation  of  blood  in,  162 

convolutions,  503 

development,  697 


762 


INDEX. 


Brain,  continued. 

female,  509 

fish,  509 

gorilla,  510 

idiots,  509 

lobes,  503 

male,  509 

mammalia,  509 

orang,  511 

proportion  of  water  in,  752 

quantity  of  blood  in,  163 

rabbit,  509 

reptiles,  509 

"weight,  509 
relative,  509 
Breathing,  167.    See  Respiration. 
Breathing  air,  184 
Bronchi,   arrangement  and  structure  of, 

170 
Bronchial  arteries  and  veins,  177 
Brunner's  glands,  263 
Buffy  coat,  formation  of,  60 
Bulbus  arteriosus,  690 
Burdach's  column,  479 
Burs*  mucosae,  326 
Butyric  acid,  252 

C. 

Caecum,  266 

Calcification  compared  with  ossification, 

55 
Calcium,  732 

fluoride,  753 

phosphate,  753 

carbonate,  753 
Calculi,    biliary,    containing  cholesterin, 

747 
Calyces  of  the  kidney,  353 
Canal,  alimentary.     See  Stomach,   Intes- 
tine, etc. 

external  auditory,  568 
function  of,  575 

spiral,  of  cochlea,  572 
Canaliculi  of  bone,  46 
Canalis  membranaceus,  572 
Canals,  Haversian,  46 

portal,  275 

semicircular,  571 

function  of,  580 
Cancellous  texture  of  bone,  44 
Capacity  of  chest,  vital,  184 

of  heart,  100 
Capillaries,  109 

circulation  in,  153 
rate  of,  160 

contraction  of,  156 

development,  686 

diameter  of,  110 

influence  of,  on  circulation,  156 

lymphatic,  300 

network  of,  110 

number,  112 

passage  of  corpuscles  through  walls  of, 
154 


Capillaries — continued. 

pressure  in,  156 

resistance  to  flow  of  blood  in,  155 

still  layer  in,  153 

structure  of,  109 

of  lungs,  177 

of  stomach,  250 
Capsule,  external,  521 

internal,  520 

of  Glisson,  .75 
Capsules,  Malpighian,  357 
Carbon,  732 
Carbonic  acid  in  atmosphere,  187 

in  blood,  89 

effect  of,  199 

exhaled  from  skin,  351 

increase  of,  in  breathed  air,  188 

in  lungs,  192 

in  relation  to  heat  of  body,  319 
Carbonates,  753 
Cardiac  orifice  of  stomach,  action  of,  258 

sphincter  of,  258 
relaxation  in  vomiting,  258 
Cardiac  revolution,  121 
Cardiograph,  124 
Cardio-inhibitory  centre,  497 
Carnivorous  animals,  food  of,  246 

sense  of  smell  in,  566 
Carotid  gland,  393 
Cartilage,  40 

articular,  41 

cellular,  41 

chondrin  obtained  from,  43 

classification,  40 

development,  44 

elastic,  42 

fibrous,  42.     See  Fibro-cartilage. 

hyaline,  40 

matrix,  40 

ossification,  51 

perichondrium  of,  52 

structure,  41 

temporary,  41 

uses,  43 

varieties,  40 
Cartilage  of  external  ear,  used  in  hearing, 

575 
Cartilages  of  larynx,  439 
Casein,  736.     See  Milk. 
Cauda  equina,  472 
Caudate  ganglion  corpuscles,  455 

nucleus,  521 
Cause  of  fluidity  of  living  blood,  67 
Cells,  2 

abrasion,  10 

amoeboid,  4 

blood,  70.     See  Blood-corpuscles. 

cartilage,  40 

chemical  transformation,  10 

ciliated,  25 

classification,  15 

decay  and  death,  9 

definition  of,  2 

epithelium,  19.     See  Epithelium. 

fission,  7,  9 


INDEX. 


,(•>:; 


Cells — continued. 
formative,  661 
functions,  4  et  seq. 
gemmations,  7,  9 
gustatory,  560 
lacunar  of  bone,  47 
modes  of  connection,  17 
nutrition,  5 
olfactory,  565 
pigment,  20 
reproduction,  7 
segmentation,  12 
structure,  17  et  seq. 
transformation,  9 
varieties,  15 
vegetable,  11 
distinctions  from  animal  cells,  11 
Cellular  cartilage,  41 
Cement  of  teeth,  229 
Centres,  nervous,  etc.     See  Nerve-centres. 

of  ossification,  55 
Centrifugal  nerve-fibres,  458 
Centripetal  nerve-fibres,  458 
Cerebellum,  524 
co-ordinating  function  of,  527 
cross-action  of,  528 
effects  of  injury  of  crura,  528 

of  removal  of,  527 
functions  of,  525 
in  relatiou  to  sensation,  526 
to  motion,  527 
to  muscular  sense,  528 
structure  of,  525 
Cerebral  circulation,  162 

hemispheres,  502.     See  Cerebrum. 
Cerebral  nerves,  530 
third,  531 

effects  of  irritation  and  injury  of,  531 
relation  of,  to  iris,  532 
fourth,  533 
fifth,  533 
distribution  of,  533 
effect  of  division  of,  534 
influence  of, 

on      muscles      of     mastication, 

534 
on  organs  of  special  sense,  537  et 

8t '/. 

relation  of,  to  nutrition,  536 
resemblance  to  spinal  nerves,  533 
sensory  function  of  greater  division  of 

fifth*.  534 
sixth,  537 

communication  of,  with  sympathetic, 
537 
seventh,  538.     See  Facial  Nerve. 
ninth,  539 
tenth,  540 
eleventh,  544 
twelfth,  545 

Cerebration,  unconscious,  514 

Cerebrin,  743 

Cerebro-cerebellar  fibres,  523 

Cerebrospinal  fluid,   relation  to  circula- 
tion, 163 


Cerebro-spinal  nervous  system,  472  it  seq 

See  Brain,  Spinal  Cord,  etc. 
Cerebrum,  its  structure,  508 

chemical  composition,  509 

convolutions  of,  503  et  seq. 

crura  of,  499 

development,  697 

distinctive  character  in  man,  510 

effects  of  injury,  512 

removal,  512 

electrical  stimulation,  516 

functions  of,  511 

gray  matter,  508 

in  relation  to  speech,  519 

in  relation  to  other  parts,  502 

localization  of  functions,  513 

structure,  508  et  a  q. 

unilateral  action  of,  512 

white  matter,  508 
Cerumen,  or  ear-wax,  345 
Characteristics  of    organic    compounds, 

733 
Chemical  composition  of  the  human  body, 

732 
Chest,  its  capacity,  184 

contraction  of,  in  expiration,  1S2 

enlargement  of,  in  inspiration,  179 
Chest-notes,  445 
Cheyne-Stokes1  breathing,  204 
Chlorine,  7:52 

in  human  body,  732 

in  urine,  372 
Cholesterin,  747 

in  bile,  281 
Choletelin,  369,  745 
Chondrin,  741 
Chorda  dorsalis,  663 
Chorda  tympani,  238  it  seq. 
Chorda-  tendinese,  103 

action  of,  118 
Chorion, 

false,  671 

true,  672 

villi  of,  673 
Choroid  coat  of  eye,  587 

blood-vessels,  587 
Choroidal  fissure,  700 
Chromatic  aberration,  608 
Chyle,  308 

absorption  of,  309 

analysis  of,  309 

coagulation  of,  309 

compared  with  lymph,  308 

corpuscles  of,  309.     >"  Chyle-corpus- 
cles. 

fibrin  of,  309 

forces  propelling,  303 

molecular  base  of    308 

quantity  found,  309 

relation  of,  to  blood,  309 
Chyle-corpuscles,  309 
Chyme,  252 

absorption  of  digested  parts  of,  291 

changes  of  in  intestine,  291  etseq. 
Cilia.  25 


764 


INDEX. 


Ciliaiy  epithelium,  25 

function  of,  25 
Ciliary  motion,  25 

nature  of,  25 
Ciliary-muscles,  596 

action  of  in  adaptation  to  distances,  598 
Ciliary  processes,  591 
Circulation  of  blood,  95 

action  of  heart,  115 

agents  concerned  in,  165 

arteries,  184 

brain,  162 

capillaries,  153 

course  of,  95  et  seq. 

discovery,  165 

erectile  structures,  163 

total,  694 

forces  acting  in,  165 

influence  of  respiration  on,  200 

peculiarities  of,  in  different  parts,  162 

portal,  275 

proofs,  155 

pulmonary,  193 

systemic,  95 

in  veins,  156 
velocity  of,  158 
Circumvallate  papillae,  558 
Claustrum,  521 
Claviculi  of  Gagliardi,  49 
Clefts,  visceral,  681 
Clitoris,  640 

development  of,  712 
Cloaca,  711 

Clot  or  coagulum  of  blood    58 
See  Coagulation. 

of  chyle,  309 
Coagulation  of  blood,  58 
absent  or  retarded,  66 
conditions  affecting,  66 
theories  of,  67 

of  chyle,  309 

of  lymph,  309 
Coat,  bully,  60 
Coats  of  arteries,  106 
Coccygeal  gland,  393 
Cochlea  of  the  ear,  571 

office  of,  580 
•Cohnheim's  fields,  397 
Cold-blooded  animals,  318 

extent  of  reflex  movements  in,  485 

retention  of  muscular  irritability  in,  410 
Colloids,  313 
Colon,  266 
Colostrum,  338 
Color-blindness,  617 
■Coloring  matter, 

of  bile,  280 

of  blood,  83 

of  urine,  368 
Colors,  optical  phenomena  of,  614  et  seq. 
Columnar  carnea;,  103 
Columnar  epithelium,  23 
Complemental  air,  184 

colors,  614  et  seq. 
Compounds,  732 


Compounds — continued. 

inorganic,  751 

organic,  733 
Concha,  568 

use  of,  575 
Conducting  paths  in  cord,  482 
Cones  of  retina,  589 
Coni  vasculosi,  641 
Conjunctiva,  584 
Connective  tissues,  29 

classification,  29 

corpuscles  of,  30 

fibrous,  32 

gelatinous,  35 

retiform,  35 

varieties,  29 
Consonants,  447 

varieties  of,  447 
Contralto  voice,  444 
Control  centres,  498 
Convolutions,  cerebral,  503  et  seq. 
Co-ordination    of  movements,    office  of 

cerebellum  in,  527 
Copper,    an    accidental    element    in  the 

body,  753 
Cord,  spinal.     See  Spinal  Cord. 

umbilical,  678 
Cords,  tendinous,  in  heart,  103 

vocal.     See  Vocal  Cords. 
Corium,  342 
Cornea,  586 

corpuscles,  586 

nerves,  587 

structure,  586 
Corpora  Arantii,  104 

geniculata,  500 

quadrigemina,  500 
their  function,  500 

striata,  521 
their  function,  523 
Corpus  callosum,  503 

cavernosum  penis,  163 

dentatum 
of  cerebellum,  525 
of  olivary  body,  495 

luteum,  649 

of  human  female,  650 
of  mammalian  animals,  650 
of  menstruation  and  pregnancy  com- 
pared, 652 

spongiosum  urethra? ,  163 
Corpuscles  of  blood,  70.     See  Blood-cor- 
puscles. 

of  connective  tissue,  30 

Zimmerman,  388 
Correlation  of  life  with  other  forces,  713 
Cortical  substance  of  kidney,  353 

of  lymphatic  glands,  306 
Corti's  rods,  572 

office  of,  581 
Costal  types  of  respiration,  181 
Coughing,    influence   on    circulation    in 
veins,  102 

mechanism  of,  195 
Cowper's  glands,  644 


INDKX. 


765- 


Cranial  nerves.     See  Cerebral  nerves. 
Cranium,  development  of,  678 
Crassamentum,  59 
( Irescents  of  Gianuzzi.     See  Semilunes  of 

Heidenhain. 
Crico-arytenoid  muscles,  439 
Cricoid  cartilages,  439 
Crossed  pyramidal  tract,  479 

paralysis,  499 
Crura  cerebelli, 

effect  of  dividing.  527  et  seq. 
of  irritating,  527 

cerebri,  499 
their  office,  500 
Crusta,  499 
Crusta  petrosa,  226 
Crystallin,  737 
Crystalline  lens,  591 

in  relation  to  vision  at  different  dis- 
tances. 597 
Crystalloids,  313 

blood.  84  et  seq. 
Cubic  feet  of  air  for  rooms.  200 
Cupped  appearance  of  blood  clot,  60 
Curdling  ferments,  273 
Currents  of  action,  427 

ascending,  429 

continuous,  407 

descending.  429 

induced,  408 

muscle,  405 

natural,  405 

negative  variation,  427 

nerve,  428 

polarizing,  429 

rest,  427 
Curves,  Traube-Hering's,  204 
Cuticle.     See  Epidermis,  Epithelium. 

of  hair,  345 
Cutis  vera,  342 
Cystic  duct,  278 
Cystin  in  urine,  372 


D. 


Daltonism,  617 
Daniell's  batter}',  408 
Decidua, 

mensi  rualis,  648 

reflexa,  675 

serotina,  675 

vera,  675 
Decomposition,  tendency  of  animal  com- 
pounds to,  733 
Decomposition-products,  741 
Decussation  of  fibres  in   medulla  oblon- 
gata,  492,  493 
in  spinal  cord,  478 

of  optic  nerves,  529 
Defsecation,  mechanism  of,  295 

influence  of  spinal  cord  on,  188 
Deglutition,  244.     Set  Swallowing. 
Dentine,  224 
Depressor  nerve,  149 


Derived-albumins,  736 
Derma.  342 

Descendens  noni  nerve,  545 
Descemet's  membrane,  587 
Development,  656 
of  organs,  678 

alimentary  canal,  703 

arteries,  690 

blood,  91  et  seq. 

blood-vessels,  686 

bone,  49 

brain,  697 

capillaries,  686 

cranium,  678 

ear,  702 

embryo,  656 

extremities,  683 

eye,  700 

face  and  visceral  arches.  681 

heart,  685 

liver,  693,  705 

lungs,  706 

medulla  oblongata,  697 

muscle.  398,  401 

nerves.  696 

nervous  system,  696 

nose,  703 

organs  of  sense,  700 

pancreas.  705 

pituitary  body,  680 

respiratory  apparatus,  706 

salivary  glands,  705 

spinal  cord,  696 

teeth,  226 

vascular  system,  684 

veins,  692 

vertebral  column  and  cranium,  67S 

visceral  arches  and  clefts,  681 

of  Wolffian  bodies,  urinary  apparatus 
and  sexual  organs,  706 
Dextrin,  749 
Diabetes,  289 

Diapedesis  of  blood-corpuscles,  1 54 
Diaphragm, 

action  of,  on  abdominal  viscera,  182 
in  inspiration,  179 
in  various  respiratory  acts,  182 
in  vomiting.  258 
Diastase  of  liver,  288 
Diastole  of  heart.  115 
Dicrotous  pulse,  141 
Diet- 
daily,  219 

mixed,  necessity  of,  210  et  seq. 
Diffusion  of  gases  in  respiration.  192 
Digestion,  220 

in  the  intestines,  290  et  seq. 

in  the  stomach.  250 

influence  of  nervous  system  on,  294 

of  Stomach  after  death,  257 

Set  Gastric  tin  it  I.  Food,  Stomach. 

Dilatation  of  pupil,  491 

Diplopia,  620 

Direct  cerebellar  trad,  it'.i 
pyramidal  trad,   I  !!• 


166 


IXDEX. 


Direction  of  sounds,  perception  of,  582 

Discus  proligerus,  636 

Disdiaclasts,  397 

Distance,  adaptation  of  eye  to,  596 

of  sounds,  how  judged  of,  583 
Distinctness  of  vision,  how  secured,  600 

et  seq. 
Divisions  of  functions,  12 
Dorsal  laminae,  664 
Double  hearing,  583 

vision,  620 
Dreams,  515 

Drowning,  cause  of  death  in,  207 
Ductless  glands,  383 
Ducts  of  Cuvier,  693 
Ductus  arteriosus,  691 

venosus,  693 

closure  of,  692 
Duodenum.  260 
Duration  of  impressions  on  retina,  605 

intestinal  digestion,  294 
Duverney's  glands,  640 
Dyspnoea,  204 


E. 


Ear,  567 

bones  or  ossicles  of,  569 

function  of,  578 
development  of,  702 
external,  568 

function  of,  575 
internal,  570 

function  of,  579 
middle,  568 

function  of,  576 
Ectopia  vesica;,  381 
Efferent  nerve  fibres,  458 
vessels  of  kidney,  358 
Egg-albumin,  735 
Elastic  cartilage,  42 
fibres,  31 
tissue,  33 
Elastin,  32,  741 
Elastic  after  vibration,  412 
Electricity, 
in  muscle,  405 
nerve,  427 
retina,  609 
Electrodes,  404 
Electrotonus,  429 

Elementary    substances    in    the    human 
body,  732 
accidental,  753 
Embryo,  656  et  neq.     See  Development. 
Embryonic  shield,  661 
Emmetropic  eye,  600 
Emotions,    connection  of,  with    cerebral 

hemispheres,  511 
Emulsifi cation,  273 
Enamel  of  teeth,  225 
Enamel  organ,  226 
End-bulbs,  463 
End-plates,  motorial,  400 


Endocardium,  102 
Endolymph,  570 

function  of,  579 
Endomysium,  396 
Endoneurium,  554 
Endosmometer,  311 
Endothelium,  20 
distinctive  characters,  20 
germinating,  21 
Energy, 

relations  of  vital    to    physical,    chap, 
xxiv. 

daily  amount  expended  in  body,  433 
Epencephalon,  699 
Epiblast,  13,  661 
Epidermis,  340 

functions  of,  348 

pigment  of,  341 

structure  of,  340 
Epididymis,  640 
Epiglottis,  168 

structure,  168 
Epineurium,  453 
Epithelium,  19 

air-cells,  175 

arteries,  108 

bronchi,  172 

bronchial  tubes,  172 

ciliated,  25 

cogged,  28 

columnar,  23 

cylindrical,  23 

functions,  28 

glandular,  23 

goblet-shaped,  24 

mucous  membranes.  329 

olfactory  region,  565 

secreting  glands,  333 

serous  membranes,  326 

spheroidal,  23 

squamous  or  tesselated,  20 

stratified,  27 

transitional,  26 
Erect  position  of  objects,  perception  of, 

609 
Erectile  structures,  circulation  in,  163 
Erection,  163 

cause  of,  163 

influence  of  muscular  tissue  in,  164 

a  reflex  act,  489 
Ery thro-granulose ,  235 
Erythro-dextrin,  235 
Eunuchs,  voice  of,  445 
Eustachian  tube,  568 

development,  702 

function  of,  579 
Eustachian  valve.  97,  689,  695 
Excreta  in  relation  to   muscular  action, 

432  etseg. 
Excretin,  747 
Excretion,  325 
Exercise, 

effects  of,  on   production   of   carbonic 
acid,  189 
on  temperature  of  body,  :>17 


INDEX. 


tg: 


Expenditure  of  body,  432  et  seq. 
Expiration,  182 

influence  of,  on  circulation,  202 

mechanism  of,  183 

muscles  concerned  in,  1S8 

relative  duration  of,  183 
Expired  air,  properties  of,  188  <  t  seq. 
Extractive  matters, 

in  Mood,  T'.t 

in  urine,  381 
Extremities,  development  of,  683 
Eye,  585 

adaptation  of  vision  at   different   dis- 
tances, 590  et  seq. 

blood-vessels,  591 

development  of,  700 

optical  apparatus  of.  592 

refracting-  media  of.  598 

resemblance  to  camera,  592 
Eyelids,  5S4 

development  of,  702 
Eyes,    simultaneous  action  of,    in  vision, 
622 


P. 


Eace,  development  of.  681 
Facial  nerve,  538 

effects  of  paralysis  of,  538 

relation  of,  to  expression,  538 
Faeces,  composition  of,  295 

quantity  of.  295 
Fallopian  tubes,  038 

opening  into  abdomen,  038 
Falsetto  notes.  440 
Fasciculus, 

cuneatus,  494 

muscle,  396 

olivary,  493 

teres,  493 
Fasting, 

influence  on  secretion  of  bile,  282 
Fat.     S,c  Adipose  tissue. 

action  of  bile  on,  285 
of  pancreatic  secretion,  278 
of  small  intestine  on,  291 

absorbed  by  lacteals,  80s 

formation  of,  435 

in  blood,  80 

in  relation  to  heat  of  body,  322 

of  bile.  281 

of  chyle,  309 

situations  where  found,  87 

uses  of,  39 
Fechner'slaw.  606 
Female  generative  organs,  634 
Fenestra  ovalis,  571 

rotunda,  571 
Ferments,  64,  745 
Fibres,  IS 

of  Midler,  590 
Fibrils  or  filaments,  Is 
Fibrin,  738,  in  blood,  50 

in  chyle,  308,  309 

formation  of,  60 


Fibrin — continued. 
in  lymph,  :;<is.  309 
sources  and  properties  of,  788 

vegetable.  212 
Fribrinogen.  08  .  /  seq.,  738 
Fibrinoplastin,  63  etseq. 
Fibro-cartilage,  42 
classification,  40 
development,  44 
white,  42 
yellow,  42 
Fibrous  tissue,  32 

white.  32 

yellow.  :',:;  , 

development,  36 
Fick's  kymograph,  144 
Field  of   vision,  actual   and    ideal  size  of 

611 
Fifth  nerve.     Set  Cerebral  Ner 
Fillet.  498 
Filtration,  313,  8;:'. 
Filum  terminate,  472 
Fimbriae  of  Fallopian  tube,  638 
Fingers,  development  of,  084 
Fish, 

temperature  of,  817 
Fissures, 

of  brain.  508  <  t  seq. 

of  spinal  cord.  474 
Fistula,  gastric,  experiments  in  cases  of, 

251 
Flesh,  of  animals,  2 10 
Fluids,  passage  of,   through  membranes 

311 
Fluoride  of  calcium,  75:'. 
Focal  distance,  596 
Foetus, 

blood  of,  91 

circulation  of,  694 

communication  with  mother,  070 

faeces  of.  283 

faeces  of,  office  of  bile  in.  283 

membranes,  669  >  t  seq. 

pulse  in,  126 
Folds,  head  and  tail,  667 
Follicles,  Graafian.      8et    Graafian   Vehi- 
cles. 
Food,  208 

albuminous,  changes  of,  252,  272 

amyloid,  changes  "of.  28,."),  272,  290 

classification  of,  209 

digestibility  of  articles  of,  210 

value  dependent  on,  210 

digestion  of,  in  intestines,  290  1 1  seq. 

in  stomach,  250  <  t  a  7. 

improper,  216 

of  man,  209 

mixed,  the  best  for  man,  210 

mixture  of,  necessary,  210 
too  little,  214 
too  much,  21 7 

vegetable,    contains  nitrogenous    prin- 
ciples 212 
Foot-pound,  138 

ion.  12s 


768 


INDEX. 


Foramen  ovale,  99,  695 

Forced  movements,  528 

Form  of  bodies,  how  estimated,  613 

Formation  of  fat,  435 

Formic  acid,  750 

Fornix,  505 

Fourth  cranial  nerve,  533 

ventricle,  492 
Fovea  centralis,  588 
Fundus  of  bladder,  360 
Fundus  of  uterus,  639 
Fungiform  papilla;  of  tongue,  559 
Funiculus  of  Rolando,  494 


a. 


Galactophorous  ducts,  336 
Gall-bladder,  278 

structure.  278 
Ganglia.     See  Nerve  centres. 
Ganglion,  Gasserian,  533 

corpuscles,  455 

See  Nerve-corpuscles. 
Gases,  732 

in  bile,  282 

in  blood,  81 

extraction  from  blood,  81 

in  stomach  and  intestines,  296 

in  urine,  373 
Gastric  glands,  248 
Gastric  juice.  250 

acid  in,  251 

action  of,  on  nitrogenous  food,  252 

on  non-nitrogenous  food,  253 

on    saccharine    and    amyloid    prin- 
ciples, 254 

characters  of.  250 

composition  of,  250 

digestive  power  of,  252 

experiments  with,  255 

pepsin  of,  252 

quantity  of,  251 

secretion  of,  251 
how  excited,  251 

influence  of  nervous  system  on,  256 
Gelatin,  740 

as  food,  217 

action  of  gastric  juice  on,  254 

action  of  pancreatic  juice  on,  272 
Gelatinous  subtances,  740 
Generation  and  development,  634 
Generative  organs  of  the  female,  634 

of  the  male,  640 
Gerlach's  network,  476 
Germinal  area,  661 

epithelium,  636 

matter,  2.     See  Protoplasm. 
Germinal  membrane,  659 

spot,  636 

vesicle,  636 
Gill,  167 

Gizzard,  action  of,  255 
Gland,  pineal,  392 

pituitary,  392 


Gland,  prostate,  644 

Gland-cells,  agents  of  secretion,  325 

changes  in  during  secretion,  249,  270,. 
339 
Gland-ducts,  arrangement  of,  333 

contractions  of,  333 
Glands,  aggregate,  330 

Brunner's,  262 

ceruminous,  345 

Cowper's,  644 

ductless,  383.    See  Vascular. 

Duverney's,  640 

of  large  intestine,  268 

of  Lieberkiihn,  262 

lymphatic,  305.  See  Lymphatic  Glands. 

mammary,  333 

of  Peyer,  262 

salivary,  239 

sebaceous,  345 

secreting,  329.    See  Secreting  Glands. 

of  small  intestines,  262 

of  stomach,  248 

sudoriferous,  344 

tubular,  330 

vascular,  383.    See  Vascular  Glands.. 

vulvo- vaginal,  640 
Glandula  Nabothi,  639 
Glisson's  capsule,  274 
Globulin,  78,  737 

distinctions  from  albumin,  79 
Globus  major  and  minor,  640 

development,  707 
Glossopharyngeal  nerve,  539 

communications  of,  539 

motor  filaments,  540 

a  nerve  of  common  sensation  and  of 
taste,  540 
Glottis,  action  of  laryngeal  muscles  on,  440 

closed  in  vomiting,  258  et  seq. 

forms  assumed  by,  441 

narrowing  of,  proportioned  to  height  of 
note,  443 

respiratory  movements  of,  183 
Glucose,  236,  748,  749 

in  liver,  288 

test  for,  236 
Gluten  in  vegetables,  212 
Glycerin,  273,  747 
Glycin,  742 
Glycocholic  acid,  279 
Glycogen,  286,  748 

characters,  288 

destination,  288 

preparation,  288 

quantity  formed,  287 

variation  with  diet,  287 
Glycosuria,  289 

artificial  production  of,  289 
Gmelin's  test,  281 
Goll's  column,  479 
Graafian  vesicles,  636 

formation  and  development  of,  637  et 
neq. 

relation  of  ovum  to,  637 

rupture  of,  changes  following,  649 


INDEX. 


:69 


Granular  layers  of  retina,  589 
Flogel,  398 
Grape-sugar.  See  Glucose. 
Gray  matter  of  cerebellum,  525 

of  cerebrum,  508 

of  crura  cerebri,  500 

of  medulla  oblongata,  495 

of  pons  Varolii,  499 

of  spinal  cord,  476 
Groove,  primitive,  662 
Growth,  6 

coincident  with  development,  6 

of  bone,  56 

not  peculiar  to  living  beings,  6 
Guanin,  744 
Gubernaculum  testis,  710 

II. 

Habitual  movements,  470 
Haematin,  86 

hydrochlorate  of,  88 
Hsemadynamometer,  144 
Haematochometer,  160 
Hsematoidin,  88 
Ha;matoporphyrin,  87 
Hsemin,  88 
Ha-mochromogcn,  87 
Hamiocytometer,  77 
Ihemoglobin,  83  et  seq. 
action  of  gases  on,  86 
derivatives  of,  86 
distribution   88 
estimation  of,  88 
spectrum,  84 
Hair-follicles,  346 

their  secretion,  349 
Hairs,  345 

chemical  composition  of,  741 
structure  of,  345 
Half  vision  centre,  529 
Hamulus,  572 
Harelip,  682 

Hassall,  concentric  corpuscles  of,  388 
Haversian  canals,  46 
Head-folds,  667 

Hearing,  anatomy  of  organ  of,  567 
double,  583 

impaired  by  lesion  of  facial  nerve,  538 
influence  of  external  ear  on,  575 
of  labyrinth,  579 
of  middle  ear,  576 
physiology  of,  575 
See  Sound,  Vibrations,  etc. 
Heart,  97  et  seq. 
action  of,  115 
accelerated,  133 
force  of,  126 
frequency  of,  126 
inhibited',  131 

inhibited  after  removal,  131 
rhythmic,  126  et  seq. 
work  of,  128 
auricles  <>f,  99,  100.     See  Auricles. 
49 


Heart — continued. 
capacity,  100 
chambers,  99 
chordae  tendinese  of,  103 
columme  carnese  of,  103 
course  of  blood  in,  115 
development,  687  , 

endocardium,  102 
force,  126 
frog's,  129 
ganglia  of,  128 
impulse  of,  123 

tracing  by  cardiograph,  124  et  seq. 
influence  of  pneumogastric  nerve,  131 

of  sympathetic  nerve,  133 
investing  sac,  97 
muscular  fibres  of,  102 
musculi  papillares,  104 
nervous  connections  with  other  organs, 
133 
rhythm,  126 
nervous  system,  influence  on,  128 
revolution  of,  121 
situation,  97 
sounds  of,  121 

causes,  122 
structure  of,  98 
tendinous  cords  of,  103 
tubercle  of  Lower  in,  99 
valves,  103 
arterial  or  semilunar,  104 

function  of.  118 
auriculo-ventricular,  103 
function  of,  117 
ventricles,  their  action,  116,  127 

capacity,  100 
weight  of,  100 
work  of,  128 
Heat,  animal.     See  Temperature, 
influence  of  nervous  system,  323 
of  various  circumstances  on,  316 
et  seq. 
losses  by  radiation,  etc.,  320 
sources  and  modes  of  production,  318 
developed    in   contraction  of  muscles, 
319 
Heat  centres,  323 
Heat-producing  tissues,  318 
Heat  or  rut,  646 

analogous  to  menstruation,  646 
Height,   relation  to  respiratory  capacity, 

185 
Helicotrema,  572 
Helix  of  ear.  568 
Helmholz's  modification,  410 
Hemipeptone,  272 

Hemispheres,    Cerebral,    508.     Set    Cere- 
brum. 
Benson's  disc.  398 

Hepatic  cells,  271 

duets,  277 

veins,  275 

vessels,  arrangement  of,  2~~>  ,t  seq. 
Herbivorous  animals, 

perception  of  odors  by,  566 


770 


INDEX. 


Hering's  theory,  615 

Hiccough,  mechanism  of,  195 

Hippuric  acid,  368,  381,  742 

Horse's    blood,    peculiar  coagulation  of, 

60 
Howship's  lacunar,  46 
Hunger,  sensation  of,  214 
Hyaline  cartilage,  40 
Hybernation,  state  of  thymus  in,  388 
Hydrobilirubin,  369 
Hydrochloric  acid,  252 
Hydrogen,  732 
Hydrolytic  ferments,  746 
Hymen,  640 
Hyperajsthesia, 

result  of  injury  to  spinal  cord,  484 
Hypermetropia,  601 
Hyperpnoea,  205 
Hyperpyrexia,  499 
Hypoblast,  661 
Hypoglossal  nerve,  545 
Hypoxanthin,  370,  744 


I. 


Ideas,  connection  of,  with  cerebrum,  511 

Ileum,  260 

Ileo-csecal  valve,  266,  268 

Image,  formation  of,  on  retina,  593 

Impulse  of  heart,  123 

Income  of  body,  432  et  seq. 

compared  with  expenditure,  433 
Incus,  569 

function  of,  577 
Indican,  369,  745 
Indigo,  369,  745 
Indol,  272,  745 
Induction 

coil,  408 

current,  408 
Infundibulum,  175 
Inhibitory    influence    of    pneumogastric 

nerve,  131 
Inhibitory  action  of  brain,  511 

on  blood-vessels,  150 
Inhibitory  heat-centre,  323 
Inorganic  matter,  distinction  from  organ- 
ized, 732 

principles,  751 
Inosite,  750 
Insalivation,  239 
Inspiration,  179 

elastic  resistance  overcome  by,  179 

extraordinary,  181 

force  employed  in,  186 

influence  of,  on  circulation,  200 

mechanism  of,  180 
Intercellular  substance,  17 
Intercostal  muscles,  action  in  inspiration, 
180  et  seq. 

in  expiration,  183 
Interlobular  veins,  275 
Internal  capsule,  520 
Intestinal  pice,  289 


Intestines,  digestion  in,  260  et  seq. 

development,  704 

gases,  297 

large,  digestion  in,  292 
structure,  265 

movements,  293 

small,  changes  of  food  in,  290 
structure  of,  260 
Intralobular  veins,  275 
Inversive  ferments,  290 
Involuntary  muscles, 

actions  of,  426 

structure  of,  394 
Iris,  594 

action  of,  594  et  seq. 

in  adaptation  to  distances,  598 

blood-vessels,  591 

development  of,  701 

influence  of  fifth  nerve  on,  595 
of  third  nerve,  595 

relation  of,  to  optic  nerve,  595 
Iron,  753 
Irradiation,  603 


J. 


Jacobson's  nerve,  539 

Jaw,  interarticular  cartilage,  230 

Jejunum,  260 

Juice,  gastric,  250 

pancreatic,  271 
Jumping,  426 


K. 


Karyokinesis,  9 

Katabolic  nerves,  632 

Katacrotic  wave,  141 

Katelectrotonus,  430 

Keratin,  741 

Key,  408 

Kidneys,  their  structure,  353 

blood-vessels  of,  how  distributed,  357 

capillaries  of,  358 

development  of,  706 

function  of,  361.     See  Urine. 

Malpighian  corpuscles  of,  354 

nerves,  359 

tubules  of,  353  et  seq. 
Knee,  pain  of,  in  diseased  hip,  466 
Krause's  membrane,  398 
Kreatin,  380,  743 
Kreatinin,  380,  381,  744 
Kymograph,  144 

tracings,  145 

spring-,  146 


Labia  externa  and  interna,  640 


INDEX. 


771 


Labyrinth  of  the  ear.    See  Ear. 
Lachrymal  apparatus,  585 
gland,  585 

Lactation,  337 
Lacteals,  265 

absorption  by,  309 

contain  lymph  in  fasting,  298 

origin  of,  300 

struct  me  of,  300 

in  villi,  265 
Lactic  acid,  750 

in  gastric  fluid,  252 
Lact  i  terous  ducts,  336 
Lactose,  750 
Lacun;e  of  bone,  46 
Lamellae  of  bone,  48 
Lamina'  dorsales,  664 

viscerales  or  vcntrales,  668 
Large  intestine.     See  Intestine. 
Larynx,  construction  of,  437 

muscles  of,  439 

nerves  of,  440 

variations  in  according  to  sex  and  age, 
445 

ventricles  of,  447 

vocal  cords  of,  438 
Latent  period,  412 
Lateral  plate,  666 
Lateral  ventricles,.  505 
Laughing,  196 

Laxator  tympani  muscle,  569 
Lead  an  accidental  element,  753 
Leaping,  426 
Lecithin,  281,  743 
Legumen  identical  with  casein,  212 
Lens,  crystalline,  591 
Lenticular    ganglion,     relation   of   third 
nerve  to,  531 

nucleus,  521 
Leucic  acid,  742 
Leucin,  272,  742 
Leucocytes.       See      Blood      Corpuscles 

(White) 
Leucocyth;emia,  state  of  vascular  glands 

in,  385 
Levers,  different  kinds  of,  421 
Lieberkiihn's  glands,  262 

in  large  intestines,  269 

in  small  intestines,  263 
Life,  713 

relation  to  other  forces,  718 

simplest  manifestations  of.  3 
Ligamentum  nucha1,  33 
Lightning,  condition  of  blood  after  death 

by,  67 
Lime,  salts  of,  in  human  body,  753 
Lingual  branch  of  fifth  nerve,  537 
Lips,   influence  of  fifth  nerve  on  move- 
ments of,  535 
Liquor  amnii,  671 
Liquor  sanguinis,  or  plasma,  57 

lymph  derived  from,  810 
Liver,  274 

action  of,  on  albuminous  matters,  285 


Liver — continued. 
action  on  saccharine  matters,  287 
blood  elaborating  organ,  286 
blood-vessels  of,  275 

capillaries  of,  275 

cells  of,  275 

circulation  in,  275 

development  of,  705 

ducts  of,  277 

functions  of,  279  et  seq. 

glycogenic  function  of,  286 

secretion  of,  279.     See  Bile. 

structure  of,  276 

sugar  formed  by,  288  et  seq. 
Locus  niger,  500 
Loss  of  water.  752 
Ludwig's  air  pump,  82 
Lungs,  1  73 

blood-supply,  177 

capillaries  of,  177 

cells  of,  175 

changes  of  air  in,  188 

changes  of  blood  in,  193 

circulation  in,  177 

contraction  of,  174 

coverings  of,  173 

development  of,  706 

elasticity  of,  173 

lobes  of,  175 

lobules  of,  1 75 

lymphatics,  177 

muscular  tissue  of,  187 

nerves,  178 

nutrition  of,  177 

position  of,  168 

structure  of,  174 
Luxus  consumption,  217 
Lymph,  308 

compared  with  chyle,  308 
with  blood,  309 

current  of.  303 

quantity  formed,  309 
Lymph-corpuscles,  308 

in  blood,  94 

development  of,  into  red  blood-corpus- 
cles, 93 

origin  of,  92 
Lymph  hearts,   structure   and   action  of, 
304 

relation  of.  to  spinal  cord,  304 
Lymphatic  glands,  305 
Lymphatic  vessels.  298 

absorption  by,  310 

communication  with  serous  cavities,  800 

communication  with  blood-vessels,  800 

course  of  fluid  in.  808 

distribution  of,  29'.) 

origin  of.  299 

propulsion  of  lymph  by,  808 

structure  o\\  808  <  (  an/. 

valves  of,  808 
Lymphoid   or   retiform    tissue,    35.     See 
Adenoid  Tissue. 


772 


INDEX. 


M. 


Macula  germinativa,  636 
Magnesium,  753 
Male  sexual  functions,  652 
Malleus,  569 

function  of,  577 
Malpighian  bodies  or  corpuscles  of  kid- 
ney, 354 

capsules,  354 

corpuscles  of  spleen,  385  et  seq. 
Maltose,  236,  750 
Mammalia, 

blood  corpuscles  of,  72 

brain  of,  509 
Mammary  glands,  335 

evolution,  336 

involution,  337 

lactation,  337 

structure,  335 
Mandibular  arch,  682 
Manganese,  753 
Manometer,  145 

experiments  on  respiratory  power  with, 
184 
Marrow  of  bone,  44 
Mastication,  230 

centre,  496 

fifth  nerve  supplies  muscles  of,  230 

muscles  of,  230 
Mastoid  cells,  568 
Matrix  of  cartilage,  40 
Mature  corpuscles, 

origin  of,  92 
Meatus  of  ear,  568 

venosus,  687 

urinarius,  opening  of,  in  female,  640 
Meckel's  cartilage,  682 
Meconium.  283 
Medulla  of  bone,  44 
Medulla  oblongata,  491  et  seq. 

columns  of,  491 

conduction  of  impressions,  495 

decussation  of  fibres,  492 

effects  of  injury  and  disease  of,  495 

fibres  of,  how  distributed,  492 

functions  of,  495  et  seq. 

important  to  life,  495 

nerve-centres  in,  495 

pyramids  of,  anterior,  491,  492 
posterior,  491,  492 

structure  of,  491 
Medullary  portion  of  kidney.     See  Kid- 
ney. 

folds,  664 

groove,  664 

plate,  664 

substance  of  lymphatic  glands,  306 

substance  of  nerve  fibre,  451 
Meissner's  plexus,  260 
Melanin,  745 
Membrana  decidua,  674 

granulosa,  636 

development  of  into  corpus  luteum, 
649 


Membrana  limitans  externa,  589 
interna,  590 

propria    or  basement  membrane.     See 
Basement  Membrane. 

pupillaris,  701 
capsulo-pupillaris,  701 

tympani;  568 
office  of,  577 
Membrane,  blastodermic,  659 

of  the  brain  and  spinal  cord,  472 

ossification  in,  49 

primary  or  basement      See    Basement 
membrane. 

vitelline,  637 
Membranes  of  brain,  472 
Membranes,   mucous,   328.     See  Mucous. 

membranes. 
Membranes,    passage  of   fluids  through, 
311.     See  Osmosis. 

secreting,  326 
Membranes,    serous,     326.       See    Serous 

membranes. 
Membranous  labyrinth.     See  Ear. 
Memory,  relation  to  cerebral  hemispheres, 

511  et  seq. 
Menstrual    discharge,     composition     of, 

648 
Menstruation,  646 

coincident  with  discharge  of  ova,  647 

corpus  luteum  of,  649 

time  of  appearance  and  cessation,  649 
Mercurial  air-pump,  82 
Mercurial  manometer,  145 
Mercury,  absorption  of,  352 
Mesencephalon,  698 
Mesoblast,  661 
Mesocephalon,  698 
Metallic    substances,    absorption  of,   by 

skin,  352 
Metencephalon,  698 
Methaemoglobin,  86 
Mezzo-soprano  voice,  444 
Micro-organisms,  272 
Micturition,  382 
Milk,  as  food,  211 

chemical  composition,  338 

properties  of,  339 

secretion  of,  337 
Milk-curdling  ferments,  339 
Milk-globules,  338 
Milk-teeth,  221  et  seq. 
Millon's  reagent,  734 
Mind,  cerebral  hemispheres  the  organs  of , 

511 
Mitral  valve,  104 
Modiolus,  572 
Molecules,  or  granules,  4 

in  blood,  70 

in  milk,  338 

movement  of,  in  cells,  4 
Molars.     See  Teeth. 
Molecular  base  of  chyle,  308 
Morphological  development,  12 
Motor  centres,  516 
Motion,  ciliary,  25 


INDEX. 


rs 


Motion — contin  ut  d. 
sensation  of,  576 
Motor  impulses,  transmission  of ,  in  cord. 
483 
nerve-fibres,  457 
laws  of  action  of,  460 
Motor  linguae  nerve.  545 

oculi,  or  third  nerve,  ,"i:;i 
Motor  paths,  483 
Motorial  areas,  516 
Motorial  end-plates,  400 
Mouth,  changes  of  food  in,  220  et  se</. 
Movements, 
of  eyes,  619 
of  intestines,  293 
of  voluntary  muscles,  421 
Mucigen,  233 
Mucin,  740 

Mucous  membrane,  328 
basement  membrane  of,  329 
epithelium-cells  of,    329.     See  Epithe- 
lium, 
digestive  tract,  328 
gastro-pulmonary  tract,  328 
genito-urinary  tract,  329 
gland-cells  of,  329 
of  intestines,  260,  267 
of  stomach,  247 

of  uterus,  changes  of.  in  pregnancy,  674 
respiratory  tract,  328 
Muco-salivary  glands,  233 
Mucus,  329 
Muller's  fibres,  590 
Murexide,  368 
Muscle,  394 
activity,  406 

chemical  constitution,  400 
clot,  402 

contractility,  406 
contraction,  mode  of,  411 
corpuscles,  398 
curves,  412 
development,  401 
disc  of  Hensen,  398 
effect  of  pressure  of,  on  veins,  157 
elasticity,  406 

•electric  currents  in,  404,  418 
fatigue,  415 

curves,  415 
growth,  401 
heart,  399 

heat  developed  in  contraction  of,  416 
involuntary,  394 
actions  of,  426 
Krause's  membrane,  398 
muscle  rods,  399 
natural  currents,  404 
nerves  of,  399 
non-striated,  394 
nutrition  of,  399 
physiology  of,  399 
plain,  394 
plasma,  401 
reaction,  404 
response  to  stimuli,  407,  418 


Muscle — continued. 
rest  of,  403 

ri.uor,  419 

sarcolemma,  396 

sensibility  of,  406 

serum,  401 

shape,  changes  in,  416 

sound,  developed  in  contraction  of,  416 

source  of  action  of,  426 

stimuli,  407 

striated,  396 

structure,  394  et  seq. 

tetanus,  413 

twitch,  411 

unstriped,  394 

voluntary,  396 
actions  of,  421 
blood-vessels  and  nerves  of,  399 

work  of,  415 
Muscular  action,  406 

conditions  of,  418 

force,  415 
Muscular  ''rritability,  406 

duration  of.  after  death,  419 
Muscular  motion,  406  et  so/. 

sense,  527 
cerebellum  the  organ  of,  527 

tone,  490 
Muscularis  mucosa?,  243,  246,  261 
Musculi  papillares,  118 
Musical  sounds,  582 
Myo-albumin.  403 
Myograph,  410 

pendulum,  413 
Myo-haematin,  403 
Myopia,  or  short-sight,  600 
Myosin,  401,  737 

ferment,  402 
Myosinogen,  402 


N. 


Nabothi  glandule,  639 
Nails,  346 

growth  of,  346 

structure  of,  340 
Napthilamine,  872 
Nasal  cavities  in  relation  to    smell,    565 

et  set/. 
Native  albumins,  735 
Natural  organic  compounds,  733 

classification  of.  7:!:: 
Nerve-centre,  465.    .S,  Cerebellum,  Cere- 
brum, lie. 

ano-spinal,  188 

automatic  action,  470 

cardio -inhibitory,  497 

cilio-spinal,  497 

conduction  in,  466 

deglutition,  497 

diabetic,  198 

diffusion  in.  467 

erection,  4*9 

functions  of,  (»;.". 


774 


INDEX. 


Nerve-centre  -  continued. 
genitourinary.  489 
mastication,  230 
micturition,  382 
motor,  516 
radiation  in,  467 
reflexion  in,  467 

laws  and  conditions  of,  467 
respiratory,  197,  497 
secretion  of  saliva,  237 
sweat,  491 

transference  of  impressions,  466 
vaso-motor,  149,  491 
vesico-spinal,  489 
Nerve-corpuscles,  455 
caudate  or  stellate,  455 
polar,  455 
Nerves,  450 
accelerator,  133 
action  of  stimuli  on,  428 

currents  of,  427 
afferent,  458 
axis  cylinder  of,  452 
cells,  455 
centrifugal,  458 
centripetal,  458 
cerebro-spinal,  450 
classification,  457 
conduction  hy,  458  et  seq. 

rate  of,  458 
continuity,  454 
course  of,  454 

cranial.     See  Cerebral  Nerves, 
depressor,  149 
efferent,  458 

electrical  currents  of,  427 
functions  of,  456 

effect  of  chemical  stimuli  on,  428 
of  mechanical  irritation,  428 
of  temperature,  428 
funiculi  of,  453 
gray,  452 
impressions  on,  referred  to  periphery, 

457 
inhibitory,  458.     See  Inhibitory  Action, 
intercentral,  458 
laws  of  conduction,  456  et  seq. 

of  motor  nerves,  460 

of  sensory  nerves,  458 
medullary  sheath,  450 
medullated,  450 
motor,  460 

laws  of  action  in,  460 
natural  currents,  427 
neurilemma,  453 
nodes  of  Ranvier,  452 
non-medullated,  452 
nuclei,  451 
of  special  sense,  460 
plexuses  of,  455 
primitive  nerve  sheath,  450 
sensory,  457 

laws  of  action  in,  458 
size  of,  452 
spinal,  480.     See  Spinal  Nerves. 


Nerves — continued. 
stimuli,  428 
structure,  450 

sympathetic.     See  Sympathetic  Nerve, 
terminations  of,  460 
central,  454 
in  cells,  464 

in  corpuscles  of  Golgi,  463 
in  corpuscles  of  Grandry,  464 
in  corpuscles  of  Herbst,  462 
in  end-bulbs,  463 
in  motorial  end-plates,  398 
in  networks  or  plexuses,  464 
in  Pacinian  corpuscles,  460 
in  touch-corpuscles,  463 
trophic,  633 

ulnar,  effect  of  compression  of,  459 
varieties  of,  450 
vaso-constrictor,  151,  628 
vaso-dilator,  628 
vaso-inhibitory,  628 
vaso-motor,  628 
velocity  of  nerve  force,  458 
white,  451 
Nervi  nervorum,  460 
Nervi  vasorum,  109 
Nervous  force,  velocity  of,  458 
Nervous  S3rstem,  450 
cerebro-spinal,  472 
development,  696 
elementary  structure  of,  450 
influence  of 

on  animal  heat,  323 

on  arteries,  147 

on  contraction  of  blood-vessels,  150 

on  erection,  164 

on  gastric  digestion,  256 

on  the  heart's  action,  128 

on  movements  of  intestines,  294 

of  stomach,  256 
on  respiration,  197 
on  secretion,  323 
on  sphincter  ani,  488 
sympathetic,  625 
Network,  intracellular,  16 

nuclear,  17 
Neural  canal,  664 
Neurenteric  canal,  668 
Neurilemma,  453 
Neurin,  281 
Neuroglia,  36 
Nipple,  an  erectile  organ,  336 

structure  of,  336 
Nitrogen,  732 
in  blood,  89 

influence  of,  in  decomposition,  733 
in  relation  to  food,  210  et  seq. 
in  respiration,  187 
Nitrogenous  compounds,  209 

non-nitrogenous  compounds,  209 
Nitrogenous  equilibrium,  435 
Nitrogenous  food,  210 

in  relation  to  muscular  work,  379  et  seq, 
in  relation  to  urea,  379 
to  uric  acid,  381 


[NDEX. 


Nodes  of  Ranvier,  452 

Non-azotized  or    Non-nitrogenous  fond, 
209 

organic  principles,  747 
Nose.     See  Smell. 

development  of,  703 
Notochord,  664 
Nucleus,  16 

lateralis,  495 

position,  16 

staining  of,  17 
Nutrition   432 

general  nature,  433 
(if  cells.  5 
Nymphae,  640 


O. 


Odontoblasts,  228 
Odors, 

causes  Of,   563  et  Seq. 

different  kinds  of,  566 

perception  of,  563 

varies  in  different  classes,  566 

relation  to  taste,  562 
Oesophagus,  -.'  12 
Oil,  absorption  of,  314 
Oleaginous  principles,  digestion  of,  273 
Oleic  acid,  747 
Olfactory  cells,  565 

centre,  529 

nerve,  563 
subjective  sensations  of,  566 
Olivary  body,  595 

fasciculus,  595 
Omphalomesenteric 

arteries,  692 

duct,  668 

veins,  692 
Oncograpb,  374 
Oncometer,  374 
Ophthalmic  ganglion,    relation  of  third 

nerve,  531 
Ophthalmoscope,  607 
Optic 

lobes,    corpora    quadrigemina     homo- 
logies of.  500 
functions  of,  500 

nerve,  decussation  of,  529 

point  of  entrance  insensible  to  litrlit. 
604 

thalamus,  function  of,  528 

vesicle,  primary,  700 
secondary,  700 
Optical  angle,  611 

apparatus  of  eve,  584 
Ora  serrata  of  retina,  588 
Orang, 

brain  of,  51 1 
Organ  of  Corti,  572 
Organic  compounds  in  body,  ','■>'■', 

instability  of,  788 
Organs  of  sense,  development  of,  700 
Osmosis,  311 


Os  uteri.  639 
Osseous  labyrinth,  570 
Ossicles  Of  the  ear,  569 
Ossicula  audit ns.  569 

Ossification,  49  <t  seq. 
Osteoblasts,  49 

Osteoclasts,  5:', 

Otoconia  or  Otoliths.  574 

use  <>('.  579 
Ovaries,  635 

enlargement  of,  at  puberty,  649 

Graafian  vesicles  in.  636 
<  >visac<.  636 
Ovoblasts,  <;;;n 
Ovum.  686 

action  of  seminal  fluid  on.  657  it  ,v, q, 

changes  of.  in  ovary,  637 

previous  to  formation  of  embryo, 
656 

subsequent  to  cleavage,  658  et  seq 

in  uterus,  658  it  seq. 

cleaving  of  yelk,  658 

connection  of,  with  uterus,  649 

discharge  of,  from  ovary,  649 

formation  of,  637 

germinal  vesicle  and  spot  of,  636  et  seq. 

impregnation,  657 

-tincture  of,  636 

unimpregnated,  636 
Oviduct,  or  Fallopian  tube,  638 
Oxalic  acid,  372 
Oxalic  acid  in  urine,  372 
Oxaluric  acid,  370 
Oxygen,  732 

in  blood,  82 

consumed  in  breathing,  190 

effects  of,  on  color  of  blood,  83 

proportion  of,   to  carbonic  acid,  188  et 
seq. 
Oxyhemoglobin,  85 

spectrum,  85 


P 


Pacchionian  bodies,  472 

Pacinian  bodies  or  corpuscles,  460 

Pain.  550 

Pahnitin,  747 

Pancreas,  270 

development  of.   705 

functions  of,  272  - 1  seq. 

structure,  270 
Pancreatic  fluid,  271 
Papilla  foliata,  588 
Papillae 

of  the  kidney.  353 

of  skin,  distribution  of,  842 

epithelium  of,  348 

of  teeth,  227 

of  tongue,  557 
Paraglobulin,  68,  7'.),  Td&etaeq. 
Parvagum.     Set  Pneumogastric  nerve. 

Paralysis,  cross,  499 

Parapeptone,  258 


776 


INDEX. 


Paraplegia, 

delivery  in,  489 

reflex  movements  in,  489 
Parotid  gland,  saliva  from,  236 

nerves  influencing  secretion  by,  237 
Patellar  reflex,  486 
Paunch,  245 
Pause  in  heart's  action,  121 

respiratorv,  183 
Pecten  of  birds,  701 
Peduncles, 

of  the  cerebellum,  524 

of  the    cerebrum,   or    Crura   Cerebri, 
499 
Pelvis  of  the  kidney,  353 
Penis, 

corpus  cavernosum  of,  163,  643 

development  of,  712 

erection  of,  explained,  163 

structure,  643 
Pepsin,  252 
Pepsinogen,  250 
Peptic  cells,  248 
Peptones,  252,  739  et  seq. 
Pericardium,  97 
Perichondrium,  40 

Perilvmph,  or  fluid  of  labyrinth  of  ear, 
"  570 

use  of,  580 
Perimysium,  396 
Perineurium,  453 
Periosteum,  45 
Peristaltic  movements  of  intestines,  293 

of  stomach,  255 
Perivascular  lymphatic  sheaths,  115 
Permanent  teeth,  222.     See  Teeth. 
Perspiration,  cutaneous,  350 

insensible  and  sensible,  350 

ordinary  constituents  of,  350 
Pettenkofer's  test,  280 
Peyer's  glands,  263 

patches,  263 

structure  of,  263 
Pfliiger's  law,  430 
Phakosocope,  597 
Pharynx,  241 

action  of,  iu  swallowing,  244 

influence  of  glossopharyngeal  nerve  on, 
245 

of  pneumogastric  nerve  on,  245 
Phenol,  272,  751 
Phenomena  of  life,  1 
Phosphates,  753 
Phosphates  in  tissues,  753 
Phosphorus  in  the  human  body,  753 
Pia  mater,  472 
Pigment,  20 
Pigment  cells,  forms  of,  20 

movements  of  granules  in,  20 
Pineal  gland,  392 
Pinna  of  ear,  568 
Pituitary  body,  392 

development,  680 
Placenta,  672  et  seq. 

foetal  and  maternal,  672  et  seq. 


Plants, 

distinctions  from  animals,  10 
Plasma  of  blood,  77 

salts  of,  78 
Plasmine,  62 
composition,  62 
nature  of,  62 
Plethvsmograph,  148 
Pleura,  173 

Pleuro-peritoneal  cavity,  666 
Plexus,  455 

terminal,  400 
Pneumogastric  nerve,  540 
distribution  of,  541 
influence  on 

action  of  heart,  131 
deglutition,  542 
gastric  digestion,  256 
larynx,  542 
lungs,  197 
oesophagus,  542 
pharynx,  542 
respiration,  197 
secretion  of  gastric  fluid,  256 
sensation  of  hunger,  214 
stomach,  256 
mixed  function  of,  542 
origin  from  medulla  oblongata,  540 
Poisoned  wounds,  absorption  from,  314 
Polar  cell,  455 
Pons  Varolii,  its  structure,  499 

functions,  499 
Portal 
blood,  characters  of,  90 
canals,  275 
circulation,  275 

function  of  spleen  with  regard  to,  386 
veins,  arrangement  of,  275  et  seq. 
Portio  dura,  of  seventh  nerve,  538 

mollis,  of  seventh  nerve,  538 
Potassium,  752,  753 

sulphocyanate,  234 
Pregnancy,  absence  of  menstruation  dur- 
ing, 648  et  seq. 
corpus  luteum  of,  652 
influence  on  blood,  89 
Presbyopia,  or  long-sight,  604 
Primitive  groove,  662 

streak,  662 
Primitive    nerve-sheath,     or    Schwann's 

sheath,  511 
Pro-nucleus,  female,  656 

male,  657 
Propionic  acid,  750 
Prosencephalon,  698 
Prostate  gland,  644 
Proteids,  733 
chemical  properties,  734  et  seq. 
physical  properties,  734 
tests  for,  734 
varieties  of,  734 
Proteolytic  ferments,  253 
Protoplasm,  1 
chemical  characters,  3 
movement,  2 


INDEX. 


Protoplasm — continued. 

physical  characters,  3  e t  seq. 

physiological  characters,  3 

reproduction,  7 

transformation  of,  10 
Proto-vertebne,  066 
Psalterium,  246 
Pseudoscope,  624 
Pseudo-stomata,  23 
Ptvalin,  234 

action  of,  235 
Puberty, 

changes  at  period  of,  649 

indicated  by  menstruation,  640 
Pulmonary  artery,  valves  of,  104 

capillaries,  177 

circulation,  177 
Pulse,  arterial  137 

cause  of,  137 

dicrotous,  141 

frequency  of,  126 

influence'of  age  on,  126 
of  food,  posture,  etc.,  126 

relation  of,  to  respiration,  127,  185 

sphygmographic  tracings,  139  et  seq. 

variations,  139  et  seq. 
Purkinje's  figures,  605 
Pylorus,  structure  of,  246 
Pyramidal  portion  of  kidney,  354 
Pyramidal  tracts,  479  et  seq. 
Pyramids  of  medulla  oblongata,  491 

Q. 

Quantity  of  air  breathed,  184 
blood,  57  et  seq. 
saliva,  234 

R. 

Racemose  glands,  330 
Radiation  of  impressions,  467 
Rami  viscerales,  627 

efferentes,  625 

communicautes,  625 
[tectum,  266 

Recurrent  sensibility,  480 
Reflex  actions, 

acquired,  469 

augmentation,  470 

classification,  468 

compound,  469 

conditions  necessary  to,  467 

cutaneous,  485 

in  disease,  468 

examples  of,  485 

excito-motor  and  sensori-motor,  46 

inhibition  of,  486 

irregular  in  disease,  468 

after  separation  of  cord  from  brain, 
512 

laws  of,  469 

morbid,  488 

muscle,  485 


Reflex  actions — contin  »>  d. 

of  medulla  oblongata,  495  et  seq. 
of  spinal  cord,  485 
purposive  in  health,  468 
relation  between  a  stimulus  and,  469 
secondary,  469 
simple.  469 
varieties,  469 
Refracting  media  of  eye,  593 
Refraction,  laws  of,  599 
Regions  of  body.     S<  e  Frontispiece. 
Registering  apparatus, 
cardiograph,  124 
kymograph,  144 
sphygmograph,  138,  139 
Relations  between  secretions,  335 
Remak's  ganglia,  131 
Reptiles, 

blood-corpuscles,  72 
Requisites  of  diet,  218 
Reserve  air.  184 
Residual  air,  184 
Respiration,  167 
abdominal  type,  181 
changes  of  air,  187 

of  blood,  193 
costal  type,  181 
force,  186 
frequency. 185 

influence  of  nervous  system,  203 
mechanism,  180  et  seq. 
movements,  179 
nitrogen  in  relation  thereto,  187 
organic  matter  excreted,  191 
quantity  of  air  changed,  190 
relation  to  the  pulse,  185 
suspension  and  arrest,  204  et  seq. 
types  of,  181 
Respiratory  capacity  of  chest,  184 
cells,  175 

functions  of  skin,  351 
movements,  179 

axes  of  rotation,  179  et  seq. 
of  glottis,  183 

influence  on  amount  of  carbonic  acid, 
188 
on  arterial  tension,  200 
rate,  185 
relation  to  pulse  rate,  185 
size  of  animal,  185 
relation  to  will,  197  et  seq. 
various  mechanism,  193 
muscles,  180  et  &  g. 
daily  work,  186 
power  of,  186 
nerve-centre.  197,  497 
rhythm,  L88 
sounds,  183 
Restiform  bodies,  494  et  eeg. 
iuiiform  or  adenoid,  or  lymphoid  tissue, 

35 
Reticulum,  2  US 
Retina,  588 
blind  spot,  588 
blood-vessels,  591 


778 


INDEX. 


Retina — continued. 
duration  of  impression  on,  605 

of  after-sensations,  606 
excitation  of,  604 
focal  distance  of,  600 
fovea  centralis,  588 
functions  of,  599  et  seq. 
image  on.  how  formed  distinctly,  599 

inversion  of,  how  corrected,  609 
insensible  at  entrance  of  optic  nerve, 

588 
layers,  588 
in  quadrupeds,  590 
reciprocal  action  of  parts  of,  617 
in  relation  to  direction  of  vision,  618 
to  motion  of  bodies,  613 
to  single  vision,  622 
to  size  of  field  of  vision,  611 
structure  of,  588 
vessels,  591 
visual  purple,  608 
Rheoscopic  frog,  42"< 
Rhinencephalon,  698 
Ribs,  axis  of  rotation,  179  et  seq. 
Rigor  mortis,  419 
affects  all  classes  of  muscles,  421 
phenomena  and  causes  of,  420 
Rima  glottidis,  movements  of,  in  respi- 
ration, 183 
Ritter"s  tetanus,  431 
Rods  of  Corti,  572 

use  of,  581 
Rotatory  movements,  500 
Rouleaux,  formation  of,  in  blood,  71 
Ruminants, 

stomach  of,  245 
Rumination,  245 
Running,  mechanism  of,  426 
Rut  or  heat,  646 


S. 


Saccharine  principles  of  food,   digestion 

of,  292 
Saccharoses,  749 
Sacculus,  574 
Saliva,  233 

composition,  234 

process  of  secretion,  241 

quantity,  234 

rate  of  secretion,  234 

uses,  235 
Salivary  glands,  231 

development  of,  705 

influence  of  nervous  system,  233,  497 

mixed,  233 

nerves,  233 

secretion,  233 

structure,  231 

true,  232 

varieties,  232 
Saponification,  27o 
Sarcode,  1.     See  Protoplasm. 


Sarcolemma,  396 

Sarcosin,  744 
Sarcous  elements,  397 
Scala  media,  572 
tympani,  572 
vestibuli,  572 
Scheiner's  experiment,  599 
Schiff's  test,  368 
Schwann's  sheath,  450 
Sclerotic,  585 

Scurvy  from  want  of  vegetables,  213 
Sebaceous  glands,  345 
their  secretion,  349 
Secreting  glands,  329 
aggregated,  330 
convoluted  tubular,  330 
tubular  or  simple,  330 
Secreting  membranes,  326.     See  Mucous 

and  Serous  membranes. 
Secretion,  325 
apparatus  necessary  for,  325  et  seq. 
changes  in  gland-cells  during,  333 
circumstances  influencing,  334 
discharge  of,  333 
influence  of  nervous  system,  334 
of  urine,  377 

process  of  physical  and  chemical,  332 
serous,  326 
synovial,  328 
Segmentation  of  cells,  658 
in  chick,  659 
ovum,  658 
Semen,  652 

composition  of,  652 
emission  of,  a  reflex  act,  489 
filaments  or  spermatozoa,  652 
tubes,  641 
Semicircular  canals  of  ear,  571 
development  of,  702  et  seq. 
use  of,  580 
Semilunar  valves,  104 

functions  of,  118 
Semilunes  of  Heidenhain,  233 
Sensation,  546 
color,  614 
common,  546 

conditions  necessary  to,  546 
excited  by  mind,  546 

by  internal  causes,  546 
of  motion,  549 
nerves  of,  550  et  seq. 
of  pain,  550 
of  pressure,  553 
special,  547 

nerves  of,  550 
stimuli  of,  549 

of  special,  550 
subjective,    548.      See     also      Special 

Senses,  550 
tactile,  550 
temperature,  550 
tickling,  550 
touch,  550 

transference  and  radiation  of,  Wietseq. 
of  weight,  553 


INDEX. 


79 


Senses,  special,  546 

organs  of,  development  of,  700 
Sensory  centres  in  cerebral  cortex,  529 
Sensory  impressions,  conduction  of,  458 
by  spinal  cord,  482 

in  brain,  522 

nerves,  458 

paths,  482 
Septum  between   auricles,    formation  of, 
689 

between  ventricles,  formation  of,  689 

lucid  urn.  689 
Serine,  79,  735 
Serous  fluid,  327 
Serous  membranes,  326 

arrangement  of,  326 

communication    of    lymphatics    with, 
302 

epithelium,  20 

fluid  secreted  by,  327 

functions,  326 

lining  joints,  etc.,  326  it  seq. 
visceral  cavities,  326 

structure  of,  326 
Serum, 

of  blood,  78 

albumin,  735 

separation  of,  78 
Seventh  cerebral  nerve,  538 
Sex,  influence  on  blood,  89 

influence  on    production    of    carbonic 
acid,  188 

relation  of,   to  respiratory  movements, 
181 
Sexual  organs  and  functions  in  the  female, 
634 

in  the  male,  640 
Sighing,  mechanism  of,  195 
Sight,  584.     See  Vision. 
Silica,  parts  in  which  found,  753 
Silicon,  753 

Singing,  mechanism  of,  196  et  acq. 
Single  vision,  condition  of,  620 
Sinus  pocularis,  712 

rhomboidalis.  712 

urogenitals,  712 
Sinuses  of  dura  mater,  162  etscq. 

Of  Valsalva,  104 
Sixth  cerebral  nerve,  537 
Size  of  held  of  vision,  611 
Skatol,  272 

Skeleton.     See  Frontispiece. 
Skin,  340 

absorption  by,  352 
of  metallic  substances,  352 
of  water,  352 

cutis  vera  of,  342 

epidermis  of.  340 

evaporation  from,  350 

excretion  by,  350 

exhalation  of  carbonic  acid  from,  351 
of  watery  vapor  from,  350 

functions  of,  348 
respiratory,  351 

glands,  344 


Skin — continued. 

papilla-  of.  3-42 

perspiration  of,  350 

rete  mucosum  of,  340 

sebaceous  glands  of,  345 

structure  of.  340 

sudoriferous  elands  of,  344 
Sleep,  514 
Smell,  sense  of,  563 

conditions  of,  563 

delicacy,  566 

different  kinds  of  odors,  566 

impaired  by  lesion  of  facial  nerve,  539 

impaired  by  lesion  of  fifth  nerve,  537 

internal  excitants  of.  567 

limited  to  olfactory  region,  563 

structure  of  orpin  of,  564 

subjective  sensations,  566 

varies  in  different  animals,  566 
Sneezing,  centre,  497 

mechanism  of,  195 
Sniffing,  mechanism  of,  196 

smell  aided  by,   563 
Sobbing,  196 
Sodium,  752,  753 

in  human  body,  752,  753 
sulphindigotate,  378 
Solitary  glands.     See  Peyer's. 
Soluble  ferments.  746 
Somatopleure,  666 
Somnambulism,  515 

Sonorous  vibrations,  how  communicated 
in  car,  575  <  t  seq. 

in  air  and  in  water,  ib.     See  Sound. 
Soprano  voice,  444 
Sound, 

binaural  sensations.  5s:: 

conduction  of  by  ear.  575 

heart,  121 

movements  and  sensations  produced  bv, 
584 

perception, 
of  direction  of,  582 
of  distance  of,  583 

permanence  of  sensation  of,  583 

production  of,  582 

subjective.  584 
Source  of  water,  752 
Spasms,  reflex  acts,  498 
Speaking,  447 

mechanism  of,  196,  447 
Special  senses.  54? 
Spectrum-analysis  of  blood,  84 
Speech,  447 

function  of  tongue  in.  549 
Spermatozoa,  development  of,  642 

form  and  structure  of,  652 

function  of,  657 

motion  of,  652 
Spherical  aberration,  602 

correction  of.  602 
Spheroidal  epithelium,  23 
Sphincter  ani.     Set  Defecation. 
Sphygmograph,  188 

tracings,  189  et  seq. 


7S0 


INDEX. 


Spinal  accessory  nerve,  544 
Spinal  cord,  472 

automatism.  471 

canal  of,  473 

centres  in,  488 

a  collection  of  nervous  centres,  488 

columns  of,  474 

commissures  of,  474 

conduction  of  impressions  by,  481  etseq. 

course  of  fibres  in,  479 

decussation  of  sensory  impressions  in, 
483 

development  of,  696 

effect  of  injuries  of,  on  conduction  of 
impressions,  484  et  seq. 

fissures  and  furrows  of,  474 

functions  of,  481 
of  columns,  482 

influence  on  lymph-hearts,  490 
on  sphincter  ani,  488 
on  tone,  490 

morbid  irritability  of,  488 

nerves  of.  477 

reflex  action  of,  485 
in  disease,  488 
inhibition  of,  486 

special  centres  in,  488 

structure  of,  472  et  seq. 

transference,  484 

weight,  510 
relative,  510 

white  matter,  475 
gray  matter,  476 
Spinal  nerves,  477 

origin  of,  479  et  seq. 

physiology  of,  480 
Spirometer,  184j 
Splanchnic  nerves,  149,  627 
Splanchnopleure,  666 
Spleen,  383 

functions,  385 

hilus  of,  383 

influence  of  nervous  system,  386 

Malpighian  corpuscles  of,  385 

pulp,  383  et  seq. 

stroma  of,  383 

structure  of.  383 

trabecular  of,  383  et  seq. 
Splenic  vein,  blood  of,  90 
Spot,  germinal,  636 
Squamous  epithelium,  20 
Stammering,  449 
Stannius'  experiments,  131 
Stapedius  muscle,  569 

function  of,  579 
Stapes,  569 
Starch,  236,  748 

digestion  of 
in  mouth,  235 
Starvation,  215 

appearances  after  death,  216 

effect  on  temperature,  215 

loss  of  weight  in,  215 

period  of  death  in,  216 

symptoms,  216 


Steapsin,  273 
Stearic  acid,  750 
Stearin,  750 
Stercorin,  284 

allied  to  cholesterin,  284 
Stereoscope,  624 
Stimuli,  protoplasmic,  5 
St.  Martin,  Alexis,  case  of,  251 
Stomach,  245 

blood-vessels,  250 

development,  704  et  seq, 

digestion  in,  252 
circumstances  favoring,  253 
products  of,  253 

digestion  after  death,  257 

glands,  248 

lymphatics,  250 

movements,  255 
influence  of  nervous  system,  256 

mucous  membrane,  247 

muscular  coat,  246 

nerves,  256 

ruminant,  245 

secretion  of,  250.     See  Gastric  fluid. 

structure,  246 

temperature,  251 
Stomata,  22,  303 

Stratum  intermedium  (Hannover),  228 
Striated  muscle,  396 
Stroma  fibrin,  61 
Stromuhr,  159 

Structural  basis  of  human  body,  15 
Submaxillary  gland,  238 
Succus  entericus,  289 

functions  of,  290 
Sucking,  mechanism  of,  196 

centre,  497 
Sudoriferous  glands,  344 

their  distribution,  344 

number  of,  344 

their  secretion,  350 
Suffocation,  204  et  seq. 
Sugar.     See  Glucose. 

tests,  236 
Sulphates.  753 

in  tissues,  753 

in  urine,  371 
Sulphuretted  hydrogen,  751 
Suprarenal  capsules,  390 

development  of,  709 

disease  of,  relation  to  discoloration  of 
skin,  392 

structure,  390 
Sun,  a  source  of  energy,  C'nap.  XXIV. 
Swallowing.  244 

centre,  497 

nerves  engaged,  245 
Sweat,  350 
Sympathetic  nervous  system,  465,  625 

conduction  of  impressions  by,  629 

distribution,  465 

divisions  of,  465 

fibres,  differences  of  from  cerebro-spinal 
fibres,  452 

functions,  627  et  seq. 


INDEX. 


>J 


Sympathetic  nervous  system — continued. 
ganglia  of,  629 
action  of,  629  >t  seq. 
co-ordination  of  movements  by,  630 
structure,  62."} 
in  substance  of  organs,  625 
influence  on 

blood-vessels,  147  et  seq. 
heart,  133 

involuntary  motion,  627  et  seq. 
salivary  glands,  238  et  seq. 
secretion,  629 
structure  of,  625 
Synovial  fluid,  secretion  of,  328 

membranes,  328 
Syntonin,  2~>o 
Systemic  circulation.     See  Circulation. 

Vessels,  ib. 
Systole  of  heart,  115 


T. 


Table  of  diet,  219 
Taste..  556 

after- tastes,  562 

centre,  529 

conditions  for  perception  of,  556 

connection  with  smell,  562 

impaired  by  injury 
of  facial  nerve,  539 
of  fifth  nerve,  537 

nerves  of,  540 

seat  of,  556 

subjective  sensations,  563 

varieties,  562 
Taste-goblets,  560 
Taurin,  742 
Taurocholic  acid,  280 
Teeth,  221 

development,  226 

eruption,  times  of,  222 

structure  or,  223  et  «<<?. 

temporary  and  permanent,  221  et  seq. 
Tegmentum,  499 

Temperament,  influence  on  blood,  89 
Tempernture,  316 

average  of  body,  316 

changes  of,  effects  of,  324  et  seq. 

circumstances  modifying,  316 

of  cold-blooded  and  warm-blooded  ani- 
mals, 317 

in  disease,  317 

loss  of,  320 

maintenance  of,  329 

of  Mammalia,  Birds,  etc.,  317 

of  paralyzed  parts,  323 

regulation  of,  319 

of  respired  air,  188 

sensation    of    variation    of,    323.     See 
Heat. 
Temporo-maxillary  fibro-cartilage,  230 
Tendon-reflex,  486 
Tent  Ions,  structure  of,  32 

cells  of,  32 


Tenor  voice,  444 
Tension,  arterial,  143 
Tension  of  gases  in  lungs,  192 
Tensor  tympani  muscle,  579 

office  of,  579 
Tesselated  epithelium,  19 
Testicle,  640 
development,  709 
descent  of,  710 
structure  of,  <">40  <t  stq. 
Tetanus,  413 
Thalamencephalon,  698 
Thalami  optici,  function  of,  523 
Thermogenic   nerves  and   nerve-centres, 

323 
Thirst,  214 
Thoracic  duct.  298 

contents,  309 
Thymus  gland.  387 

function  of,  388 

structure,  387 
Thvro-arytenoid  muscles.  439 
Thyroid  cartilage,  structure  and  connec- 
tions of,  439 
Thyroid- gland.  389 

function  of,  390 

structure,  389 
Timbre  of  voice,  444 
Tissue,  adipose.  37 

areolar,  cellular,  or  connective,  34 

elastic,  33 

fatty.  37 

fibrous,  32 

gelatinous.  35 

ret i form,  35 
Tissues, 

connective,  29 

elementary  structure  of,  30  et  seq. 

erectile,  163 
Tone  of  blood-vessels,  148 

of  muscles,  490 

of  voice,  444 
Tongue,  557 

action  of,  in  deglutition.  244 
in  sucking,  196 

action  of,  in  speech,  449 

epithelium  of.  560 

influence  of  facial  nerve  on,  539 

motor  nerve  of,  545 

an  organ  of  touch,  561 

papillae  of,  558 

parts  most  sensitive  to  taste,  560 

structure  of,  557 
Tonic  centres,  498 
Tonsils.  241 
Tooth-ache,    radiation    of,    sensation    in, 

467 
Touch,  550 

after  sensation.  565 

conditions  tor  perception  of,  550 

connection  of,    with    muscular    sense, 
553 

co  operation  of  mind  with.  555 

hand  an  organ  of,  551 

illusions.  558 


782 


INDEX. 


Touch — continued. 

modifications  of,  550 

a  modification    of  common  sensation, 
550 

special  organs,  550 

subjective  sensations,  556 

the  tongue  an  organ  of,  550 

various  degrees  of,  in  different  parts, 
552 
Touch-corpuscles,  463 
Trachea,  170 

Tracts  in  the  spinal  cord,  479 
Tradescentia  Virginica,     movements    in 

cells  of,  4 
Tragus,  568 

Transference  of  impressions,  466 
Traube-Herihg's  curves,  203 
Tricuspid  valve,  103 

safety-valve  action  of,  118 
Trigeminal  or  fifth  nerve,  533 

effects  of  injury  of,  535 
Trophic  nerves,  536 
Trypsin,  272 
Tripsinogen,  271 
Tubercle  of  Lower,  99 
Tubes,    Fallopian,    638.     See    Fallopian 

tubes. 
Tubular  glands,  330 
Tubules,  18 
Tubuli  seminiferi,  641 

uniferi,  354  et  seq. 
Tunica  albuginea  of  testicle,  640 
Tympanum  or  middle  ear,  568 

development  of,  702 

functions  of,  576 

membrane  of,  577 

structure  of,  577 

use  of  air  in,  576 
Types  of  respiration,  181 
Tyrosin,  272,  743 


U. 


Ulceration  of  parts  attending  injuries  of 

nerves,  631 
Ulnar  nerve, 

effects  of  compression  of,  459 
Umbilical  arteries,  694 

cord,  678 

vesicle,  669 
Unconscious  cerebration,  514 
Unorganized  ferments,  746 
Unstriped  muscular  fibre,  394 

development,  401 

distribution,  394 

structure,  395 
Urachus,  672 
Urate  of  ammonium,  367 

of  sodium,  367 
Urea,  364,  743 

apparatus  for  estimating  quantity,  366 

chemical  composition  of,  364 

identical  with  cyanate  of  ammonium, 
lb.,  365 


Urea — continued. 

properties,  364 

quantity,  366 

in  relation  to  muscular  exertion,  380 

sources,  379 
Ureter,  359 
Uric  acid,  366,  744 

condition  in  which  it  exists  in  urine,  367 

forms  in  which  it  is  deposited,  368 

proportionate  quantity  of,  367 

source  of,  381 

tests,  368 

variations  in  quantity,  368 
Urina  sanguinis,  potus,  et  cibi,  363 
Urinary  bladder,  360    ' 

development,  709 

nerves,  360 

structure,  360 
Urinary  ferments,  362 
Urine,  361 

abnormal,  364 

analysis  of,  361 

chemical  composition,  361 

coloring  matter  of,  368 

cystin  in,  372 

decomposition  by  mucus,  362 

effect  of  blood-pressure  on,  374 

expulsion,  382 

extractives,  370,  381 

flow  of,  into  bladder,  381 

gases,  373 

hippuric  acid  in,  368 

mucus  in,  370 

oxalic  acid  in,  372 

physical  characters,  361 

pigments,  368 

quantity  of  chief  constituents,  362 

reaction  of,  362 
in  different  animals,  362 
made  alkaline  by  diet,  362,  371 

saline  matter,  371 

secretion,  373 

effects  of  posture,  etc.,  on,  382 
rate  of,  382 

solids,  364 
variations  of,  362 

specific  gravity  of,  363 
variations  of,  363 

urates,  367 

urea,  364 

uric  acid  in,  366 

variations  of  specific  gravity,  363 
of  water,  366 
Urobilin,  368 

Urochrome,  368,  745 
Uroerythrin,  369 
Uromelanin,  369 
Uses  of  blood,  94 
Uterus,  639 

change  of  mucous  membrane  of,  673  et 
seq. 

development  of,  in  pregnancy,  673 

follicular  glands  of,  674 

masculinus,  712 

structure,  639 


INDEX. 


7tJ3 


Utriculus  of  labyrinth,  574 
Uvula  in  relation  to  voice,  447 


Vagina,  structure  of,  639 
Vagus  nerve.    8et  Pneumogastric. 
Valve,  ileo-csecal,  structure  of,  200 
Valves  of  heart,  103 

action  of,  117 

bicuspid  or  mitral,  103 

.semilunar,  104 

tricuspid,  103 

of  lymphatic  vessels,  303 

of  veins,  114 
Valvulae  conniventes,  267 
Vas  deferens,  640 
Vasa  efferentia  of  testicle,  041 

ncia  of  testicle,  041 

vasorum,  109 
Vascolar  area,  669 
Vascular  glands,  383 

in  relation  to  blood,  393 

several  offices  of,  393 
Vascular  system,  development  of,  684 
Vaso-constrictor  nerves.  151 
Vasodilator  nerve.-,  151 
Yaso-motor   influence  on  blood  pressure, 

147  etseq. 
Yaso-motor  nerves,  147 

effect  of  section,  148  et  seq. 

influence  upon  blood-pressure,  148 
Yaso-motor  nerve-centres,  149,  498 

reflection  by,  149 
Vegetables  and  animals,  distinctions  be- 
tween, 10 
Veins,  112 

blood-pressure  in,  157 

circulation  in,  156  etseq. 

rate  of,  159 

cardinal,  692 

collateral  circulation  in,  114 

cranium,  162 

development,  692 

distribution,  112 

effects  of  respiration  on,  200 

influence  of  expiration,  202 
inspiration,  200 

influence  of  gravitation  in,  158 

parietal  system  of,  693  et  seq. 

pressure  in,  157 

rhythmical  action  in,  157 

structure  of,  1 13 

systemic,  112 

umbilical,  694 

valves  of,  114 

velocity  of  blood  in,  160 

visceral  system  of.  692  <t  seq. 
Velocity  of  blood  in  arteries,  159 
in  capillaries  160 

in  veins,  160 
of  circulation,  158 
of  nervous  force,  4~>s 
conditions  modifying,  458 
Vena  port  se ,  275 


Venae  hepaticae.  advehentes,  692 
revehentes,  692 

Ventilation,  199 
Ventricles  of  heart .  99 

capacity  of,  116,  127 

contraction  of,  116 

dilatation  of,  ib.,  127 

force  of,  128 

of  larynx,  office  of,  447 

lateral,  505 
Ventriloquism,  449 

Vermicular  movement  of  intestines,  293 
Vermiform  process,  266 
Vertebra?,  development  of,  678 
Vertebral  plate,  666 
Vesicle,  germinal,  636 

Graafian,  636 
Vesicula  germinativa,  636 
Vesiculoe  seminales,  643 

functions  of.  654 

structure,  643 
Vestibule  of  the  ear.  570 
Vibrations,    conveyance    of,  to   auditory 

nerve,  575  et  seq. 
Vidian  nerve,  538 
Villi. in  chorion,  07:1 

in  placenia,  077 
Villi  of  intestines.  264 

action  in  digestion,  265 
Visceral  arches,  development  of,  681 

connection  with  cranial  nerves,  683 

laminae  or  plates.  668 
Visceral  plates,  668 
Viscero-inhibitoiry  nerves,  628 

motor,  628 
Vision,  584 

angle  of,  Oil 

at  different  distances,  adaptation  of  eye 
to,  596  et  seq. 

centre,  529 

corpora   quadrigemina,    the    principal 
nerve-centres  of,  500 

correction  of  aberration,  602  et  seq. 
of  inversion  of  image,  609 

defects  of,  600  et  seq. 

distinctness  of,  how  secured,  598  et  seq. 

duration  of  sensation  in.  605 

estimation  of  the  form  of  objects,  618 
of  their  direction.  613 
of  their  motion,  613 
of  their  size,  612 

field  of,  size  of,  (ill 

focal  distance  of,  599 

impaired  by  lesion  of  fifth  nerve,  587 

influence  of  attention  on,  614 

modified    by    different     parts   of   the 
retina.  617 

purple,  608 

single,  with  two  eyes,  619 
Visual  direction.  618 

Vital  or  respiratory  capacity  of  chest,  184 
Vital  capillary  tone.  156 
Yiteilin.  738  ' 
Vitelline  duct.  704 

membrani 


784 


INDEX. 


Vitelline  spheres,  658 
Vitiated  air,  effects  of,  199 
Vitreous  humor,  594 
Vocal  cords,  438  et  seq. 

action  of,   in  respiratory  actions,   184 
et  seq. 

approximation  of,  effect  on  height  of 
note,  446 

longer  in  males  thau  in  females,  444 

position  of,  how  modified,  442 

vibrations  of,  cause  voice,  438 
Voice,  443 

of  boys,  445 

compass  of,  445 

conditions  on  which  strength  depends, 
446 

human,  produced  by  vibration  of  vocal 
cords,  443 

in  eunuchs,  445 

influence  of  age  on,  445 

of  arches  of  palate  and  uvula,  447 
of  epiglottis,  443 

of  sex,  444 

of  ventricles  of  larynx,  447 

of  vocal  cords,  443 

in  male  and  female,  444 
cause  of  different  pitch,  444 

modulations  of,  444 

natural  and  falsetto,  445 

peculiar  characters  of.  444 

varieties  of,  443  et  seq. 
Vomiting,  258 

action  of  stomach  in,  258 

centre,  497 

nerve-actions  in,  259 

voluntary  and  acquired,  259 
Vowels  and  consonants,  447 
Vulvo-vaginal  or  Duverney's  glands,  640 


W. 


Walking,  423 
Water,  751 
absorbed  by  skin,  352 

by  stomach,  254 
amount, 
in  blood,  variations  in, 


89,  90 


Water— continued. 

exhaled  from  lungs,  190 
from  skin,  350 

forms  large  part  of  human  body,  751 

influence  of  on  decomposition,  733 

in  urine,  excretion  of,  363 
variations  in,  363 

loss  of,  from  body,  752 
uses,  752 

quantity  in  various  tissues,  752 

source,  752 

vapor  of,  in  atmosphere,  190 
Wave  of  blood,  causing  the  pulse,  137 

velocity  of,  137 
White  corpuscles,  94.     See  Blood-corpus- 
cles, white ;  and  Lymph-corpuscles. 
White  fibro-cartilage,  4*2 

fibrous  tissue,  32 
Willis,  circle  of,  162 
Wolffian  bodies,  706  et  seq. 
Wooldridge,  69 
Work  of  heart,  128 


Xanthin.  370,  744 
Xantho-proteic  reaction,  734 


Yawning,  196 
Yelk,  or  vitellus,  637 

changes  of,  in  Fallopian  tube,  658 

cleaving  of,  658 

constriction  of,  by  ventral  laminae,  668 
Yelk-sac,  669  et  seq 
Yellow  elastic  fibre,  33 

fibro-cartilage,  42 

spot  of  Sommering,  588 
Young-Helmholtz  theory,  615 


Z. 


Zimmermann,  corpuscles  of,  388 
Zona  pellucida  658 


QP34 
Ki rkes 


&63 


